DOT HS 811 757 April 2013

The Impact of Hand-Held 

And Hands-Free Cell 

Phone Use on Driving 

Performance and 

Safety-Critical Event Risk

Final Report
DISCLAIMER 

This publication is distributed by the U.S. Department of Transportation, 

National Highway Traffic Safety Administration, in the interest of 

information exchange. The opinions, findings, and conclusions expressed 

in this publication are those of the authors and not necessarily those of the 

Department of Transportation or the National Highway Traffic Safety 

Administration. The United States Government assumes no liability for its 

contents or use thereof. If trade names, manufacturers’ names, or specific 

products are mentioned, it is because they are considered essential to the 

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The United States Government does not endorse products or 

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Suggested APA Format Citation: 

Fitch, G. A., Soccolich, S. A., Guo, F., McClafferty, J., Fang, Y., Olson, R. L., Perez, M. A., 

Hanowski, R. J., Hankey, J. M., & Dingus, T. A. (2013, April). The impact of hand-held 

and hands-free cell phone use on driving performance and safety-critical event risk. 

(Report No. DOT HS 811 757). Washington, DC: National Highway Traffic Safety 

Administration.
i 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

1. AGENCY USE ONLY (Leave blank) 

DOT HS 811 757 

2. REPORT DATE 

April 2013 

3. REPORT TYPE AND DATES COVERED 

Final Report 

4. TITLE AND SUBTITLE 

The Impact of Hand-Held and Hands-Free Cell Phone Use on Driving Performance 

and Safety-Critical Event Risk 

5. FUNDING NUMBERS 

DTNH22-11-D-00236, Task Order 0005 

DTNH22-05-D-1002, Task Order 0022 

6. AUTHOR(S) 

Gregory M. Fitch, Susan A. Soccolich, Feng Guo, Julie McClafferty, Youjia Fang, 

Rebecca L. Olson, Miguel A. Perez, Richard J. Hanowski, Jonathan M. Hankey, and 

Thomas A. Dingus 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

Virginia Tech Transportation Institute 

3500 Transportation Research Plaza (0536) 

Blacksburg, VA 24061

8. PERFORMING ORGANIZATION REPORT 

NUMBER 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

U.S. Department of Transportation 

National Highway Traffic Safety Administration 

1200 New Jersey Avenue SE. 

Washington, DC 20590

10. SPONSORING/MONITORING AGENCY REPORT 

NUMBER 

11. SUPPLEMENTARY NOTES 

Data collection for this study was performed in 2010 by the Virginia Tech Transportation Institute and Westat, Inc., under NHTSA 

contract DTNH22-05-D-1002, Task Order 0022. The Contracting Officer’s Technical Representative for the current study was Lisandra 

Garay-Vega. 

12a. DISTRIBUTION/AVAILABILITY STATEMENT 

This document is available to the public through the National Technical Information 

Service, Springfield, VA 22161. 

12b. DISTRIBUTION CODE 

13. ABSTRACT (Maximum 200 words) 

This study investigated the effects of distraction from the use of three types of cell phones: (1) hand-held (HH), (2) portable handsfree (PHF), and (3) integrated hands-free (IHF). Through a naturalistic driving study (NDS), 204 drivers were continuously 

recorded for an average of 31 days. Only drivers who reported talking on a cell phone while driving at least once per day were 

recruited. A key feature was that drivers provided their cell phone records for analysis, making this the first NDS to date to 

combine call and text records with continuous naturalistic driving data. Results show that drivers talked on a cell phone 10.6 

percent of the time the vehicle was in operation (28% of all calls and 10% of all text messages occurred while the vehicle was 

being operated). Talking on a cell phone, of any type, while driving was not associated with an increased safety-critical event

(SCE) risk. SCEs comprised crashes, near-crashes, and crash-relevant conflicts. Visual-manual (VM) subtasks performed on an 

HH cell phone, however, were associated with an increased SCE risk. HH cell phone use in general was thus found to be associated 

with an increased SCE risk. In contrast, PHF and IHF cell phone use, absent of any VM HH cell phone subtasks, were not found to

be associated with an increased SCE risk. However, VM HH cell phone subtasks were frequently observed during hands-free cell 

phone use. Driver performance when using a cell phone was also investigated through a within-subject comparison. VM HH cell 

phone subtasks were found to significantly increase the percentage of time drivers took their eyes off the forward roadway, while 

talking on an HH cell phone significantly decreased the percentage of time drivers took their eyes off the forward roadway. The

effects of cell phone use on vehicle control were less pronounced. 

14. SUBJECT TERMS 

Cell phone, crash risk, driver distraction, driver performance, integrated hands-free, motor 

vehicle portable electronic device, naturalistic driving, portable hands-free, safety 

15. NUMBER OF PAGES 

273 

16. PRICE CODE 

17. SECURITY CLASSIFICATION OF 

REPORT 

Unclassified 

18. SECURITY CLASSIFICATION OF 

THIS PAGE 

Unclassified 

19. SECURITY 

CLASSIFICATION 

OF ABSTRACT 

20. LIMITATION OF ABSTRACT 
List of Acronyms 

Final Report

ii 

ACRONYMS 

 

ANOVA analysis of variance 

CI confidence interval 

COTR Contracting Officer’s Technical Representative 

DAS data acquisition system 

DF degrees of freedom 

FACS Facial Action Coding System 

FARS Fatality Analysis Reporting System 

F Stat F statistic 

GES General Estimates System 

GPS global positioning system 

HF hands-free 

HH hand-held 

HVAC heat, ventilation, and air-conditioning 

IHF integrated hands-free 

LCL lower confidence limit 

LOS level-of-service 

M mean 

Max maximum 

Min minimum 

n sample size 

NB negative binomial 

NDSs naturalistic driving studies 

NHTSA National Highway Traffic Safety Administration 

NOPUS National Occupant Phone Use Survey 

PHF portable hands-free 

OBD-II on-board diagnostics port 

OR odds ratio 

RV rear vehicle 

SCE safety-critical event 

SHRP2 Strategic Highway Research Program 2 

SE standard error 

SV subject vehicle 
List of Acronyms 

Final Report

iii 

TEORT total eyes off road time 

TTC time-to-collision 

UCL upper confidence limit 

VM visual-manual 
Definitions 

Final Report

iv 

Definitions 

 

Case-control 

approach 

Refers to a method for investigating the safety-critical event risk associated with cell 

phone use and inherent subtasks. Cases (i.e., safety-critical events) are identified. 

Random baseline periods are then selected based on drivers’ exposure. The presence of 

cell phone use and its inherent subtasks in both the cases and baseline periods is then 

determined. The odds of a case occurring when cell phone use is present is then 

compared to the odds of a baseline occurring when just driving takes place. If the 

produced odds ratio and confidence intervals are greater than 1, then it is determined 

that cell phone use is associated with an increased safety-critical event risk relative to 

just driving. 

Cell phone use Refers to when drivers performed visual-manual and/or talking subtasks on a cell 

phone (HH, PHF, or IHF). It does not include holding a cell phone, however. 

Cognitive 

distraction 

Driver distraction is the diversion of attention from activities critical for safe driving to 

a competing activity (US-EU Bilateral ITS Technical Task Force, 2010). Although a 

definition for cognitive distraction is still being developed, it can be thought of as 

occurring when drivers focus their attention away from the driving task. Cognitive 

distraction is difficult to measure in a naturalistic driving study because measurement 

is typically invasive and discourages natural driving behavior. Measures of drivers’ 

physiological state, and self-reports of mental workload immediately after performing 

a cognitive task, were not taken as a result. However, just talking, also referred to as 

“talking/listening” and “conversing” in this report, were investigated. 

Crash 

Any contact with an object, either moving or fixed, at any speed in which kinetic 

energy is measurably transferred or dissipated, and includes other vehicles, roadside 

barriers, objects on or off of the roadway, pedestrians, pedalcyclists, or animals. 

Crash-relevant 

conflict 

Any circumstance requiring a crash avoidance response on the part of the subject 

vehicle, any other vehicle, pedestrian, pedalcyclist, or animal that is less severe than a 

rapid evasive maneuver, but greater in severity than a “normal maneuver” to avoid a 

crash. The crash avoidance response can include braking, steering, accelerating, or any 

combination of control inputs. A crash avoidance response for the SV is defined as a 

control input that falls outside of the 99 percent confidence limit for control input as 

measured for the same subject. 

Curb strike Any crash that results from the subject vehicle making contact (intentional or 

unintentional) with a curb. 

Driving 

Refers to when the vehicle is traveling above 8 km/h. The term ‘vehicle operation’ was 

used to describe when the vehicle ignition was on and the data acquisition system was 

recording. 

General driving Refers to driving in which the driver can perform various non-cell-phone-related 

secondary tasks. An example would be when a driver eats food while driving a vehicle. 
Definitions 

Final Report

v 

Hand-Held 

The term “HH cell phone” was used at the onset of the study when recruiting drivers. It 

described cell phone use where all subtasks (including reaching, dialing, and talking) 

were performed on a hand-held phone. This included holding the cell phone while its 

built-in speakerphone feature was enabled. 

However, for analysis purposes, cell phone interactions were classified as “HH cell 

phone” when the talking/listening subtask was done on a hand-held phone. Cell phone 

interactions that involved the driver using an HH device to place a call, but performing 

the talking/listening subtask on a PHH or IHF cell phone, were not included in this 

category. Note: using the speakerphone feature while the cell phone was not held 

constituted PHF cell phone use. 

Hand-Held: Dialing 

Also reported as “HH: Dial.” Refers to when the driver is pressing buttons or 

interacting with a touch screen on a hand-held cell phone in order to dial a phone 

number to make a call. This can include dialing, searching for a contact’s number, 

entering a voice mail password, etc. It was only specified when the cell records 

indicated that the driver made an outgoing phone call. It did not include pressing a 

button to answer a call (which fell under “HH: locating/reaching/ answering”) or 

pressing a button to end a call (which fell under “HH: End Task”). 

NOTE: Additionally, “HH: Dialing” does NOT include pressing buttons or interacting 

with a touch screen in order to type/read a text message (which should be coded as 

“HH: Text messaging” if driver types or “HH: Viewing/Browsing/Reading” if driver 

reads) or browsing the Internet/using phone applications (which should be coded as 

“HH: Viewing/Browsing/Reading”). 

Hand-Held: End 

task 

Also reported as” HH: End Task.” Refers to when the driver completed a specific cell 

phone interaction by either pressing a button to end the call, putting the phone down 

after ending a call or text, or flipping/sliding the phone closed after ending a call or 

text. 

Hand-Held: Holding 

Also reported as “HH: Hold.” Refers to when the driver held a hand-held cell phone in 

his/her hand but did not interact with it. It did not include when the phone was resting 

on the driver’s seat (next to or between legs), or on the driver’s lap (both of which 

would end the cell phone interaction and be coded as no cell phone task). If the driver 

was viewing, dialing, or performing another subtask with a hand-held phone, and held 

the phone without visually or manually interacting with it for at least 5 consecutive 

seconds, then this “break” period was coded as “HH: Holding.” If the driver resumed 

another (or the same) subtask before the 5-consecutive-seconds period ended, “HH: 

holding” was not coded. Rather, the initial subtask was extended until a new task was 

begun. 

Hand-Held: 

Locate/Reach/ 

Answer 

Also reported as “'HH: Locate/Answer.” Refers to when the driver looks for or reaches 

towards his/her hand-held cell phone. Includes when the driver removes a hand-held 

cell phone from the case before using it. 
Definitions 

Final Report

vi 

Hand-Held: 

Talk/Listen/Voice 

Commands 

Also reported as “HH: Talk/Listen.” Refers to when a driver conversed on a hand-held 

cell phone or had the phone up to his/her ear as if listening to a phone conversation or 

waiting for a person being called to pick up the phone. If the driver used the speaker 

phone function on a hand-held cell phone, then it was coded as “HH: 

Talk/Listen/Voice Commands” if the driver kept the hand-held phone in his/her 

hand(s) while using the speaker phone function. It was coded as “PHF: 

Talk/Listen/Voice Commands” if the driver put the phone down and was no longer 

holding it in his/her hand(s) while using the speaker phone function. 

Hand-Held: Text 

messaging 

Also reported as “HH: Text.” Refers to when a driver is pushing buttons or interacting 

with a touch screen on a hand-held cell phone in order to type a text message. It was 

only specified when the cell records indicated that the driver sent a text message on a 

hand-held phone. It did not include reading a text message, which was coded as “HH: 

Viewing/Browsing/Reading.” If the cell records indicated that the driver received a 

text message, and the driver was seen checking and then replying to this text message 

in the video, then the subtask was coded as follows: 

1. If the driver replied to the text message within 10 seconds after reading the 

text message, then the reply was considered part of the same subtask, and was 

coded as “HH: Text.” The initial reading of the received text message was 

coded as “HH: View/Browse.” 

2. If the driver did not reply to the text message within 10 seconds and simply 

held the phone (coded as “HH: Hold”) for 10+ seconds or put the phone down 

(coded as “HH: End Task”), then the sent text was considered a separate, nonsampled subtask and was not reduced. 

Hand-Held: 

Viewing/Browsing/ 

Reading 

Also reported as “HH: Browse/Read.” Refers to when the driver viewed the hand-held 

cell phone display with or without pressing buttons or manipulating the touch screen 

for a purpose other than making/receiving a call or sending a text message. Examples 

include when the driver used the cell phone to check the time, read a received text 

message, browse the Internet or email, or use the phone’s other applications. This 

included reading a received text message. Exceptions included: 

1) When a call was ending, the subtask was coded as “HH: End Task” if the 

driver looked at the phone and/or pressed a button to end a call. 

2) When a call was being answered, any glances or associated button presses 

were coded as “HH: Locate/Reach/Answer.” 

Hands-Free (HF) A general term used to describe portable hands-free and integrated hands-free cell 

phones. 

Headway 

Also known as following distance, this is a measurement of the time between two 

vehicles in a transit system. It is computed by dividing the range to the lead vehicle by 

the travel speed of the subject vehicle (SV). The unit of measurement is seconds, and 

reflects the amount of time that it would take for the SV to reach the position of the 

lead vehicle at that instant in time. 
Definitions 

Final Report

vii 

Integrated Hands--

Free (IHF) 

The term “IHF cell phone” was used at the onset of the study when recruiting drivers. 

It described cell phone use where some cell phone subtasks, including reaching, 

dialing, and talking, were done with a cell phone technology that was integrated into 

the vehicle. This included equipment installed by the vehicle manufacturer such as 

microphones and speakers for cell phone use, a speech-based user interface to dial the 

phone, and other phone controls built into the vehicle (e.g., center stack and/or steering 

wheel buttons). IHF included both vehicles that had a cell phone built into the vehicle 

itself, and vehicles that detected and interacted with the user’s portable device without 

requiring direct manipulation of the phone itself. 

However, for analysis purposes, cell phone interactions were classified as “IHF cell 

phone” when the talking/listening subtask involved the use of cell phone technology 

that was integrated into the vehicle. This included equipment installed by the vehicle 

manufacturer such as microphones and speakers for cell phone use, a speech-based 

user interface to dial the phone, and other phone controls built into the vehicle (e.g., 

center stack and/or steering wheel buttons). Integrated Hands-free devices included 

vehicles that had a cell phone built into the vehicle itself, and vehicles that detected 

and interacted with the user’s nomadic device requiring direct manipulation of the 

phone itself. Cell phone interactions involving the driver using an IHF device to place 

a call, but then talking/listening on an HH or PHF cell phone, were not included in this 

category. 

Integrated Handsfree: Press button to 

begin/answer 

Also reported as “IHF: Begin/Answer.” Refers to when the driver pressed a button on 

the steering wheel or center stack in order to begin a cell phone interaction. It included 

pushing to answer a call, pushing to voice dial, or pushing to enter a voice command. 

Integrated HandsFree: Press button 

to end 

Also reported as “IHF: End Task.” Refers to when the driver pressed the button on the 

steering wheel or center stack in order to end the cell phone interaction. 

Integrated HandsFree: 

Talk/Listen/Voice 

commands 

Also reported as “IHF: Talk/Listen.” Refers to when a driver talked, listened, or gave 

voice commands on an integrated device. The driver had to be observed talking 

repeatedly with no obvious passenger interaction. Additionally, this subtask was only 

coded when the cell records indicated that the driver made or received a call. 

Intersection 

violation 

Any stop at a controlled intersection where the subject vehicle either (1) stops past the 

stop bar and/or in the path of cross traffic, (2) performs a rolling stop at a stop sign or 

right-on-red with a minimum speed >=15mph regardless of relation to stop bar, or (3) 

passes through a red light in a straight crossing or left turn path. 

Just driving Refers to driving in which the driver does not perform any observable non-drivingrelated secondary tasks. It is considered the purest form of driving. 

Just talking Refers to when a driver is conversing on a cell phone and not performing any other cell 

phone subtasks; in particular, visual-manual cell phone subtasks. 
Definitions 

Final Report

viii 

Near-crash 

Any circumstance requiring a rapid, evasive maneuver by the subject vehicle (SV), or 

any other vehicle, pedestrian, pedalcyclist, or animal to avoid a crash. A rapid, evasive 

maneuver is defined as a steering, braking, accelerating, or any combination of control 

inputs that approaches the limits of the vehicle capabilities. As a guide: SV braking 

>0.5 g or steering input that results in a lateral acceleration >0.4 g to avoid a crash 

constitutes a rapid maneuver. 

Portable Hands-free 

(PHF) 

The term “PHF cell phone” was used at the onset of the study when recruiting drivers. 

It described cell phone use during which some cell phone subtasks, including reaching, 

dialing, and talking were performed with a PHF device. PHF devices included headsets 

(wired or wireless) or other aftermarket Bluetooth or hands-free devices that were not 

integrated into the vehicle by the manufacturer. PHF included voice activation 

performed through the PHF device. 

However, for analysis purposes, cell phone interactions were classified as “PHF cell 

phone” when the talking/listening subtask was done on a portable hands-free device. 

Portable Hands-Free devices included headsets (wired or wireless) or other aftermarket 

Bluetooth or hands-free devices that were NOT integrated into the vehicle by the 

manufacturer. PHF could include some voice activation. Cell phone interactions 

involving the driver using a PHF device to place a call, but then talking/listening on an 

HH or IHF cell phone, were not included in this category. 

Portable Hands--

Free: 

Holding/Wearing 

Headset/Earpiece 

Also reported as “PHF: Hold/Wear.” Refers to when a driver was holding a 

headset/earpiece in his/her hand or wearing it on his/her head but not interacting with it 

(and not involved in a phone conversation). 

Portable Hands--

Free: Locate/Put-on 

Headset/Earpiece 

Also reported as “PHF: Locate/Put on.” Refers to when the driver looked for or 

reached towards a headset or earpiece. 

Portable Hands--

Free: Push button to 

begin/answer 

Also reported as “PHF: Begin/Answer.” Refers to when the driver pressed a button on 

the headset/earpiece in order to begin a cell phone interaction. This included pushing to 

answer a call or pushing to give a voice command to make a call. This button may be 

located on the headset/earpiece itself, or occasionally somewhere on the wire 

connecting the device to the phone. Note, if the driver pushed a button or dialed on a 

hand-held phone instead of pushing a button on the headset/earpiece to answer or make 

a call, then this was coded as “HH: Dialing” or “HH: Locate/Reach/Answer,” even if 

the subsequent conversation took place via a Portable Hands Free device. 

Portable Hands--

Free: Push button to 

end 

Also reported as “PHF: End Task.” Refers to when the driver pressed the button on the 

headset/ear piece in order to end the cell phone interaction. The button could be 

located on the headset/earpiece itself, or occasionally somewhere on the wire 

connecting the device to the phone. If the driver pushed a button on a hand-held phone 

instead of pushing a button on the headset/earpiece to end a call, then this subtask was 

coded as “HH: End Task,” even if the conversation took place via a portable handsfree device. 
Definitions 

Also reported as “PHF: Talk/Listen.” Refers to when a driver talked on a headset, 

earpiece, or other aftermarket device, OR listened to a phone conversation, OR waited 

for a person being called to pick up the phone. The driver had to be observed talking 

repeatedly with no obvious passenger interaction to conclude that the headset/earpiece Portable Hands-- was in use. This subtask was coded if the talking subtask was performed on a portable 

Free: hands-free device, even if the dialing, answering, or call-ending subtask was performed 

Talk/Listen/Voice using a hand-held phone. If the driver used the speaker phone function on a hand-held 

commands cell phone, then the subtask was coded as “hand-held: Talk/Listen/Voice Commands” 

if the driver kept the hand-held phone in his/her hand(s) while using the speaker phone 

function. It was coded as “Portable Hands-Free: Talk/Listen/Voice Commands” if the 

driver put the phone down and was, thus, not holding it in his/her hand(s) while using 

the speaker phone function. 

Refers to a method for investigating the safety-critical event risk associated with cell 

phone use and inherent subtasks. It is a ratio of two rates. The first rate is the number 

of safety-critical events that occur when using a cell phone divided by the number of 

minutes spent using a cell phone while driving. The second rate is the number of 

Risk rate approach safety-critical events that occur when not using a cell phone divided by the number of 

minutes spent not using a cell phone while driving. If the first rate is found to be 

greater than the second rate using a mixed-effect Poisson regression, then using a cell 

phone is determined to be associated with an increased safety-critical event risk. The 

method is used to investigate risk relative to general driving. 

Refers to unsafe driving. A safety-critical event can be a crash (where measurable 

contact is made between the subject vehicle and an object), a near-crash (where a crash 

Safety-critical event would have transpired had a rapid evasive maneuver not been made), and a crashrelevant conflict (which is a conflict that is less severe than a near-crash, but more 

severe than normal driving). 

When considering a specific driving time interval, Total Eyes Off Road Time 

Total eyes off road (TEORT) refers to the sum of all glances away from the forward roadway (including 

time glances to the side and rear-view mirrors) that are made during the time interval. It is a 

measure of visual distraction. 

Vehicle Refers to when the vehicle ignition is on and the data acquisition system is recording. operation 

Final Report

ix 

Table of Contents 

TABLE OF CONTENTS 

Acronyms ....................................................................................................................................... ii 

Definitions ..................................................................................................................................... iv 

Executive Summary ................................................................................................................. xxiii

Objective 1: Investigate Drivers’ Cell Phone Use ...................................................... xxiii

Objective 2: Investigate SCE Risk Associated With Cell Phone Use ........................ xxiv

Objective 3: Investigate Driver Performance When Using a Cell Phone ................... xxvi

Summary .................................................................................................................. xxvii

1 Introduction ............................................................................................................................1

1.1 Study Rationale .......................................................................................................1

2 Background ............................................................................................................................3

2.1 Driver Distraction From Cell Phone Use ................................................................3

2.1.1 Drivers’ Cell Phone Use ...................................................................................... 3

2.1.2 Crash Risk of Using a Cell Phone ........................................................................ 4

2.1.3 Driver Performance When Using a Cell Phone ................................................... 5

2.2 Designing to Mitigate Distraction From Cell Phones .............................................7

3 Methods ...................................................................................................................................9

3.1 Driver Demographics ..............................................................................................9

3.2 Data Collection ......................................................................................................11

3.3 Data Reduction ......................................................................................................13

3.3.1 Cell Phone Records ............................................................................................ 13

3.3.2 Driver Verification ............................................................................................. 14

3.3.3 Trip Summary ..................................................................................................... 14

3.3.4 Cell Phone Use While Driving ........................................................................... 14

3.3.5 Cell Phone Use Baseline Periods ...................................................................... 16

3.3.6 SCE Identification .............................................................................................. 16

4 Investigation of Drivers’ Cell Phone Use ...........................................................................19

4.1 Calls Analyzed According to the Cell Phone Records ..........................................19

4.2 Calls Analyzed According to the Cell Phone Reduction ......................................21

4.2.1 Distribution of Calls across Groups Assigned During Recruitment .................. 21

4.2.2 Call and Text Rate by Cell Phone Type ............................................................. 22

4.2.3 Duration of Cell Phone Use by Cell Phone Type ............................................... 22

4.2.4 Frequency and Duration of Cell Phone Subtasks .............................................. 23

4.2.5 Frequency of Non-Cell-Phone Secondary Tasks ............................................... 28

4.2.6 Comparison of Actual Call Duration to Cell Phone Records ............................ 29

4.2.7 Percentage of Subtasks With Both Hands Removed From Steering Wheel ....... 29

4.2.8 Emotional Demeanor During Calls ................................................................... 30

4.2.9 Where Phone is Held During Subtask ................................................................ 30

4.2.10 Type of Cell Phone Used .................................................................................... 31

4.2.11 Where Phone was Kept Prior to Reaching......................................................... 32

4.2.12 Cell Phone Use in Low and High Driving Task Demands ................................. 32

Final Report

xi 
Table of Contents 

5 Investigation of the Risk of an SCE Associated With Cell Phone Use ............................33

5.1 Risk Rate Approach ..............................................................................................33

5.1.1 SCE Rate ............................................................................................................ 33

5.1.2 Data Processing ................................................................................................. 34

5.1.3 Estimation Procedure......................................................................................... 34

5.1.4 Analysis .............................................................................................................. 36

5.1.5 Results ................................................................................................................ 37

5.2 Case-Control Approach .........................................................................................39

5.2.1 Equations ........................................................................................................... 39

5.2.2 Results ................................................................................................................ 40

6 Investigation of Driver Performance When Using a Cell Phone .....................................41

6.1 Performance Degradation when Using a Cell Phone ............................................44

6.1.1 Percent Total-Eyes-Off-Road Time .................................................................... 44

6.1.2 TEORT Duration ................................................................................................ 48

6.1.3 Speed Standard Deviation .................................................................................. 49

6.1.4 Headway Standard Deviation ............................................................................ 49

6.1.5 Unintentional Lane Bust Rate ............................................................................ 50

6.1.6 Delayed Reaction to Unexpected External Event .............................................. 50

6.1.7 Peak Deceleration .............................................................................................. 51

6.1.8 Driver Performance When Using a Cell Phone Near Intersections .................. 51

6.1.9 Drivers’ Turn Signal Use When Changing Lanes .............................................. 52

6.2 Driver Adaptation When Using a Cell Phone .......................................................52

6.2.1 Speed .................................................................................................................. 52

6.2.2 Headway ............................................................................................................. 53

6.2.3 TTC..................................................................................................................... 53

6.2.4 SV Lane Change Behavior ................................................................................. 53

6.2.5 SV Lane Position ................................................................................................ 54

6.3 Downstream Effects From Drivers Using a Cell Phone .......................................55

6.3.1 Range to Rear Vehicle ........................................................................................ 55

6.3.2 Rear Vehicle Lane Change Behavior ................................................................. 56

7 Discussion ..............................................................................................................................57

7.1 Drivers’ Cell Phone Use ........................................................................................57

7.2 SCE Risk Associated With Cell Phone Use ..........................................................59

7.3 Driver Performance While Using a Cell Phone ....................................................60

7.4 Summary ...............................................................................................................62

8 Limitations ............................................................................................................................63

9 Acknowledgements ..............................................................................................................65

10 References .............................................................................................................................67

APPENDICES ..............................................................................................................................71

A.1 Data Elements and Dependent Measures ..............................................................72

A.2 Cell Phone Provider Billing Policies .....................................................................73

A.3 Operational Definitions for Cell Phone Subtasks .................................................74

Final Report

xii 
Table of Contents 

A.4 Driver, Vehicle, and Environmental Factors Coded for Cell Phone Subtasks ......86

A.5 Definition of Eyeglance Locations ......................................................................106

A.6 Subtask-Level Kinematic Data ...........................................................................109

A.7 Driver, Vehicle, and Environmental Questions for Safety-Critical Events ........112

A.8 Characterization of Safety-Critical Events ..........................................................135

A.9 Driver, Vehicle, and Environmental Questions for Safety-Critical Event Baseline 

Periods .................................................................................................................156

A.10 Investigation of Drivers’ Cell Phone Use ...........................................................179

A.10.1 Duration of Calls and Text Messages by Cell Phone Type ................................ 179

A.10.2 Frequency and Duration Talk/Listen Subtask .................................................... 182

A.10.3 Frequency and Duration of Subtasks .................................................................. 183

A.10.4 Frequency of Non-Cell Secondary Tasks ............................................................ 187

A.10.5 Percentage of Subtasks With Both Hands Removed From Steering Wheel ........ 189

A.10.6 Where Phone Was Held During Subtask ............................................................ 193

A.10.7 Where Phone Was Kept Prior to Reaching ........................................................ 193

A.10.8 Low and High Task Demand Analyses ............................................................... 194

A.11 Risk Rate Approach Estimation Details ..............................................................196

A.11.1 Estimating Overall Talk/Listen Time ............................................................... 196

A.11.2 Estimating Talk/Listen Time for the Three Cell Phone Types.......................... 197

A.11.3 Estimating Visual-Manual Subtask Time During Calls ................................... 198

A.11.4 Estimating Visual-Manual Subtask Time During Text Messages .................... 198

A.11.5 Estimating Overall Visual-Manual Time ......................................................... 199

A.11.6 Estimating the Visual-Manual Time for the Three Cell Phone Types .............. 200

A.11.7 Estimating the Total Cell Phone Use Time ...................................................... 201

A.11.8 Estimating the Total Cell Phone Use Time for the Three Cell Phone Types ... 201

A.11.9 Estimating the Total General Driving Time ..................................................... 202

A.12 Driver Performance ANOVA Results .................................................................203

A.12.1 Percent TEORT ................................................................................................ 203

A.12.2 TEORT Duration .............................................................................................. 203

A.12.3 Speed Standard Deviation ................................................................................ 205

A.12.4 Headway Standard Deviation .......................................................................... 207

A.12.5 Unintentional Lane Bust Rate .......................................................................... 210

A.12.6 Peak Deceleration ............................................................................................ 213

A.12.7 Driver Performance When Using a Cell Phone Near Intersections ................ 217

A.13 Driver Adaptation ANOVA Results ...................................................................218

A.13.1 Speed ................................................................................................................ 218

A.13.2 Headway ........................................................................................................... 221

A.13.3 TTC................................................................................................................... 224

A.13.4 SV Lane Change Behavior ............................................................................... 227

A.13.5 SV Lane Position .............................................................................................. 231

A.14 Downstream Effects from Drivers Using a Cell Phone ANOVA Results .....235

A.14.1 Range to Rear Vehicle ...................................................................................... 235

A.14.2 Rear Vehicle Lane Change Behavior ............................................................... 238

Final Report

xiii 
Table of Contents 

A.15 Exploratory Analyses ..........................................................................................241

A.15.1 SCE Risk Associated With Emotional Conversation ........................................ 241

A.15.2 Likelihood of Scanning Intersection When Using a Cell Phone While 

Stopped ....................................................................................................................... 241

A.15.3 Drivers’ Mean Trip Time by Location ............................................................. 242

Final Report

xiv 
List of Tables 

LIST OF TABLES 

Table 1. SCE Risk Associated With Cell Phone Use as Computed Through 

Risk Rate Approach .......................................................................................................... xxv

Table 2. SCE Risk Associated With Cell Phone Use as Computed Through 

Case-Control Approach ..................................................................................................... xxv

Table 3. Definition of Cell Phone Type Used in Recruiting Drivers ............................................... 9

Table 4. Distribution of Participants by Cell Phone Usage Group and Location ........................... 9

Table 5. Summary of State Cell Phone Laws ............................................................................ 10

Table 6. Cell Phone Provider Billing Policies .............................................................................. 14

Table 7. Subtasks Reduced ........................................................................................................ 15

Table 8. Algorithm Logic Used to Trigger Potential SCEs .......................................................... 16

Table 9. Percentage of SCE Triggers That Were Valid .............................................................. 17

Table 10. SCE Severity Classification ........................................................................................ 17

Table 11. Frequency and Percentage of Sampled Cell Phone Interactions by 

Cell Phone Type .................................................................................................................. 19

Table 12. Frequency and Percentage of Call Interactions by Cell Phone Type 

Across Groups Assigned During Recruitment ..................................................................... 22

Table 13. Phone Interaction Descriptive Statistics With Kruskal-Wallis Test Results 

 for Duration – Above 8 km/h .............................................................................................. 23

Table 14. Phone Interaction Descriptive Statistics With Kruskal-Wallis Test Results 

for Duration – Below 8 km/h ................................................................................................ 23

Table 15. Cell Phone Subtask Frequency and Duration With Summary Statistics ..................... 24

Table 16. Talk/Listen Subtask Descriptive Statistics With Tukey Test Results for 

Duration – Above 8 km/h ..................................................................................................... 27

Table 17. Talk/Listen Subtask Descriptive Statistics With Tukey Test Results for 

Duration – Below 8 km/h ..................................................................................................... 27

Table 18. Percentage of Subtasks With Both Hands Removed From Steering Wheel by 

Cell Phone Type .................................................................................................................. 30

Table 19. Where Phone Was Held During Subtask by Driver Location and Speed ................... 31

Table 20. Type of Phone Used During Hand-Held Subtask ....................................................... 31

Table 21. Significant Results of Chi-Square Tests on the Duration of Cell Phone Subtasks 

Across Driving Task Demands ............................................................................................ 32

Table 22. Risk Rate Ratios for Cell Phone Use Subtasks and Aggregate Use While Driving .... 38

Table 23. 2x2 Contingency Table for Cell Phone Use and SCE Outcome ................................. 39

Table 24. Contingency Table for Talking on a Cell Phone and SCE Outcome ........................... 39

Table 25. Odds Ratios for Cell Phone Use Subtasks and Aggregate Use While Driving ........... 40

Table 26. Driver Performance Degradation Measures ............................................................... 41

Table 27. Driver Adaptation Measures ....................................................................................... 43

Table 28. Measures of Effects on Downstream Traffic ............................................................... 43

Table 29. ANOVA Results for Within-Subject Comparisons of Mean Percent TEORT 

Between Each Subtask and Its Matched Baseline .............................................................. 45

Final Report

xv 
List of Tables 

Table 30. Mean Percent TEORT Difference Scores for Various Subtasks Across Cell Phone 

Types .................................................................................................................................. 47

Table 31. Mean TEORT Durations Collapsed Across Cell Phone Types ................................... 48

Table 32. Frequency of Driver Delayed Reaction to Unexpected External Event ....................... 50

Table 33. Frequency of Driver Delayed Reaction to Unexpected External Event by Subtask .... 51

Table 34. Results for Between-Subjects Comparisons of SV Lane Change Behavior When 

Ending Cell Phone Use Across Cell Phone Types .............................................................. 54

Table 35. Estimates of Drivers’ Cell Phone Use ......................................................................... 58

Table 36. Data Elements and Dependent Measures .................................................................. 72

Table 37. Definitions of Eyeglance Locations From Reduction Protocol .................................. 106

Table 38. Descriptive Kinematic Measures ............................................................................... 109

Table 39. Driving Performance Degradation Measures ............................................................ 110

Table 40. Driver Adaptation Measures ..................................................................................... 111

Table 41. Results of Kruskal-Wallis Tests on Duration Between Phone Types ........................ 179

Table 42. Descriptive Statistics for Cell Phone Subtask Durations ........................................... 180

Table 43. Frequency and Average Duration of Talk/Listen Subtask Across Cell Phone 

Types by Speed Level ....................................................................................................... 182

Table 44. Results of ANOVA for Log Duration of Talk/Listen Subtask for Driving Speed 

Above 8 km/h .................................................................................................................... 182

Table 45. Results of ANOVA for Log Duration of Locate/Answer or Locate/Put on 

Subtask for Driving Speed Below 8 km/h .......................................................................... 182

Table 46. Confidence Intervals (95%) for Difference Between Log Means of Duration of 

Talk/Listen Subtask Across Cell Phone Types by Speed Level ........................................ 182

Table 47. Frequency and Average Duration of Locate/Answer or Locate/Put on 

Subtask Across Cell Phone Types by Speed Level .......................................................... 183

Table 48. Results of ANOVA for Log Duration of Locate/Answer or Locate/Put on 

Subtask for Driving Speed Above 8 km/h ......................................................................... 183

Table 49. Results of ANOVA for Log Duration of Locate/Answer or Locate/Put on 

Subtask for Driving Speed Below 8 km/h .......................................................................... 183

Table 50. Confidence Intervals (95%) for Difference Between Log Means for 

Locate/Answer or Locate/Put on Subtask Across Cell Phone Types by Speed Level ...... 184

Table 51. Frequency and Average Duration of Hand-Held Dialing or Portable HandsFree/Integrated Hands-Free Begin/Answer Subtask Across Cell Phone Types by 

Speed Level ...................................................................................................................... 184

Table 52. Results of ANOVA for Log Duration of Hand-Held Dialing or Portable HandsFree/Integrated Hands-Free Begin/Answer Subtask for Driving Speed Above 8 km/h ..... 184

Table 53. Results of ANOVA for Log Duration of Hand-Held Dialing or Portable HandsFree/Integrated Hands-Free Begin/Answer Subtask for Driving Speed Below 8 km/h ..... 185

Table 54. Confidence Intervals (95%) for Difference Between Log Means of Duration of 

Hand-Held Dialing or Portable Hands-Free/Integrated Hands-Free Begin/Answer 

Subtask Across Cell Phone Types by Speed Level .......................................................... 185

Table 55. Frequency and Average Duration of Browse/Read While Talking/Listening 

Subtask Across Cell Phone Types by Speed Level .......................................................... 185

Table 56. Results of ANOVA for Duration of Browse/Read While Talking/Listening 

Subtask for Driving Speed Above 8 km/h ......................................................................... 185

Final Report

xvi 
List of Tables 

Table 57. Results of ANOVA for Duration of Browse/Read While Talking/Listening 

Subtask for Driving Speed Below 8 km/h .......................................................................... 186

Table 58. Confidence Intervals (95%) for Difference Between Log Means of Duration 

of Browse/Read While Talking/Listening Subtask Across Cell Phone Types by 

Speed Level ...................................................................................................................... 186

Table 59. Frequency and Average Duration of End Task Subtask Across Cell Phone 

Types by Speed Level ....................................................................................................... 186

Table 60. Results of ANOVA for Log Duration of End Task Subtask for Driving Speed 

Above 8 km/h .................................................................................................................... 187

Table 61. Results of ANOVA for Log Duration of End Task Subtask for Driving Speed 

Below 8 km/h ..................................................................................................................... 187

Table 62. Confidence Intervals (95%) for Difference Between Log Means of End Task 

Subtask Across Cell Phone Types by Speed Level .......................................................... 187

Table 63. Frequency Counts for Secondary Task “Adjusting Radio/HVAC Observed” ............ 188

Table 64. Frequency Counts for Secondary Task “Eating/Drinking” ......................................... 188

Table 65. Frequency Counts for Secondary Task “Reading/Writing”........................................ 188

Table 66. Frequency Counts for Secondary Task “Adjusting/Monitoring Other Devices 

Integral to Vehicle” ............................................................................................................ 188

Table 67. Fisher’s Exact Test Results for Percentage of Subtasks With Both Hands 

Removed From Steering Wheel Across Cell Phone Types by Speed Level ..................... 189

Table 68. Count and Percentage of Observations With Both Hands Removed From 

Steering Wheel Across Cell Phone Subtasks by Speed Level ......................................... 190

Table 69. Fisher’s Exact Test Results for Percentage of Browse/Read During 

Talking/Listening Subtask With Both Hands Removed From Steering Wheel 

Across Cell Phone Types by Speed Level ........................................................................ 192

Table 70. Reduction Categories for Phone Location During Use and Corresponding 

Visibility Classification ....................................................................................................... 193

Table 71. Cell Phone Subtask Duration in Low and High Task Demands With 

Significance Test Results .................................................................................................. 195

Table 72. Average Time Lost per Call in the Cell Phone Records Stratified by 

Call Direction and Cell Phone Type Group Drivers Were Originally Assigned .................. 196

Table 73. Proportion of Talk Time Spent on an HH, PHF, or IHF Cell Phone 

During Incoming Calls in the Cell Phone Records ............................................................ 197

Table 74. Proportion of Talk Time Spent on an HH, PHF, or IHF Cell Phone 

During Outgoing Calls in the Cell Phone Records ............................................................ 197

Table 75. Proportion of Talk Time Spent on an HH, PHF, or IHF Cell Phone 

During Calls of Unknown Direction in the Cell Phone Records ......................................... 197

Table 76. Average Amount of Time Spent Performing Visual-Manual Subtasks per Call ........ 198

Table 77. Average Amount of Time Spent Performing Visual-Manual Subtasks per Text........ 198

Table 78. Average Text Messaging Duration by Cell Phone Group ......................................... 199

Table 79. Proportion of Visual-Manual Time Spent on an HH, PHF, or IHF 

Cell Phone During Incoming Calls .................................................................................... 200

Table 80. Proportion of Visual-Manual Time Spent on an HH, PHF, or IHF 

Cell Phone During Outgoing Calls .................................................................................... 200

Final Report

xvii 
List of Tables 

Table 81. Proportion of Visual-Manual Time Spent on an HH, PHF, or IHF 

Cell Phone During Calls of Unknown Direction ................................................................. 200

Table 82. ANOVA Results for Between-Subject Comparisons of TEORT Durations for 

Subtasks that Perform a Similar Function ......................................................................... 204

Table 83. ANOVA Results for Within-Subject Comparisons of Speed Standard Deviation 

between Each Subtask and its Matched Baseline ............................................................ 206

Table 84. Mean Speed Standard Deviation Difference Scores for Various Subtasks 

Across Cell Phone Types .................................................................................................. 207

Table 85. ANOVA Results for Within-Subject Comparisons of Headway Standard 

Deviation between Each Subtask and its Matched Baseline ............................................ 208

Table 86. Mean Headway Standard Deviation Difference Scores for Various 

Subtasks Across Cell Phone Types .................................................................................. 209

Table 87. ANOVA Results for Within-Subject Comparisons of Unintentional Lane 

Bust Rate between Each Subtask and its Matched Baseline............................................ 211

Table 88. Mean Unintentional Lane Bust Rate Difference Scores for Various 

Subtasks Across Cell Phone Types .................................................................................. 213

Table 89. ANOVA Results for Within-Subject Comparisons of Peak Deceleration 

between Each Subtask and its Matched Baseline ............................................................ 215

Table 90. Mean Peak Deceleration Difference Scores for Various Subtasks Across 

Cell Phone Types .............................................................................................................. 216

Table 91. ANOVA Results for Within-Subject Comparisons of Mean Speed between 

Each Subtask and its Matched Baseline ........................................................................... 219

Table 92. Mean Speed Difference Scores for Various Subtasks Across Cell Phone Types..... 220

Table 93. ANOVA Results for Within-Subject Comparisons of Mean Headway between 

Each Subtask and its Matched Baseline ........................................................................... 222

Table 94. Mean Headway Difference Scores for Various Subtasks Across 

Cell Phone Types .............................................................................................................. 223

Table 95. ANOVA Results for Within-Subject Comparisons of Mean TTC Between 

Each Subtask and its Matched Baseline ........................................................................... 226

Table 96. Results for Within-Subject Comparisons of SV Lane Change Behavior 

Between Each Subtask and its Matched Baseline ............................................................ 228

Table 97. Results for Between-Subjects Comparisons of SV Lane Change Behavior 

Across Cell Phone Types .................................................................................................. 230

Table 98. Results for Within-Subject Comparisons of SV Right Lane Position 

Between Each Subtask and its Matched Baseline ............................................................ 232

Table 99. Results for Between-Subjects Comparisons of SV Lane Change Behavior 

Across Cell Phone Types .................................................................................................. 233

Table 100. Results for Within-Subject Comparisons of RV Tailgating Behavior 

Between Each Subtask and Its Matched Baseline ............................................................ 236

Table 101. Results for Between-Subjects Comparisons of RV Tailgating Behavior 

Across Cell Phone Types .................................................................................................. 237

Table 102. Results for Within-Subject Comparisons of RV Lane Change Behavior 

Between Each Subtask and Its Matched Baseline ............................................................ 239

Table 103. Results for Between-Subjects Comparisons of RV Tailgating Behavior 

Across Cell Phone Types .................................................................................................. 240

Final Report

xviii 
List of Tables 

Table 104. Exact Odds Ratios for the Emotional Conversation ................................................ 241

Table 105. Frequencies of Observed Intersection Scanning .................................................... 242

Final Report

xix 

List of Figures 

LIST OF FIGURES 

FIGURE 1. MULTIPLEXED IMAGE OF THE FOUR CAMERA VIEWS. TOP LEFT: View of the Driver’s Face. 

TOP Right: View of the Forward Roadway. BOTTOM Left: Over-the-Shoulder View of the 

Driver. BOTTOM Right: View of the Rearward Roadway. (NOTE: Driver Shown Is a VTTI

Researcher.) ....................................................................................................................... 12

Figure 2. Number of Calls During Driving per Driver .................................................................. 20

Figure 3. Number of Calls Made per Hour of Driving Above 8 km/h ........................................... 21

Figure 4. Frequency and Duration for Cell Phone Subtasks When Driving Above 8 km/h ........ 25

Figure 5. Frequency and Duration for Cell Phone Subtasks When Driving Below 8 km/h.......... 26

Figure 6. Frequency and Duration of Talk/Listen Cell Phone Subtask Across Speed Level ...... 27

Figure 7. Percentage of Cell Phone Subtasks With Non-Cell-Phone-Related Secondary 

Task by Cell Phone Type .................................................................................................... 29

Figure 8. SCE Rate per Driver by Gender and Age Group ....................................................... 155

Figure 9. Phone Reaching Locations and Observed Percentages ........................................... 194

Figure 10. Drivers’ Mean Percent TEORT When Initiating a Cell Phone Subtask 

Above 8 km/h .................................................................................................................... 203

Figure 11. Drivers’ Mean TEORT Duration When Initiating a Cell Phone Subtask Above 8 km/h.

 .......................................................................................................................................... 204

Figure 12. Drivers’ Mean Speed Standard Deviation When Initiating a Cell Phone Subtask 

Above 8 km/h .................................................................................................................... 205

Figure 13. Drivers’ Mean Headway Standard Deviation When Initiating a Cell Phone 

Subtask Above 8 km/h ...................................................................................................... 208

Figure 14. Drivers’ Mean Unintentional Lane Bust Rate When Performing a Cell Phone 

Subtask Above 8 km/h ...................................................................................................... 211

Figure 15. Drivers’ Mean Peak Deceleration When Initiating a Cell Phone Subtask 

Above 8 km/h .................................................................................................................... 214

Figure 16. Percentage of Cell Phone Subtask Above 8 km/h where Driver Scanned 

Intersection ........................................................................................................................ 217

Figure 17. Drivers’ Mean Speed When Initiating a Cell Phone Subtask Above 8 km/h ............ 218

Figure 18. Drivers’ Mean Headway When Initiating a Cell Phone Subtask Above 8 km/h ....... 221

Figure 19. Drivers’ Mean TTC When Initiating a Cell Phone Subtask Above 8 km/h ............... 225

Figure 20. Drivers’ Mean Headway When Initiating a Cell Phone Subtask Above 8 km/h ....... 227

Figure 21. Percentage of Samples in which Vehicle Traveled in Right-Most Lane 

When Initiating a Cell Phone Subtask Above 8 km/h ........................................................ 231

Figure 22. Percentage of Samples in which the RV Traveled Closely Behind the SV 

When Initiating a Cell Phone Subtask Above 8 km/h ........................................................ 235

Figure 23. Percentage of Subtasks Performed Above 8 km/h Where the RV Executed a 

Lane Change to Pass the SV ............................................................................................ 238

Figure 24. Drivers’ Mean Trip Time by Location ....................................................................... 242

Final Report

xxi 

Executive Summary 

Executive Summary 

The purpose of this study was to investigate the effects of distraction from the use of three types 

of cell phones while driving: (1) hand-held, (2) portable hands-free, and (3) integrated handsfree. A naturalistic driving study of drivers’ cell phone use was performed. Data was collected 

from 204 drivers who each took part in the study for 31 days (on average) from February 2011 to 

November 2011. Only drivers who reported talking on a cell phone while driving at least once 

per day were recruited. Data acquisition systems in the participants’ own vehicles continuously 

recorded video of the driver’s face, the roadway, and various kinematic data such as the vehicle 

speed, acceleration, range and range rate to lead vehicles, steering, and location. A key feature of 

this study was that participants provided their cell phone records for analysis. This is the first 

NDS to date that combines call and text records with continuous naturalistic driving data. The 

cell phone records allowed the determination of when drivers used their cell phone, while the 

video data allowed the determination of the type of cell phone used, how long it was used for, 

and what subtasks were executed. The result was a rich data set of driver behavior and 

performance when using a cell phone. Three main objectives were then pursued and the results 

are presented below. Exploratory analyses were also performed and the results are presented in 

the report. 

Objective 1: Investigate Drivers’ Cell Phone Use 

It was found that 14,754 calls (28 percent of the calls in the cell phone records) and 8,610 text 

messages (10 percent of the text messages in the cell phone records) overlapped with periods of 

driving. By comparing participants’ cell phone minutes to the recorded driving time, drivers 

were estimated to be talking on a cell phone 10.6 percent of the time. The mean call duration, 

according to the call logs, while driving was 4.02 minutes (Min = 0.08 minutes, Max = 146 

minutes). 

Although drivers were recruited based on self-reports of specific types of cell phone use, video 

inspection was required to confirm the cell phone type used. Approximately 10 percent of all 

calls and 10 percent of all text messages that occurred while driving underwent a video review. 

The exact beginning and end of all cell phone subtasks performed during each call were 

recorded. Driver, vehicle, and environmental factors present at the time were also recorded. This 

data subset provided a comprehensive estimate of drivers’ cell phone use. 

The aggregate cell phone use data were also used to investigate the number of calls made per 

hour of driving. Drivers who had access to PHF cell phones made more calls per minute of 

driving (M = 0.0409) than did drivers who had access to IHF cell phones (M = 0.0296) and 

drivers who had access only to HH cell phones (M = 0.0262). No differences in the number of 

text messages made per minute of driving were found as a function of cell phone type. Note: 

hands-free texting was rare and was not considered in this study. 

Call duration was also assessed as a function of cell phone type. Each call sampled was classified 

into HH, PHF, or IHF cell phone interactions based on the cell phone type used during the 

conversation. When driving at speeds above 8 km/h, drivers talked longer on PHF cell phones 

Final Report

xxiii 
Executive Summary 

(M = 4.96 min) than on IHF cell phones (M = 3.78 minutes) or HH cell phones (M = 3.00 min). 

Again considering driving at speeds above 8 km/h, dialing on an HH cell phone lasted 12.4 s, on 

average, while pushing a button to begin a PHF or IHF call took significantly less time (M = 2.9 

s and 4.6 s, respectively). Note: although it could not be determined whether dialing consisted of 

entering 10 digits or using shortcuts, one reason why the subtask exceeded 12 s was because 

drivers paused to look at the forward roadway. Furthermore, pushing a button to begin an IHF 

call was likely longer than pushing a button to begin a PHF call because the former could include 

visual-manual (VM) interactions with the vehicle’s integrated display. Text messaging lasted 

36.4 s, on average (Min = 0.3 s, Max = 450.1 s). 

Objective 2: Investigate SCE Risk Associated With Cell 

Phone Use 

This study investigated the risk of a safety-critical event associated with using a cell phone. An 

SCE was defined as a crash (where contact was made with another object), a near-crash (where a 

crash was avoided by a rapid evasive maneuver), or a crash-relevant conflict (where a crash 

avoidance response was performed that was less severe than a rapid evasive maneuver, but 

greater in severity than a “normal maneuver”). SCE risk was investigated using two approaches: 

(1) a risk rate approach, which assessed the SCE risk relative to general driving (where non-cellphone secondary tasks could occur), and (2) a case-control approach, which assessed the SCE 

risk relative to “just driving” (where non-driving-related secondary tasks did not occur). For the 

risk rate approach, a risk rate estimate was computed as the number of SCEs during cell phone 

use divided by the total number of minutes spent using a cell phone while driving. This rate was 

then compared to the risk rate of general driving, computed as the number of SCEs during noncell-phone use divided by the total number of minutes driving without cell phone use. A mixed 

effect Poisson regression model was then used to investigate whether the risk rate for cell phone 

use differed from the risk rate for general driving. Risk rate ratios were also computed for 

grouped VM cell phone subtasks as well as for talking/listening subtasks. The results are 

presented in Table 1. Talking on a cell phone was not associated with an increased SCE risk for 

any of the cell phone types. Both call-related and text-related VM subtasks performed on an HH 

cell phone were, however, found to increase SCE risk. As a result, HH cell phone use, collapsed 

across all subtasks, was found to be associated with an increased SCE risk. Pure PHF and IHF 

cell phone use – where VM HH cell phone subtasks are excluded – were not associated with an 

increased SCE risk. It must be noted, however, that 55.5 percent of the sampled PHF 

interactions, and 53.2 percent of the sampled IHF interactions, involved VM HH subtasks. 

Unless stated as pure use, PHF and IHF cell phone use refers to cell phone interactions that could 

involve VM subtasks. 

Final Report

xxiv 
Executive Summary 

Final Report

xxv 

Table 1. SCE Risk Associated With Cell Phone Use as Computed Through Risk Rate 

Approach 

Subtask Rate 

Ratio 

Lower 

Confidence 

Limit 

(LCL) 

Upper 

Confidence 

Limit 

(UCL) 

p-value 

Cell Phone Use – Collapsed 1.32 0.96 1.81 .0917 

Visual-Manual 2.93* 1.90 4.51 < .0001 

 Call-Related Visual-Manual 3.34* 1.76 6.35 .0003 

 Text-Related Visual-Manual 2.12* 1.14 3.96 .0184 

Talking/Listening 0.84 0.55 1.29 .4217 

 Talking/Listening HH 0.84 0.47 1.53 .5764 

 Talking/Listening PHF 1.19 0.55 2.57 .6581 

 Talking/Listening IHF 0.61 0.27 1.41 .2447 

HH Cell Phone Use (Collapsed) 1.73* 1.20 2.49 .0034 

PHF Cell Phone Use (Collapsed) 1.06 0.49 2.30 .8780 

IHF Cell Phone Use (Collapsed) 0.57 0.25 1.31 .1859 

* Indicates a difference at the .05 level of significance 

The risk rate approach generates a powerful estimate of risk by using all accounts of when cell 

phones were used while driving. It is, however, limited in that it cannot assess the SCE risk 

relative to “just driving” (defined as driving void of all non-driving-related secondary tasks) 

without the availability of estimates of the propensity for each potential secondary task that is 

performed concurrently while driving. The case-control approach was thus used to address this 

limitation. A total of 2,308 baseline periods were randomly sampled based on each driver’s 

driving time in the study. This number was selected to be at least four times the 342 SCEs that 

were identified. The odds of an SCE occurring during specific cell phone subtasks were then 

compared to the odds of an SCE occurring when just driving. Note that “just driving” was only 

found in 46 percent of the baseline periods. Table 2 presents the odds ratios and 95-percent 

confidence limits for various cell phone subtasks. As in the previous risk analysis, only VM 

subtasks performed on an HH cell phone were found to be associated with an increased SCE 

risk. Conversing on a cell phone (i.e., any type of cell phone) was not found to increase SCE 

risk. 

Table 2. SCE Risk Associated With Cell Phone Use as Computed Through Case-Control 

Approach 

Subtask OR LCL UCL #SCE 

#Baseline 

periods 

(BL) 

SCE 

Total 

BL 

Total Total 

Cell Phone Use - Collapsed 1.1 0.8 1.53 57 358 211 1426 1637 

Visual-Manual Subtasks 1.73* 1.12 2.69 29 116 183 1184 1367 

 Text Messaging/Browsing 1.73 0.98 3.08 16 64 170 1132 1302 

 Locate/Answer 3.65* 1.67 8 10 19 164 1087 1251 

 Dial 0.99 0.12 8.11 1 7 155 1075 1230 

 Push to Begin/End Use 0.63 0.08 4.92 1 11 155 1079 1234 

 End HH Phone Use 1.26 0.43 3.71 4 22 158 1090 1248 

Talking on Cell Phone 0.75 0.49 1.15 28 259 182 1327 1509 
Executive Summary 

Final Report

xxvi 

Subtask OR LCL UCL #SCE 

#Baseline 

periods 

(BL) 

SCE 

Total 

BL 

Total Total 

 HH Talking 0.79 0.43 1.44 13 114 167 1182 1349 

 PHF Talking 0.73 0.36 1.47 9 86 163 1154 1317 

 IHF Talking 0.71 0.3 1.66 6 59 160 1127 1287 

HH Cell Phone Use 

(Collapsed) 1.39 0.96 2.03 41 204 195 1272 1467 

PHF Cell Phone Use 

(Collapsed) 0.79 0.4 1.55 10 88 164 1156 1320 

IHF Cell Phone Use 

(Collapsed) 0.62 0.26 1.46 6 67 160 1135 1295 

* Indicates a difference at the .05 level of significance 

Objective 3: Investigate Driver Performance When Using a 

Cell Phone 

The third objective of this study was to perform a controlled comparison of driver performance 

when using a cell phone through a within-subject investigation. Each sampled subtask was 

compared to a matched 20-second baseline sample selected 30 s prior to the start of each 

sampled cell phone interaction. Driver, vehicle, and environmental factors were recorded 

similarly to the cell phone samples. One-way within-subject inferential tests were performed to 

assess changes in visual behavior, longitudinal vehicle control, lateral vehicle control, and 

delayed reaction to unexpected external events. Exploratory analyses of the effects of cell phone 

use on driver compensatory behavior, driver lane change performance, driver performance near 

intersections, and downstream traffic behavior were also performed. 

Overall, drivers’ visual behavior was the most sensitive to change when using an HH cell phone. 

VM subtasks such as locating/answering, dialing, text messaging, browsing, and ending the call 

were all found to increase the mean percentage of Total Eyes Off Road Time (TEORT). In 

contrast, the mean percentage TEORT significantly decreased when conversing on an HH cell 

phone. The amount of time drivers’ eyes were off the road was then investigated. Drivers’ mean 

TEORT when text messaging (M = 23.3 s), browsing (M = 8.2 s), and dialing (M = 7.8 s) were 

significantly longer than for locating a cell phone (M = 1.3 s), pushing a button to begin a PHF 

call (M = 0.5 s), pushing a button to begin an IHF call (M = 2.5 s), and ending a call (M = 1.3 s). 

Regarding longitudinal vehicle control, the mean speed standard deviation was found to 

significantly increase from baseline when ending both HH and IHF cell phone use (M = 6.32 

km/h versus M = 4.96 km/h, and M = 5.19 km/h versus M = 3.95 km/h, respectively). Ending 

HH cell phone use was also associated with a significantly higher peak deceleration compared to 

baseline (M = 0.105 g versus M = 0.078 g). Although it is possible that drivers braked harder 

because they were distracted by their cell phone use, it is also possible that drivers chose to end 

their cell phone conversations when coming to a stop (e.g., in their driveway), or when nearing 

their destination (e.g., in a parking lot). Regarding lateral vehicle control, the mean unintentional 

lane bust rate, computed as the number of times the driver unintentionally crossed the lane 

markings divided by the duration of the sample interval, was found to significantly decrease
Executive Summary 

when talking on an HH cell phone (M = 0.001 versus 0.003 lane busts/second). The number of 

unexpected events observed in this study (n = 13) was not enough to perform a statistical 

analysis of delayed driving reaction. 

There were two findings that could be construed as evidence of compensatory behavior when 

using a cell phone. First, browsing was performed at significantly lower speeds than the speeds 

recorded during baseline. Second, text messaging was performed at a significantly greater 

headway than the headways recorded during baseline. It must be noted, however, that the sample 

size pertaining to these findings was quite small, making it difficult to generalize the findings. 

For the most part, drivers did not decrease their speed when performing VM or talking/listening 

cell phone subtasks. Similar results were found when analyzing commercial motor vehicle speed 

when drivers engaged in mobile device use (Fitch & Hanowski, 2012). 

Analyses of drivers’ lane change performance showed that drivers changed lanes significantly 

more often when locating/answering an HH cell phone compared to baseline (10% versus 4%). 

However, the likelihood that drivers used their turn signal when changing lanes was not found to 

differ when using a cell phone. If a lane change was performed, drivers used their turn signal 

during 59 percent of the baseline periods, 52 percent of the VM cell phone subtasks, and 47 

percent of the talking/listening cell phone subtasks. 

The likelihood of properly scanning an intersection was not found to differ when using a cell 

phone. Drivers properly scanned the intersection during 38 percent of the baseline periods, 36 

percent of the grouped VM cell phone subtasks, and 35 percent of the grouped talking/listening 

cell phone subtasks. 

Finally, the likelihood of a trailing vehicle traveling close (within 14 m, which is just over the 

distance between the start of two standard highway lane markings) to the subject vehicle was 

found to significantly increase during cell phone use. A trailing vehicle was observed to be close 

during 6.2 percent of the baseline periods, 9.8 percent of the VM cell phone subtasks, and 12.3 

percent of the talking/listening cell phone subtasks. Although this could be a result of drivers not 

keeping pace when using a cell phone, it could also be because drivers are using their cell phones 

in situations in which vehicles are closer together (e.g., when stopping at an intersection or when 

in stop-and-go traffic). The likelihood of the trailing vehicle passing the subject vehicle was not 

found to change. 

Summary 

The results from this study present a clear finding: VM subtasks performed on HH cell phones 

degrade driver performance and increase SCE risk. Talking on a cell phone, regardless of the 

type of interface, was not associated with an increased SCE risk. Pure PHF and IHF cell phone 

use – where VM HH cell phone subtasks are excluded – were also not associated with an 

increased SCE risk. Although current hands-free (HF) interfaces allow drivers to communicate 

with their voice, there is a concern that they still allow, and sometimes require, VM HH cell 

phone subtasks. Drivers can, and frequently do, initiate HF calls, text/browse during HF calls, 

and end HF calls with an HH cell phone. HF interfaces also require that drivers enable a 

Bluetooth connection, pair their cell phone, and manually dial if their voice commands are not 

recognized. Such VM HH cell phone subtasks detract from the goal of true HF cell phone use. 

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Executive Summary 

Furthermore, there is a segment of the driving population which primarily uses cell phones to 

exchange text messages. Various HF interfaces do not address this type of cell phone use. 

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 Chapter 1: Introduction 

1 Introduction 

The purpose of NHTSA contract DTNH22-11-D-00236, Task Order 5, was to investigate the 

effects of distraction from the use of three types of cell phones while driving: (1) hand-held, (2) 

portable hands-free, and (3) integrated hands-free cell phones. There were three main objectives 

of this study; each was examined using several research questions. 

Objective 1: Investigate Drivers’ Cell Phone Use 

 How do drivers use their cell phones in their vehicles? 

 How does cell phone use differ with cell phone type? 

 How are cell phones used in different traffic environments? 

Objective 2: Investigate Safety-Critical Event Risk Associated With Cell Phone Use 

 What is the SCE risk associated with conversing on a cell phone? 

 What is the relative risk of conversing on an HH, PHF, and IHF cell phone? 

 What is the SCE risk associated with specific cell phone subtasks? 

Objective 3: Investigate Driver Performance When Using a Cell Phone 

 How distracted are drivers while using different types of cell phones? 

 How much distraction is due to different cell phone subtasks? 

 What are the effects of distraction from “just talking” on a cell phone? 

1.1 Study Rationale 

The National Highway Traffic Safety Administration has a long-term goal of eliminating crashes 

attributable to driver distraction. To achieve this goal, a plan was formulated, the first initiative 

of which was to improve the understanding of the extent and nature of the distraction problem 

(NHTSA, 2010). This initiative has predominantly focused on investigating driver distraction 

from cell phone use and served as the primary motivation for the current study. 

There are several reasons to investigate drivers’ cell phone use. They include: 

 Cell phone subscriptions are exponentially increasing 

 Many people use their cell phones while driving 

 Complex cell phone subtasks, such as text messaging, dialing, and locating a cell phone 

are associated with an increased crash risk 

 There are various types of cell phone devices available to drivers 

 Drivers continue to use HH cell phones despite the availability of hands-free (HF) 

technology 

 Some people primarily use their cell phone to send/receive text messages (“text 

messaging”), despite the fact that text messaging while driving has been banned in many 

states 

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 Chapter 1: Introduction 

 There are limited data on the crash risk associated with PHF and IHF cell phones 

Given these concerns, this study set out to characterize drivers’ cell phone use (i.e., calls and text 

messages made with HH, PHF, and IHF cell phones), the SCE risk associated with cell phone 

use, and the impact of cell phone use on driving performance by performing a naturalistic driving 

study (NDS). An NDS data set was generated by installing video cameras and kinematic sensors 

in participants’ own vehicles and continuously recording their driving performance – without an 

experimenter in the vehicle – for an extended period of time. Drivers were not given any specific 

instructions and consequently were expected to behave naturally. Data were collected from 204 

drivers, each of whom took part in the study, on average, for 31 continuous days within the 

overall study period (February 2011 to November 2011). Data acquisition systems (DASs) 

installed in the participants’ own vehicles continuously recorded video of the driver’s face, the 

roadway, and various kinematic data such as the vehicle speed, acceleration, range and range rate 

to lead vehicles, steering, and location. A key feature of this study was that participants provided 

their cell phone records for analysis. No NDS to date has combined call and text records with 

continuous naturalistic driving data. In doing so, the cell phone records allowed an accurate 

determination of when drivers used their cell phone, while the video data allowed an accurate 

determination of the type of cell phone used, how long it was used for, and what subtasks were 

executed. The end result was a rich data set of driver behavior and performance when using a 

cell phone. 

Final Report

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 Chapter 2: Background 

2 Background 

Driver distraction has been defined as the diversion of attention from activities critical for safe 

driving towards a competing activity (US-EU Bilateral ITS Technical Task Force, 2010). It is a 

behavior that jeopardizes the safety of drivers, passengers, and non-occupants alike. In 2010, 

3,092 people were killed (9 percent of all fatal crashes), and 416,000 people were injured (18 

percent of all injury crashes), in crashes involving distracted drivers (NHTSA, 2012). 

2.1 Driver Distraction From Cell Phone Use 

Of the 3,092 people killed in distraction-affected crashes, 408 (13%) occurred in crashes in 

which at least one of the drivers was using a cell phone at the time of the crash (NHTSA, 2012). 

Using a cell phone can take many forms, each imposing various levels of distraction. 

Traditionally, conversing has been the primary form of cell phone use. This activity, however, 

requires several visual-manual subtasks to initiate and end cell phone use. VM subtasks are a 

concern because they require drivers to take their eyes off the road and their hands off the 

steering wheel to be performed. Newer cell phone interfaces have been designed to simplify use 

by allowing drivers to initiate and end calls with voice commands or with a single button press. 

In doing so, however, it has become easier for drivers to read and browse using their HH cell 

phone while simultaneously conversing using HF technology. Furthermore, despite best efforts 

to redesign how drivers interact with cell phones, there is a growing subset of the population 

whose primary goal of cell phone use is text messaging. Text messaging is a considerable 

concern because it imposes distraction that exceeds the VM subtasks inherent to making and 

ending calls (Olson, Hanowski, Hickman, & Bocanegra, 2009). To understand the distraction 

that cell phones impose on drivers, it is imperative to take a hierarchical task analysis approach 

so that the effects of different types of subtasks can be quantified. Doing so will provide a clearer 

perspective on drivers’ cell phone use, the risk associated with using a cell phone, and drivers’ 

performance when using a cell phone. 

2.1.1 Drivers’ Cell Phone Use 

Cell phone subscriptions have increased exponentially since their introduction in the 1980s. The 

number of subscriptions has surpassed the U.S. population (International Telecommunications 

Union, 2011). Their prevalence amongst younger and less experienced drivers has also 

dramatically increased (Lenhart, Ling, Campbell, & Purcell, 2010). Quantifying how much 

drivers use their cell phones is an essential first step to understanding their impact on 

transportation safety. 

The National Occupant Protection Use Survey (NOPUS) estimates that, in 2010, drivers used an 

HH cell phone 5 percent of the time (Pickrell & Ye, 2011). Furthermore, the percentage of 

drivers who were text-messaging or visibly manipulating HH devices was 0.9 percent. These 

estimates were generated by a nationwide probability-based observational survey, where drivers’ 

electronic device use when stopped was observed at randomly selected controlled intersections 

throughout the United States. In applying the hands-free to hand-held cell phone ratio observed 

in NHTSA’s 2007 Motor Vehicle Occupant Safety Survey (MVOSS) to the NOPUS findings, 

Final Report 

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 Chapter 2: Background 

NHTSA estimates that 9 percent of drivers were using either an HH or HF cell phone while 

driving at a typical daylight moment in the United States in 2010 (Pickrell & Ye, 2011). 

Drivers’ cell phone use has also been estimated using NDS data sets. Fitch and Hanowski (2011) 

estimated drivers’ cell phone use by examining the frequency of cell phone subtasks in both 

light- and heavy-vehicle NDS data sets. The light-vehicle data set was generated by the 100-Car 

Study, which collected data from 241 drivers in the Northern Virginia area from January 2003 to 

July 2004 (Klauer, Dingus, Neale, Sudweeks, & Ramsey, 2006). The heavy-vehicle data set 

comprised data from two commercial motor vehicle NDSs that collected data from May 2004 to 

May 2005, and from November 2005 to May 2007 (Olson, Hanowski, Hickman, & Bocanegra., 

2009). Light-vehicle drivers were estimated to have used a cell phone (i.e., dial, talk on an HH 

cell phone, or talk on an HF cell phone) 8.3 percent of the time the vehicle was in motion (i.e., 

traveling at 24 km/h or faster). These drivers dialed 1.0 percent of the time, conversed on an HH 

cell phone 6.2 percent of the time, and conversed on an HF cell phone 1.3 percent of the time. 

Similarly, commercial vehicle drivers were estimated to have used a cell phone 9.2 percent of the 

time the vehicle was in motion (i.e., traveling at 8 km/h or faster). These drivers dialed on the 

cell phone 1.0 percent of the time, conversed on an HH cell phone 4.2 percent of the time, 

conversed on an HF cell phone 4.1 percent of the time, and texted 0.1 percent of the time. Note 

that text messaging was not observed in the 100-Car Study because it was not a widespread 

method of communication when the data were collected. 

Complementing these estimates, a study that analyzed the naturalistic driving data collected from 

light vehicles in the Integrated Vehicle-Based Safety System Field Operational Test estimated 

that drivers used their cell phone 6.7 percent of the time the vehicle was in operation (both 

stopped and in motion) (Funkhouser & Sayer, 2012). Drivers conversed on an HH or HF cell 

phone 6.7 percent of the time, and performed VM HH cell phone subtasks 2.3 percent of the 

time. These estimates were produced by examining every minute of driving data collected from 

the drivers’ first week of driving in the study. These data were collected in 2006. This study 

showed that drivers used a cell phone more frequently when the vehicle was stopped compared 

to when it was in motion. Drivers conversed on an HH or HF cell phone 7.2 percent of the time, 

and performed VM HH cell phone subtasks 2.8 percent of the time, when stopped; while they 

conversed on an HH or HF cell phone 5.9 percent of the time, and performed VM HH cell phone 

subtasks 1.9 percent of the time, when moving (Funkhouser & Sayer, 2012). 

2.1.2 Crash Risk of Using a Cell Phone 

A central component of the NHTSA distraction plan’s first initiative is to understand the crash 

risk of using a cell phone. Early epidemiological research reported that using a cell phone – be it 

HH or HF – is associated with a quadrupling of the risk of injury and property damage crashes 

(McEvoy et al., 2005; Redelmeier & Tibshirani, 1997). However, a series of NDSs that 

investigated the risk of drivers performing specific cell phone subtasks unanimously found that 

SCE risk was associated with complex subtasks such as text messaging and dialing; in contrast, 

conversing on a cell phone was not associated with an increased crash risk (Hickman, Hanowski, 

& Bocanegra, 2010; Klauer, Dingus, Neale, Sudweeks, & Ramsey, 2006; Olson, Hanowski, 

Hickman, & Bocanegra, 2009). These results were observed for both commercial motor vehicle 

and light-vehicle drivers, as well as across broad classifications of low, moderate, and high 

driving task demands (Fitch & Hanowski, 2011). These results suggest that: (1) the relative risks 

Final Report 

4 
 Chapter 2: Background 

of different cell-phone-use subtasks are not equivalent (Hanowski, 2011), and (2) knowing what 

subtask was executed by the driver prior to a crash is necessary when assessing the risk 

associated with cell phone use. 

It is important to note that the SCE risk of cell phone use – when collapsing across subtasks – 

estimated in the NDS investigations has never been near the fourfold increase reported in the 

earlier epidemiological studies. This inconsistency is compounded by a more recent 

epidemiological study that found that the risk of an airbag crash associated with HF conversation 

was moderately low (Young & Schreiner, 2009). Dingus, Hanowski, and Klauer (2011) 

speculate that that this was because the earlier epidemiological studies were unable to precisely 

know what the driver was doing just prior to the crash. As such, the drivers could have 

completed their cell interactions up to 10 minutes prior to having to react to a crash 

circumstance. Additionally, the drivers could have performed a number of tasks with the cell 

phone, only one of which was a conversation. Young (2011) presents a resolution to this 

discrepancy. By investigating drivers’ exposure to driving, he estimates that the two 

epidemiological studies mentioned above may have actually had less driving time in their control 

window on the day before the crash, than in the window just before the crash. This bias may be 

why they overestimated the relative risk for cell phone use while driving. In correcting for 

drivers’ exposure, Young found that the relative risk for cell phone use reported in the previous 

epidemiological studies lowered to about 1.0, aligning the estimates with the findings from the 

NDSs. Note: a relative risk of 1.0 means that there is no difference in risk between using a cell 

phone while driving and not using a cell phone while driving. 

The risk associated with talking on a cell phone is of great interest because it comprises the 

majority of cell phone use. Previous NDSs have not found SCE risk to be significantly elevated 

by cell phone conversation. Some NDSs even found that commercial motor vehicle drivers were 

at a decreased risk when conversing on an HF cell phone (Hickman, Hanowski, & Bocanegra, 

2010; Olson, Hanowski, Hickman, & Bocanegra, 2009). In contrast, non-NDS research has 

found that driving performance degrades when concurrently conversing on a cell phone (Atchley 

& Dressel, 2004; Drews, Pasupathi, & Strayer, 2004; Horrey, Lesch, & Garabet, 2008; Strayer, 

Drews, & Johnston, 2003). As such, an investigation of the SCE risk associated with talking on a 

cell phone using current data is required. 

2.1.3 Driver Performance When Using a Cell Phone 

Driver performance when using a cell phone has been investigated in previous NHTSA research 

(Angell et al., 2006; Klauer, Dingus, Neale, Sudweeks, & Ramsey, 2006; Ranney, Baldwin, 

Parmer, Martin, & Mazzae, 2011). Performance measures have included drivers’ visual behavior, 

longitudinal vehicle control, lateral vehicle control, and reaction time to unexpected events. 

Using a cell phone requires numerous subtasks to be executed (e.g., locating/reaching for the 

device, dialing a number, talking/listening, and ending the call). Each subtask involves different 

types and levels of distraction. As such, the degree to which each subtask affects driving 

performance is of significant interest. 

Reaching for a cell phone, dialing, browsing, and text messaging can be classified as complex 

subtasks because they require the driver to take his/her eyes off the road for an extended period 

of time. For instance, drivers have been found to take their eyes off the road for 4.6 seconds over 

Final Report 

5 
 Chapter 2: Background 

a 6-second interval when text messaging (Olson, Hanowski, Hickman, & Bocanegra, 2009). 

When traveling at a speed of 90 km/h, this equates to a driver traveling the length of a football 

field without looking at the roadway. Furthermore, when drivers’ eyes are off the road, the 

longitudinal vehicle control, lateral vehicle control, and the ability to detect unexpected events 

degrade. Consequently, measuring where drivers look when interacting with a cell phone is 

essential to understanding how cell phone use affects driver performance. 

Although the disruption on driving performance from talking on a cell phone has been 

consistently shown to be less than that which is seen for VM subtasks (Ranney, Baldwin, 

Parmer, Martin, & Mazzae, 2011), controlled experimentation using driving simulators and test 

tracks have shown that conversing on a cell phone can negatively affect driving performance. 

Conversing on a cell phone has been linked to: 

 Increases in drivers’ ratings of workload (Horrey, Lesch, & Garabet, 2009); 

 Missed signals and slower reaction times (Strayer & Johnston, 2001); 

 Poor speed maintenance and headway distance (Rakauskas, Gugerty, & Ward, 2004); 

 Instances when drivers look but fail to remember seeing objects (Strayer, Drews, & 

Johnston, 2003); 

 Reductions in the area that drivers scan (Atchley & Dressel, 2004; Maples, DeRosier, 

Hoenes, Bendure, & Moore, 2008); 

 Increases in reaction times to unexpected events (Caird, Willness, Steel, & Scialfa, 2008; 

Horrey & Wickens, 2006) 

 Decreases in travel speed (Cooper, Vladisavljevic, Strayer, & Martin, 2008; Young, 

Regan, & Hammer, 2003) 

 Increases in following distance (Cooper et al., 2008) 

 Lower lane change frequencies (Cooper et al., 2008) 

 Missed navigational signage (Drews, Pasupathi, & Strayer, 2004) 

 Increases in stop light violations when in an intersection dilemma zone (Horrey, Lesch, & 

Garabet, 2008) 

At the same time, there is some evidence that conversing on a cell phone can raise alertness in 

monotonous driving conditions. A field study found that drivers that received regularly 

scheduled phone calls were more alert and awake during the conversation and up to 20 minutes 

afterwards (Jellentrup, Metz, & Rothe, 2011). Given these findings, a controlled investigation of 

the degree to which driver performance is affected by cell phone use using representative data is 

required. 

Final Report 

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 Chapter 2: Background 

2.2 Designing to Mitigate Distraction From Cell Phones 

A logical progression from previous research findings on driver distraction has been to minimize 

the need for complex subtasks when interacting with any kind of interface while driving. In the 

context of cell phones, wired headsets were one of the first attempts at this design goal by 

allowing drivers to converse without holding a cell phone to their ear. Headsets and earpieces 

that wirelessly connect to the cell phone were later released to achieve the same purpose more 

conveniently. Speakerphone devices (either built into the cell phone or wirelessly-connected) are 

also available in the marketplace. These types of devices form a category which has been termed 

portable hands-free (PHF) cell phones in this study. Note, speakerphones that continue to be held 

during use are still considered HH cell phones in this study. 

Although PHF cell phones allow drivers to keep their hands on the steering while conversing, 

they still require drivers to physically manipulate a device. When using the cell phone, drivers 

may have to reach for the headset/earpiece, or put it away after use. These subtasks have the 

potential to distract drivers. Although it is recognized that the ideal use of PHF cell phones is to 

handle the headset/earpiece when the vehicle is stopped, such interactions are possible while the 

vehicle is in motion. 

A design alternative is to integrate the cell phone with the vehicle. Equipment comprising 

microphones, speakers, steering wheel push buttons, and voice recognition software installed in 

the vehicle by the manufacturer enables all cell phone subtasks to be performed while the driver 

keeps his/her eyes on the road and hands on the steering wheel. Such systems are termed 

integrated hands-free (IHF) cell phones in this study. Research has shown that voice control of 

in-vehicle devices may allow drivers to keep their eyes on the road longer, track their course 

more consistently, and have lower mental demand than when these devices are controlled 

manually (Owens, McLaughlin, & Sudweeks, 2010). However, having IHF systems available 

does not guarantee that drivers will use them, and physical manipulation of cell phones to initiate 

and end calls remains possible. Potential concerns include: (1) drivers manipulating an HH cell 

phone while engaged in an IHF conversation, and (2) drivers interacting with integrated touchscreen displays to initiate and end cell phone use. 

Given the findings on HH and HF cell phone use, as well as the widespread availability of newer 

HF interfaces, NHTSA is focused on improving the understanding of how cell phone use, and its 

inherent subtasks, distracts drivers and jeopardizes safety. This study was designed to quantify 

drivers’ cell phone use, assess the risk of an SCE associated with such use, and investigate its 

effect on driver performance. The analysis of in situ driver behavior data collected through a 

large-scale NDS supports the generalization of results to real-world driving conditions. 

Final Report 

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 Chapter 3: Methods 

Final Report 

9 

3 Methods 

3.1 Driver Demographics 

Data collected from 204 drivers in a previous contract (NHTSA contract DTNH22-05-D-1002) 

were analyzed in this study. There were 129 females (63%) and 75 males (37%) with a median 

age of 41 years (18 to 84 years). Drivers were recruited if they reported using a cell phone at 

least once per day while driving. Drivers were assigned to one of three cell phone groups (HH, 

PHF, and IHF) if they reported using one type of cell phone at least 50 percent of the time (see 

Table 3 for an operational definition of each type of cell phone). The assigned groupings, 

however, were not used in the data analysis. This is because the type of cell phone used in a 

given interaction could be different from the type of cell phone the driver reported using the 

majority of the time (e.g., drivers in the IHF group could make calls using HH cell phones). 

Inspection of the recorded video was thus required to verify the type of cell phone used. The 

initial group assignments were used to help ensure that a representative sample of each cell 

phone type was collected. The distribution of the participants by assigned cell phone type and 

location are shown in Table 4. The reader is referred to section 4 (Investigation of Drivers’ Cell 

Phone Use) which describes how cell phone use was analyzed as HH, PHF, or IHF based on the 

cell phone type used in the conversation. 

Table 3. Definition of Cell Phone Type Used in Recruiting Drivers 

Cell Phone Type Operational Definition 

Hand-Held (HH) 

All cell phone subtasks including reaching, dialing, and talking are performed on an HH 

phone. This included holding the cell phone while its built-in speakerphone feature was 

enabled. Note: using the speakerphone feature while the cell phone was not held constituted 

PHF cell phone use. 

Portable HandsFree (PHF) 

Refers to instances when some cell phone subtasks, including reaching, dialing, and talking 

were performed with a PHF device. PHF devices included headsets (wired or wireless) or 

other aftermarket Bluetooth or hands-free devices that were not integrated into the vehicle by 

the manufacturer. PHF did include voice activation performed through the PHF device. 

Integrated HandsFree (IHF) 

Refers to when some cell phone subtasks, including reaching, dialing, and talking, were done 

with a cell phone technology that was integrated into the vehicle. This included equipment 

installed by the vehicle manufacturer such as microphones and speakers for cell phone use, a 

speech-based user interface to dial the phone, and other phone controls built into the vehicle 

(e.g., center stack and/or steering wheel buttons). IHF included both vehicles that had a cell 

phone built into the vehicle itself, and vehicles that detected and interacted with the user’s 

portable device without requiring direct manipulation of the phone itself. 

Table 4. Distribution of Participants by Cell Phone Usage Group and Location 

HH PHF IHF Total 

Northern Virginia 31 34 31 96 

Southern Virginia 34 35 22 91 

North Carolina 0 0 17 17 

Total 65 69 70 204 
 Chapter 3: Methods 

Final Report 

10 

Drivers in each group were recruited from rural and urban/suburban locations. Originally, half of 

the sample was to be recruited from the Blacksburg/Roanoke region of Virginia, which included 

rural, suburban, and light urban roads. The remaining half was to be recruited from the Northern 

Virginia suburbs outside of Washington, DC. However, toward the end of the study, a third site 

was introduced – the Raleigh/Durham region of North Carolina – due to the difficulty of 

recruiting drivers of vehicles equipped with IHF cell phones. State laws in North Carolina were 

similar to Virginia with regard to cell phone use by drivers. One difference, however, is that 

North Carolina has a primary law banning text messaging (but not HH calls), while Virginia had 

a secondary law banning text messaging. Note: some drivers in Northern Virginia drove in 

Washington, DC, where there was a primary law banning text messaging and all other HH cell 

phone use. Some also drove in Maryland, where there is also a primary law banning text 

messaging. Table 5 summarizes the state laws in effect at the time of data collection. These laws 

are reviewed because they may have affected drivers’ willingness to engage in cell phone use, 

and/or affected how they used the cell phone. 

Table 5. Summary of State Cell Phone Laws 

State/District Cell Phone Laws 

Virginia 

 Ban on all cell phone use (HH and HF) for bus drivers (Primary law) 

 Ban on all cell phone use (HH and HF) for novice drivers (Primary law) 

 Ban on text messaging for all drivers (Secondary law; Primary law for bus drivers) 

Washington, 

DC 

 HH ban for all drivers (Primary law) 

 Ban on all cell phone use (HH and HF) for bus drivers (Primary law) 

 Ban on all cell phone use (HH and HF) for novice drivers (Primary law) 

 Ban on text messaging for all drivers (Primary law) 

Maryland 

 HH ban for all drivers (Secondary law) 

 Ban on all cell phone use (HH and HF) for novice drivers (Secondary law) 

 Ban on text messaging for all drivers (Primary law) 

North Carolina 

 Ban on all cell phone use (HH and HF) for bus drivers (Primary law) 

 Ban on all cell phone use (HH and HF) for novice drivers (Primary law) 

 Ban on text messaging for all drivers (Primary law) 

Source: NHTSA, 2012b 

Participants were eligible for inclusion in the study if they met all of the following criteria: 

 Lived in Virginia or North Carolina, had a valid driver’s license, and were at least 18 

years old; 

 Owned an eligible vehicle – this included vehicle models that had a vehicle network that 

was compatible with the DAS; 

 Were the primary driver of the vehicle (vehicle was seldom driven by anyone else); 

 Reported using their cell phone at least once per day while driving (preference was given 

to those who reported more cell phone use); 

 Reported that, while driving, they used their cell phone at least 50 percent of the time by 

one of the three types of cell phones; 

 Reported driving at least 4-5 days per week; 
 Chapter 3: Methods 

 Reported driving at least 50-99 miles per week; and 

 Indicated willingness to provide cell phone records for those calls completed during the 

study period. 

Recruitment involved typical media outlets (e.g., newspapers, Craigslist). However, additional 

methods were used to target drivers who used IHF cell phones because their numbers were fewer 

than drivers of the other cell phone types. These additional methods included placing flyers on 

eligible vehicles in parking lots and word of mouth. All recruiting materials described the study 

as a driver safety study that used monitoring technology, but did not mention cell phones 

specifically. Interested individuals were screened for eligibility by phone. 

All study protocols were approved by the Virginia Tech and Westat Institutional Review Boards. 

Participating drivers read and signed an informed consent form and received $300 for their 

participation. One hundred dollar payments were made three times during the study: (1) after the 

participant’s vehicle was prepared for the study and the paperwork was completed, (2) after the 

equipment was removed from the participant’s vehicle and a discussion on the driver’s 

experiences with the system took place, and (3) once the participant’s cell phone records for the 

weeks of participation were received. Participants that did not provide their cell phone records 

did not receive the final $100. 

3.2 Data Collection 

The DAS used in the study was based on the data collection platform used for naturalistic driving 

measurement in the Strategic Highway Research Program 2 (SHRP2) NDS overseen by the 

Transportation Research Board (, 2008). The platform had the same basic components and 

functionality, but with some additions and modifications to meet the needs of the current study. 

The following data elements were captured by the DAS. 

 Video was captured using four in-vehicle cameras (Figure 1). One camera captured the 

driver’s face and torso, with a partial view out the driver’s side window. This view was 

used to identify cell phone subtasks (e.g., reaching, dialing, conversing, and text 

messaging) and the drivers’ eye glance locations. A second camera captured a wide-angle 

view of the forward roadway. This view was used to identify the driving context (e.g., 

road type, traffic density, and weather) and observe SCEs. A third camera captured video 

of the vehicle’s console and controls. This view was used to observe the driver’s 

interaction with the vehicle controls, including IHF controls, whether the driver’s hands 

were on the steering wheel, and cell phone subtasks performed near the driver’s lap (e.g., 

text messaging or browsing). A fourth camera captured video of the rearward roadway. 

This view was used to identify tailgating and whether the trailing vehicle passed the 

subject vehicle. 

Final Report 

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 Chapter 3: Methods 

Figure 1. Multiplexed image of the four camera views. Top left: view of the driver’s face. 

Top right: view of the forward roadway. Bottom left: over-the-shoulder view of the driver. 

Bottom right: view of the rearward roadway. (Note: Driver shown is a VTTI researcher.) 

 Accelerometers in the vehicle were used to detect large longitudinal and lateral forces 

that might indicate risky driving, as well as near-crash and crash events. 

 Global Positioning System technology indicated the vehicle’s location. The GPS device 

also recorded a standard time signal, which was used to synchronize the DAS data with 

the driver’s cell phone records. 

 Forward Radar was used to monitor the area in front of the SV and was used to 

determine the presence of other vehicles or objects. By comparing vehicle speed and 

changes in object distances, the RADAR was used to provide measures of unsafe 

headways, times-to-collision, and near-collisions. 

 Lane Tracker Machine Vision was used to estimate the vehicle’s distance to existing lane 

markings. Output from this sensor was used by reductionists to identify lane busts. 

 Illuminance Sensor was used to monitor the ambient light. This sensor helped 

reductionists identify the prevalent illumination conditions. 

 Vehicle Network Data From the On-Board Diagnostics (OBD-II) Port was used to 

monitor other vehicle measures such as vehicle speed, brake application, and steering 

wheel position. 

Appendix A1 summarizes the data elements collected by the DAS and the associated dependent 

measures captured by these elements. It should be noted that audio data were not collected in this 

study. 

DAS installation took approximately 3 to 4 hours, and was completed by trained vehicle 

technicians. After installation, participants were instructed to drive as they normally would for a 

period of four weeks. Past experience indicated that participants in vehicle monitoring studies 

Final Report 

12 
 Chapter 3: Methods 

tend to act naturally after an adjustment period of a few hours (Lee, Dingus, Klauer, Neale, & 

Sudweeks, 2005). No data was omitted from the analysis based on this adjustment period. 

The project team monitored the recorded data to ensure that the systems were functioning 

properly. Other than to schedule a system removal date, the project team did not interact with 

participants during the monitoring period, unless there was a problem with the data collection 

equipment, which occurred infrequently. At the end of the monitoring period, the data collection 

system was removed from the participant’s vehicle. Researchers then worked with participants to 

acquire their cell phone records encompassing their period of participation. 

3.3 Data Reduction 

The following sections provide an overview of the data reduction process. Additional details are 

contained in Appendixes A2 to A9. 

3.3.1 Cell Phone Records 

The cell phone records were manually entered into an electronic spreadsheet by data 

reductionists. The call records listed the date and start-time of the call, the duration of the call 

rounded up to the nearest minute, the direction of the call (sent /received), and the service 

provider. The text records listed the date and time the text message was exchanged, the direction 

of the text message, and the service provider. The data set was inspected for data entry errors. 

Corrections were made when they were found. Although rare, cases in which drivers 

simultaneously used two phones, or used a secondary phone whose records were not provided, 

did occur. 

A total of 191 of the 204 drivers provided their cell phone records (94%). One driver had records 

that did not overlap driving, 3 drivers had calls that were prior to, or at the end of, driving, and 

187 drivers (92%) had calls placed/received while driving. A total of 121 drivers (59%) provided 

text records; 109 drivers (53%) had text messages sent/received while driving. A total of 51,725 

calls and 82,950 text messages were in the cell phone records. While available for some drivers, 

the cell phone data use records were not used in the study (e.g., to identify Internet browsing) 

because phones have applications that transmit data while running in the background without 

driver intervention. 

Table 6 lists the cell phone providers with which participants had cell phone subscriptions, the 

number of drivers that subscribed to each cell phone provider, and the cell phone providers’ 

billing policy. More information on the cell phone provider billing policies can be found in 

Appendix A2. 

Final Report 

13 
 Chapter 3: Methods 

Final Report 

14 

Table 6. Cell Phone Provider Billing Policies 

Cell Phone Provider Number of Participants 

Subscribed to Provider Percent (%) Billing Policy 

VERIZON 111 54.4 Round up to the nearest minute 

AT&T 38 18.6 Round up to the nearest minute 

SPRINT 32 15.7 Round up to the nearest minute 

US Cellular 10 4.9 Round up to the nearest minute 

T-MOBILE 7 3.4 Rounds up and down to nearest minute 

Ntelos 2 1.0 Round up to the nearest minute 

BOOST M. 1 0.5 Round up to the nearest minute 

Cricket 1 0.5 Round up to the nearest minute 

Unspecified 2 1.0 

Total 204 100 

3.3.2 Driver Verification 

Each file recorded by the DAS was reviewed by a reductionist to verify that the participant was 

indeed operating the vehicle. Data recorded from non-participating drivers were excluded from 

any further reduction or analysis. 

3.3.3 Trip Summary 

A trip summary file was prepared that listed each file recorded by the DAS, its start and end 

times, the date the file was recorded, the data-collection location where the file was recorded, 

and the de-identified driver ID. A total of 31,562 files were recorded. 

3.3.4 Cell Phone Use While Driving 

The cell phone records were merged with the trip summary data set to generate a data set of all 

files where: 

 The call began after the start of the file, and ended before the end of the file. 

 The call began after the start of the file, and ended after the end of the file. 

 The call began before the start of the file, and ended before the end of the file. 

A total of 14,754 calls and 8,610 text messages were exchanged while the vehicles were in 

operation (i.e., the ignition was turned on). 

To identify how drivers were specifically using their cell phones while driving, 10 percent of the 

calls, with a minimum of four calls per driver, were randomly sampled. Likewise, 10 percent of 

the text messages, with a minimum of four text messages per driver, were randomly sampled. 

Since start time and duration of calls were rounded to the nearest minute, calls in the log that 

occurred at the same time were omitted from computations of the amount of time drivers 

conversed on the phone while operating their vehicle. Duplicate calls were not omitted from any 

frequency computations, however. The same approach was used for text messages. A total of 

1,564 calls and 844 text messages that occurred when the vehicles were in operation were 

sampled. This comprised a total of 2,408 cell phone use samples. 
 Chapter 3: Methods 

Final Report 

15 

Because the large majority of cell phone records were rounded up (one cell phone provider 

rounded down) to the nearest minute, the exact start and end time of each sampled call and text 

had to be identified by viewing the video data. Furthermore, since the records only listed the time 

and direction of the calls, the type of cell phone used to make the call also had to be visually 

determined (via video review). Each sample was reviewed in a customized data reduction 

software application by a team of data reductionists. Samples were omitted if: (1) the video was 

not available, (2) the wrong driver was present, (3) a passenger was the individual using the cell 

phone, (4) the video footage ended just before the cell phone interaction began, or (5) the video 

footage began just after the cell phone interaction ended. A total of 2,108 cell phone samples 

remained. Reductionists then recorded the exact start and end frame for every cell phone subtask 

pertaining to the sampled interaction. The following cell phone subtasks were recorded (Table 

7). Operational definitions for each subtask are presented in Appendix A3. 

Table 7. Subtasks Reduced 

Subtask Abbreviation 

Hand-Held: Locate/Reach/Answer HH: Locate/Answer 

Hand-Held: Dialing HH: Dial 

Hand-Held: Talk/Listen/Voice Commands HH: Talk/Listen 

Hand-Held: Text Messaging HH: Text 

Hand-Held: Viewing/Browsing/Reading HH: Browse/Read 

Hand-Held: End Task HH: End Task 

Hand-Held: Holding HH: Hold 

Portable Hands-Free: Locate/Put-on Headset/Earpiece PHF: Locate/Put on 

Portable Hands-Free: Push Button to Begin/Answer PHF: Begin/Answer 

Portable Hands-Free: Talk/Listen/Voice Commands PHF: Talk/Listen 

Portable Hands-Free: Push Button to End PHF: End Task 

Portable Hands-Free: Holding/Wearing Headset/Earpiece PHF: Hold/Wear 

Integrated Hands-Free: Press Button to Begin/Answer IHF: Begin/Answer 

Integrated Hands-Free: Talk/Listen/Voice Commands IHF: Talk/Listen 

Integrated Hands-Free: Press Button to End IHF: End Task 

Cell Phone Navigation Navigation 

Other Cell Phone Task Other 

To clarify terminology used in this report, a cell phone subtask refers to a specific action the 

driver takes when using a cell phone (such as dialing), while a cell phone interaction refers to the 

series of subtasks that took place during the sampled call or text. The start and end points of the 

subtasks bounded the data reduction performed on them. However, because talking on a cell 

phone could be a lengthy subtask, only a random 6-second interval of the talking subtask was 

selected for further reduction. Care was taken to ensure that talking was the only cell phone 

subtask that took place in the sample. Furthermore, any holding of the cell phone or wearing of a 

PHF headset/earpiece that lasted longer than 5 s was treated as a separate subtask. Similarly to 

talking on a cell phone, a random 6-second interval was sampled since this subtask could also be 

quite long in duration. If the holding subtask lasted longer than 30 s, then the search for the 

beginning or end of the subtask was halted. 

It was found that some cell phone interactions involved numerous combinations of cell phone 

subtasks. As such, only the first occurrence of each subtask combination was advanced for 

further data reduction. Therefore, if a cell phone interaction consisted of the driver: (1) pushing a 
 Chapter 3: Methods 

Final Report 

16 

button on his Bluetooth earpiece to begin a PHF cell phone call, (2) talking using the PHF 

earpiece, (3) browsing the HH cell phone during the PHF conversation, (4) putting the HH cell 

phone down and continuing to talk for another minute, (5) browsing the HH cell phone again 

during the conversation, (6) putting the HH phone down again and continuing to talk for another 

minute, and (7) pushing a button on the earpiece to end the call, then only the first browsing 

while talking subtask combination would be selected for reduction. For each sampled subtask, 

reductionists answered 49 questions pertaining to the driver, vehicle, and environmental factors 

present. These parameters are listed in Appendix A4. Reductionists also recorded the drivers’ 

eye glance locations over the span of each subtask. Eye glance locations were recorded at 10 Hz 

(Appendix A5). 

Kinematic data recorded at the time of each subtask were queried from the data set. The list of 

variables that were considered is presented in Appendix A6. 

3.3.5 Cell Phone Use Baseline Periods 

To investigate driver performance when using a cell phone, a 20-second baseline was sampled 

30 s prior to the start of the first VM subtask that was contiguous to the sampled call. To be 

considered contiguous, the subtask had to occur within 30 s of the sampled call. For example, if 

the driver reached for the cell phone and dialed within 30 s of reaching, then the baseline was 

sampled 30 s prior to reaching for the cell phone. However, if the driver reached for the cell 

phone and held it for more than 30 s before dialing, then the baseline was sampled 30 s before 

the dialing subtask. It was important to select baseline periods that were close in time to the 

sampled cell phone use so that the environmental contexts remained similar. A higher degree of 

experimental control was gained as a result. It should be noted that, despite this sampling 

strategy, analyses in this study did not include baseline periods in which the driver used a cell 

phone (including holding a cell phone or PHF headset/earpiece). As such, some cell phone 

interactions could not be analyzed in the within-subject tests performed. 

3.3.6 SCE Identification 

SCEs were identified in this study as follows. First, algorithms developed and validated in 

previous NDSs (Blanco et al., in press; Dingus et al., 2006; Fitch et al., 2012; Hanowski et al., 

2005; Simons-Morton, Ouimet, Zhang, Klauer, & Lee, 2011) were applied to the data set to 

trigger potential SCEs. An additional highway acceleration trigger was developed to identify less 

severe braking that took place at higher speeds. This was done because decelerations of less than 

-0.3 g performed above 64 km/h can still be indicative of unsafe driving. The algorithms’ logic is 

presented in Table 8. 

Table 8. Algorithm Logic Used to Trigger Potential SCEs 

Trigger Algorithm 

Longitudinal Acceleration Longitudinal Acceleration ≤ -0.65 g 

Highway Acceleration Longitudinal Acceleration ≤ -0.3 g and Subject Vehicle Traveling above 64 km/h 2 

seconds beforehand 

Lateral Acceleration Lateral Acceleration ≥ |0.75| g 

Forward Time-to-Collision 

(TTC) 

Forward TTC < 2 s combined with criteria to ensure a stable radar target 
 Chapter 3: Methods 

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17 

Swerve 

Angular acceleration ≥ 10 deg/s2 or 

Yaw changes from at least ±8 deg/s to at least ±8 deg/s (opposite) within 0.75 

seconds

These algorithms triggered 5,754 potential events. Reductionists then visually inspected each 

triggered event to verify whether it comprised an SCE. An experienced reductionist then verified 

each validated event. The experienced reductionist was selected because she had worked on 

numerous NDS data reductions, specifically SCE validation and conflict scenario reduction. 

Table 9 shows the number of triggered events generated by each trigger and the number of valid 

SCEs each one produced. SCEs that were observed upon video inspection, but were not triggered 

by any of the algorithms, were classified as “Analyst Identified.” Reductionists were free to view 

as much video data around the events as needed in order to develop an understanding of the 

context. Triggered events were invalid if the algorithms returned a false alarm or lacked a 

conflict that required a rapid evasive maneuver to prevent a crash. 

Table 9. Percentage of SCE Triggers That Were Valid 

Trigger Type Total Triggers Total Valid Percent Valid

Longitudinal Acceleration 257 167 65% 

Highway Deceleration 5,160 235 5% 

Swerve 71 0 0% 

Lateral Acceleration 227 4 2% 

TTC 28 18* 64% 

Yaw 11 1 9% 

User Identified 6 

Total 5,754 413 7% 

*All valid TTCs were coupled with a valid longitudinal acceleration or highway acceleration trigger. 

The experienced reductionist then assigned a severity level to each SCE. The classification of the 

413 SCEs is shown in Table 10. The operational definitions for crashes, near-crashes, and crashrelevant conflicts were the same as those used in previous NDSs (Blanco et al., in press; Dingus 

et al., 2006; Fitch et al., 2012; Hanowski et al., 2005; Simons-Morton et al., 2011). The 

examination of intersection violations was novel to this study. 

Table 10. SCE Severity Classification 

Severity n Operational Definition 

Crash 4 Any contact with an object, either moving or fixed, at any speed in which kinetic 

energy is measurably transferred or dissipated, and includes other vehicles, 

roadside barriers, objects on or off of the roadway, pedestrians, pedalcyclists, or 

animals. All severe and minor crashes are included in this category. 

Curb Strikes 2 Any crash that results from the subject vehicle (SV) making contact (intentional or 

unintentional) with a curb. 

Near-Crash 72 Any circumstance requiring a rapid, evasive maneuver by the SV, or any other 

vehicle, pedestrian, pedalcyclist, or animal to avoid a crash. A rapid, evasive 

maneuver is defined as a steering, braking, accelerating, or any combination of 

control inputs that approaches the limits of the vehicle capabilities. As a guide: SV 

braking >0.5 g or steering input that results in a lateral acceleration >0.4 g to avoid 

a crash constitutes a rapid maneuver. 
 Chapter 3: Methods 

Final Report 

18 

Severity n Operational Definition 

Crash-Relevant 

Conflict 

264 Any circumstance requiring a crash avoidance response on the part of the SV, any 

other vehicle, pedestrian, pedalcyclist, or animal that is less severe than a rapid 

evasive maneuver, but greater in severity than a “normal maneuver” to avoid a 

crash. The crash avoidance response can include braking, steering, accelerating, or 

any combination of control inputs. A crash avoidance response for the SV is 

defined as a control input that falls outside of the 99 percent confidence limit for 

control input as measured for the same subject. 

Intersection Violation 71 Any stop at a controlled intersection where the SV either (1) stops past the stop bar 

and/or in the path of cross traffic, (2) performs a rolling stop at a stop sign or righton-red with a minimum speed >=15mph regardless of relation to stop bar, or (3) 

passes through a red light in a straight crossing or left turn path. 

The experienced reductionist then identified various parameters pertaining to the conflict 

scenario. The SCEs were then passed to the reduction team, who recorded the driver’s eye glance 

locations in the 5 s prior to the onset of the SCE and 1 s afterwards. This time interval was 

selected to ensure that any driver behaviors recorded were proximal to the observed outcome and 

in order to match previous NDS methods. The reductionists also assessed the driver, vehicle, and 

environmental factors by answering the questions presented in Appendix A7. In particular, 

reductionists recorded whether specific cell phone subtasks took place in this 6-second interval. 

This reduction allowed the identification of those SCEs that occurred seconds after specific cell 

phone subtasks. The characteristics of the SCEs can be found in Appendix A8. The average SCE 

rate per 100 driving hours over all drivers was 5.97. The SCE rate per driver was computed 

across gender and two age groups (18 to 30 and 31 or older). The average SCE rate for females 

18 to 30, males 18 to 30, females 31 or older, and males 31 or older was 6.16, 8.64, 5.71, and 

5.53, respectively. The SCE rate per driver is displayed by gender and age group in Figure 8 in 

Appendix A8. 

To support a case-control investigation of the SCE risk associated with cell phone use, baseline 

samples were randomly selected from the data set and reduced. The samples were 6 seconds long 

and were selected based on each driver’s driving time in the study, which was calculated as 

follows. First, the total number of hours driven in the data set was computed. The number of 

baseline periods sampled from each driver was then based on each driver’s percentage of the 

total driving time. The study’s timeline facilitated the selection and reduction of 2,000 baseline 

periods. However, because the cell phone records indicated that approximately 10 percent would 

involve cell phone use, an additional 200 were included. Only the time the vehicle traveled 

above 8 km/h (specifically, 5 miles per hour) was considered (i.e., all SCE-baseline periods had a 

minimum speed of 8 km/h). As an example, if Driver 1’s driving time comprised 10 percent of 

the total driving time, then 220 baseline periods (10% of 2,200) would be randomly selected 

from Driver 1’s trips. A total of 2,308 baseline periods were reduced due to rounding up of the 

preset number of baseline periods to be reduced. This method was the same as that used in the 

investigation of driver distraction in commercial vehicle operations (Olson et al., 2009). An 8 

km/h threshold was used to parallel previous light-vehicle NDSs (Klauer et al., 2006; Klauer, 

Guo, Sudweeks, & Dingus, 2010); it reflects the limit at which it becomes difficult to be certain 

the vehicle is in motion. Reductionists then identified the driver, vehicle, and environmental 

factors pertaining to each SCE-baseline by answering the questions in Appendix A9. 

Reductionists also recorded the driver’s eye glance locations over a 6-second interval. 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

19 

4 Investigation of Drivers’ Cell Phone Use 

The call and text records and sampled cell phone interactions (comprising sampled calls and text 

messages) were analyzed to investigate how drivers use their cell phones while driving. The key 

objective of this analysis was to determine how cell phone use behavior changes across cell 

phone types. The behaviors analyzed included: the frequency and duration of cell phone 

subtasks, the frequency and duration of non-cell-phone-related secondary tasks performed during 

phone use, the prevalence of removing both hands from wheel during phone use, drivers’ 

emotional demeanor during cell phone interaction, where the cell phone was held during use, and 

cell phone use behavior in low and high driving task demand environments. 

Sampled cell phone calls were classified as HH, PHF, or IHF if the talking/listening subtask was 

conducted using that cell phone type. Sampled text messages were classified separately as 

Text/Browse since the subtasks reduced pertained only to the text message, not the entire call 

(this was decided after attempts to reduce the entire call would not allow the reduction to be 

completed on schedule). A sampled phone call with multiple phone types used for the 

talking/listening subtask was considered “Mixed” and was not used in the analyses. Table 11 

shows how the number of sampled phone calls and text messages were distributed across the cell 

phone classification. 

Table 11. Frequency and Percentage of Sampled Cell Phone Interactions by Cell Phone 

Type 

Cell Phone Type N Percent 

Hand-Held 795 38% 

Portable Hands-Free 218 10% 

Integrated Hands-Free 344 16% 

Text Message 648 31% 

Mixed Use 103 5% 

Total 2,108 100% 

Many of the following analyses were conducted at two speed levels: driving at speeds at or 

above 8 km/h and driving at speeds below 8 km/h. The speed levels were abbreviated to “Above 

8 km/h” and “Below 8 km/h.” If a subtask was conducted in entirety above 8 km/h, then the 

subtask was considered “Above 8 km/h.” If driving speeds fell below 8 km/h at any point during 

a subtask, the subtask was considered “Below 8 km/h.” The driving speed during a subtask was 

found by overlaying the speed data with the subtask beginning and end frames. Of the 8,240 

hours of driving, drivers were traveling above 8 km/h for 6,494 hours or 78.8 percent of total 

driving hours. Drivers traveled below 8 km/h for 1,746 hours or 21.2 percent of total driving 

hours. 

4.1 Calls Analyzed According to the Cell Phone Records 

By overlaying the cell phone records with the driving data, 14,754 calls and 8,610 text messages 

during driving were identified. The 14,754 calls consisted of 3,395 incoming calls, 10,064 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

outbound calls, 5 toll-free calls, and 1,290 calls of unknown direction. Of the 8,610 text 

messages during driving, 4,258 were received text messages, 3,994 were sent text messages, and 

358 were of unknown direction. A total of 191 drivers (94%) provided call records; however, 4 

drivers did not make calls while driving. Removing these drivers left 187 drivers (92%) in the 

call sample. Of the 121 drivers (59%) who provided text records, 12 did not have text messages 

that overlapped with driving. Removing these drivers left 109 drivers (53%) in the text sample. 

Note: a debriefing was not held to determine why some of the drivers did not make any calls 

while operating a vehicle in the study. Previous experience with NDSs would suggest that 

drivers did not adjust their calling behavior when being recorded. 

Phone calls accounted for 871 hours of the 8,240 hours of driving (10.6% of driving time). When 

driving at speeds above 8 km/h, drivers were on the phone 10.4 percent of the time and received 

or sent 0.9 text messages per hour. At speeds below 8 km/h, drivers were on the phone 13.0 

percent of the time and received or sent 1.5 text messages per hour. Drivers made an average of 

77.26 phone calls during their participation (M = 31 days) and the average phone call while 

driving was 4.02 minutes long. The distribution of number of calls per driver is displayed in 

Figure 2. The average call rate per driver was 2.00 calls per driving hour. The minimum and 

maximum call rates per driver were 0.28 calls per driving hour and 7.06 calls per driving hour, 

respectively. The distribution of the call rate (calls while driving per driving hour) per driver is 

displayed in Figure 3. 

Figure 2. Number of Calls During Driving per Driver 

Final Report 

20 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Figure 3. Number of Calls Made per Hour of Driving Above 8 km/h 

4.2 Calls Analyzed According to the Cell Phone Reduction 

As described in the methods chapter, video inspection was required to verify the type of cell 

phone used by the driver when a call was made. This section presents the results of analyses that 

were performed using the sampled cell phone interactions. 

4.2.1 Distribution of Calls Across Groups Assigned During 

Recruitment 

Drivers in the study were assigned to one of three cell phone groups (HH, PHF, or IHF) if they 

reported using that cell phone type at least 50 percent of the time. However, sampled calls were 

classified as HH, PHF, or IHF if the talking/listening subtask was conducted using that cell 

phone type, without considering the driver’s group assigned during recruitment. The number of 

sampled calls for each cell phone type was calculated for all three groups. These frequency 

counts, and the corresponding percentage of all calls made by drivers in the group, are listed in 

Table 12. Drivers in the HH group used an HH phone for 93.6 percent of calls. Drivers in the 

IHF group used an IHF system for 63.7 percent of calls and an HH cell phone in 29.7 percent of 

the calls. Drivers in the PHF group used a PHF cell phone for 32.2 percent of calls and an HH 

cell phone for 58.5 percent of calls. 

Final Report 

21 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

22 

Table 12. Frequency and Percentage of Call Interactions by Cell Phone Type Across 

Groups Assigned During Recruitment 

Group Assigned During 

Recruitment 

Hand-Held 

Interactions 

Portable 

Hands-Free 

Interactions 

Integrated 

Hands-Free 

Interactions 

Hand-Held Group 353 (93.6%) 19 (5.0%) 5 (1.3%) 

Portable Hands-Free 

Group 

307 (58.5%) 169 (32.2%) 49 (9.3%) 

Integrated HandsFree Group 

135 (29.7%) 30 (6.6%) 290 (63.7%) 

4.2.2 Call and Text Rate by Cell Phone Type 

Although the cell phone records and driving data were used to determine when a call was made 

while the vehicle was in operation, the data could not specify the type of cell phone used. To 

assess whether more calls were made with a given cell phone type over the others using the cell 

phone records, the following data step was taken. Using the sampled cell phone interactions, 

those drivers who were observed using a PHF system to talk/listen in any sampled call were 

classified as PHF users (even though they could have made HH calls; this was done because they 

had access to a PHF cell phone). Likewise, drivers who were observed to use an IHF system to 

talk/listen in any sampled calls were classified as IHF users. Drivers who were observed to just 

use an HH device to talk/listen in sampled calls were classified as HH users. A total of 12 drivers 

made both PHF and IHF cell phones and were excluded in the following analysis. Please note 

that this classification method was only used for the current analysis. The classification method 

described earlier that assigned a sampled cell phone interaction to a cell phone type based on the 

interface used during the conversation was utilized for the remaining analyses across cell phone 

types. 

The number of phone calls or text messages made per minute of driving was computed for each 

driver in the assigned groups. The mean call and text rates were tested across the three groups 

using an analysis of variance (ANOVA) and follow-up Tukey’s t-tests. Drivers who made PHF 

calls were found to make significantly more calls per minute of driving (M = 0.0409 calls per 

minute) than drivers that made just HH calls (M = 0.0262 calls per minute, p = .0007) and 

drivers that made IHF calls (M = 0.0296 calls per minute, p = .0215). The text rate, however, 

was not found to significantly differ. (Note: Hands-free texting was rare and was not considered 

in this study.) 

4.2.3 Duration of Cell Phone Use by Cell Phone Type 

Based on the reduction of the cell phone interactions, the average cell phone interaction, 

comprising VM subtasks and conversing, was 3.73 minutes long. At each speed level, a KruskalWallis test was conducted to compare duration of phone interaction across cell phone types 

before proceeding with any follow-up tests. The results of the overall Kruskal-Wallis test at both 

speed levels were significant (above 8 km/h: χ

2

 = 288.5, df = 3, p < .0001; below 8 km/h: χ

2

 = 

309.4, df = 3, p < .0001). Counts, average durations, and standard errors are listed in Table 13 for 

driving above 8 km/h and Table 14 for driving below 8 km/h. Descriptive statistics for the 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

23 

duration of the cell phone interactions are listed in Table 13 for driving above 8 km/h and Table 

14 for driving below 8 km/h. Table 13 and Table 14 also list the results of Kruskal-Wallis 

comparisons of two phone types at a time, indicated by the superscript letter next to each phone 

type. At speeds above and below 8 km/h, text/browse interactions were significantly shorter than 

call interactions regardless of phone type (p < .0001, for all phone types and speed levels). PHF 

and IHF interactions were significantly longer than HH interactions (above 8 km/h: p < .0001, p 

= .0453; below 8 km/h: p = .0028, p = .0084). PHF interactions were not found to be 

significantly different than IHF interactions when driving below 8 km/h. 

Table 13. Phone Interaction Descriptive Statistics With Kruskal-Wallis 

Test Results for Duration – Above 8 km/h 

Cell Phone Type N 

Mean 

Duration 

(Min) 

SE 25th

Percentile

75th

Percentile 

85th

Percentile

Hand-HeldA 527 3.4 0.2 0.9 3.4 6.1 

Portable Hands-FreeB 158 5.5 0.5 1.5 7.4 10.8 

Integrated Hands-FreeC 237 4.0 0.4 1.1 4.5 7.0 

Text/BrowseD 339 1.0 0.1 0.3 1.3 1.8 

The superscript letter for each cell phone type indicates significant differences found in the 

Kruskal-Wallis test for duration; if two entries have different superscript letters, they were 

found to be significantly different. 

Table 14. Phone Interaction Descriptive Statistics With Kruskal-Wallis Test Results For 

Duration – Below 8 km/h 

Cell Phone Type N 

Mean 

Duration

(Min) 

SE 25th

Percentile

75th

Percentile 

85th

Percentile

Hand-HeldA 260 2.5 0.2 0.8 2.7 4.7 

Portable Hands-FreeB 60 6.0 1.0 0.9 9.7 14.1 

Integrated Hands-FreeB 97 4.7 1.0 1.0 5.4 7.0 

Text/BrowseC 283 1.2 0.1 0.3 1.4 1.9 

The superscript letter for each cell phone type indicates significant differences found in the 

Kruskal-Wallis test for duration; if two entries have different superscript letters, they were 

found to be significantly different.

4.2.4 Frequency and Duration of Cell Phone Subtasks 

The list of cell phone subtasks, with frequency counts and summary statistics for the duration in 

seconds, is displayed in Table 15. The subtasks are grouped by the cell phone type used for the 

talking/listening or texting portion of the cell phone interaction and are listed in descending order 

by the average duration.
Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

24 

Table 15. Cell Phone Subtask Frequency and Duration With Summary Statistics 

Cell Phone Type Cell Phone Subtask N Mean (s) SE Max (s) Min (s) 25th Percentile (s) 50th Percentile (s) 

Per

Hand-Held HH: Talk/Listen 525 178.7 12.1 2045 0.9 35.3 68.5 Hand-Held HH: Dial 309 12.4 0.5 64.8 0.6 6.5 10.3 Hand-Held HH: Browse/Read, HH: Talk/Listen 133 4.4 0.8 68 0.3 1 1.6 Hand-Held HH: Locate/Answer 331 4.3 0.2 20.3 0.5 2.3 3.5 Hand-Held HH: End Task 461 4 0.1 21.2 0.1 1.9 3.3 Portable Hands-Free PHF: Talk/Listen 156 297.7 27 1733.5 0.8 59.8 173.6 Portable Hands-Free PHF: Locate/Put On 15 12 2.8 39.8 0.1 6.3 8.7 Portable Hands-Free HH: Dial 29 10.4 1.2 27.8 2.3 5.6 8.5 Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 35 4.1 0.8 17.4 0.5 1 2.7 Portable Hands-Free HH: Locate/Answer 43 3.6 0.5 21.1 0.1 1.7 2.7 Portable Hands-Free PHF: End Task 33 3 0.5 16.4 0.6 1.6 2.2 Portable Hands-Free PHF: Begin/Answer 13 2.9 1.1 15.3 0.4 0.9 1.2 Integrated Hands-Free IHF: Talk/Listen 237 226.8 21.6 2425.6 2.9 47.4 87.0 Integrated Hands-Free HH: Dial 67 12.9 1.3 47.4 1.5 5.5 9.5 Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 31 6.8 1 28.8 0.5 4 4.8 Integrated Hands-Free IHF: Begin/Answer 120 4.6 0.6 37.6 0.5 1.6 2.6 Integrated Hands-Free HH: Locate/Answer 72 3.9 0.4 15.3 0.1 2 2.7 Integrated Hands-Free IHF: End Task 154 2.9 0.2 10 0.1 1.3 2.3 Text/Browse HH: Text 207 34.6 2.5 302.2 0.7 11.8 23.7 Text/Browse HH: Browse/Read 286 13.7 0.9 87.4 0.7 4.7 9.4 Text/Browse HH: Locate/Answer 301 3.1 0.1 19.5 0.1 1.8 2.5 Text/Browse HH: End Task 352 2 0.1 24.2 0.1 0.9 1.4 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Figure 4 and Figure 5 show the frequencies (displayed above each bar) and duration of all cell 

phone subtasks across cell phone types when driving above 8 km/h and below 8 km/h, 

respectively. Of the 218 sampled PHF interactions, 97 (44.5%) did not have an HH subtask 

during the interaction. Of the 344 IHF interactions, 161 (46.8%) did not have an HH subtask 

during the interaction. 

Figure 4. Frequency and Duration for Cell Phone Subtasks When Driving 

Above 8 km/h 

Final Report 

25 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Figure 5. Frequency and Duration for Cell Phone Subtasks When Driving Below 8 km/h 

The following cell phone subtasks were analyzed for changes in duration across cell phone types: 

talking/listening, locate/answer or locate/put on (a PHF subtask only), dialing or begin/answer, 

browse/read while talking or listening, and end task. These subtasks were observed to occur in 

some form in each cell phone type. The data were transformed using a log transformation. The 

analysis was conducted using ANOVA and post hoc Tukey’s tests with 95-percent confidence 

intervals; results will be discussed here and shown in Appendix A10. 

The cell phone subtask talk/listen, plotted in Figure 6 with frequency counts for each bar, was 

tested for significant differences in duration across the three cell phone types. The results of the 

ANOVA at both speed levels were significant (above 8 km/h: F = 16.2, p < .0001; below 8 km/h: 

F = 8.34, p = 0.0003). Counts, average durations, and standard errors are listed in Table 16 for 

driving above 8 km/h and Table 17 for driving below 8 km/h. The significant differences in 

duration by cell phone type are indicated by the superscript letter next to each phone type. 

Talking/listening on a PHF phone or an IHF phone was significantly longer at both speed levels 

than talking/listening on an HH phone. When driving at speeds above 8 km/h, talking/listening 

on a PHF phone was significantly longer than talking/listening on an IHF phone. The CIs for the 

difference in log duration for HH versus PHF, listed for above 8 km/h and below 8 km/h, 

respectively, are (-0.8953, -0.3622) and (-0.8925, -0.0786). The CIs for the difference in log 

duration for HH versus IHF, listed for above 8 km/h and below 8 km/h, respectively, are (-

0.4980, -0.0405) and (-0.8444, -0.1683). The CIs for the difference in log duration for PHF 

versus IHF, listed for above 8 km/h and below 8 km/h, respectively, are (0.0581, 0.6608) and (-

0.4875, 0.4459). 

Final Report 

26 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

27 

Figure 6. Frequency and Duration of Talk/Listen Cell Phone Subtask Across Speed Level 

Table 16. Talk/Listen Subtask Descriptive Statistics With Tukey Test Results for Duration 

– Above 8 km/h 

Cell Phone Type N Mean Duration 

(s) SE 25thPercentile 

50th

Percentile 

75th

Percentile 

85th

Percentile 

Hand-HeldA 525 178.7 12.1 35.3 68.5 184.9 328.1 

Portable Hands-FreeB 156 297.7 27.0 59.8 173.6 387.9 609.5 

Integrated Hands-FreeC 237 226.8 21.6 47.4 87.0 241.7 410.1 

 The superscript letter for each cell phone type indicates significant differences found in the Kruskal-Wallis test for 

duration; if two entries have different superscript letters, they were found to be significantly different.

Table 17. Talk/Listen Subtask Descriptive Statistics With Tukey Test Results for Duration 

– Below 8 km/h 

Cell Phone Type N Mean Duration 

(s) SE 25thPercentile 

50th

Percentile 

75th

Percentile 

85th

Percentile 

Hand-HeldA 260 124.0 10.4 32.1 60.1 136.0 229.2 

Portable Hands-FreeB 60 302.6 56.8 38.0 99.0 432.2 683.5 

Integrated Hands-FreeB 97 221.3 32.4 49.0 100.2 258.6 394.8 

 The superscript letter for each cell phone type indicates significant differences found in the Kruskal-Wallis test for 

duration; if two entries have different superscript letters, they were found to be significantly different.

The duration of subtasks “locate/answer” and “locate/put on” were significantly longer for HH 

phone calls (above 8 km/h M = 4.3 s; below 8 km/h M = 4.7 s) than for text/browse samples 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

(above 8 km/h M = 3.1 s; below 8 km/h M = 3.2 s) at both speed levels [above 8 km/h CI of the 

log difference=(0.1698, 0.4374); below 8 km/h CI of the log difference=(0.0573, 0.4647)]. When 

driving above 8 km/h, the “locate/answer” or “locate/put on” subtask duration was significantly 

shorter for PHF phone calls (M = 3.6 s) than for HH samples (M = 4.3 s) [CI of the log 

difference = (-0.5574, -0.0128)]. 

The subtasks “dialing” and “begin/answer” were compared across cell phone types used for the 

subtask, regardless of the phone type used for talking/listening. At both speed levels, HH dialing 

was significantly longer in duration (above 8 km/h M = 12.4 s; below 8 km/h M = 15.9 s) than 

were PHF (above 8 km/h M = 2.9 s; below 8 km/h M = 0.7 s) or IHF begin/answer tasks (above 

8 km/h M = 4.8 s; below 8 km/h M = 6.8 s). This was because drivers would frequently pause 

during the dialing subtask to look back at the forward roadway. The mean subtask duration was 

also longer because some subtasks involved 10-digit dialing. The CIs for the difference in log 

duration for HH versus PHF, listed for above 8 km/h and below 8 km/h, respectively, are 

(1.2413, 2.2900) and (2.2527, 4.4884). The CIs for the difference in log duration for HH versus 

IHF, listed for above 8 km/h and below 8 km/h, respectively, are (0.9906, 1.3890) and (0.6874, 

1.3213). The CIs for the difference in log duration for PHF versus IHF, listed for above 8 km/h 

and below 8 km/h, respectively, are (-1.1166, -0.0351) and (-3.5122, -1.2202). 

The duration of the subtask browse/read while talking/listening was significantly longer for IHF 

phone calls than for HH phone calls at both speed levels [above 8 km/h: IHF M = 6.8 s, HH M =

4.4s, CI of the log difference= (0.0760, 1.2949); below 8 km/h: IHF M = 12.2s, HH M = 5.0s, CI 

of the log difference= (0.2268, 1.4486)]. When driving above 8 km/h, the subtask was 

significantly longer for IHF phone calls (M= 6.8 s) than for PHF phone calls (M= 4.1 s) [CI of 

the log difference= (0.0760, 1.2949)]. The task was not significantly longer during HH phone 

calls compared to PHF phone calls at either speed level. 

The duration of the subtask “end task” was significantly longer for HH (M = 4.0 s), PHF (M= 

3.0 s), or IHF phone calls (M = 2.9 s) than for text/browse samples (M = 2.0 s) when driving 

above 8 km/h [CI for the log difference for HH, PHF, and IHF, respectively: (0.6602, 0.9707), 

(0.1546, 0.9532), (0.2536, 0.6774)]. When driving below 8 km/h, the “end task” subtask duration 

was significantly longer for HH phone calls (M = 3.7 s) than for text/browse samples (M = 2.3 s) 

[CI for the log difference= (0.2908, 0.7091)]. The “end task” subtask duration was significantly 

longer for HH phone calls than for IHF phone calls when driving above 8 km/h [CI for the log 

difference=(0.1459, 0.5542)]. 

4.2.5 Frequency of Non-Cell-Phone Secondary Tasks 

Drivers also engaged in non-cell-phone-related secondary tasks during driving. The list of all 

secondary tasks is provided in Appendix A10. Reductionists noted up to three secondary tasks 

occurring during each cell phone subtask. The number of cell phone subtasks associated with and 

including a talk/listen subtask with a secondary task present was tallied for each cell phone type. 

The differences in proportions of the following secondary tasks were tested with Fisher’s tests 

across cell phone types: adjusting radio or heat, ventilation, and air-conditioning (HVAC); 

adjusting/monitoring other devices integral to vehicle; eating or drinking; and reading or writing. 

The distribution of the proportions of cell phone subtasks with the above secondary tasks is 

displayed in Figure 7. For this analysis, no distinction was made for different speed levels. 

Final Report 

28 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Adjusting the radio/HVAC did not occur significantly more often during HH, PHF, IHF, or 

Text/Browse subtasks (p=0.1694). Eating or drinking did occur significantly more often in IHF 

subtasks (0.58%) than in HH subtasks (0.15%) (p=0.0311); however, the difference is less than 

0.5 percent. The secondary tasks of reading or writing and adjusting/monitoring other devices 

integral to vehicle were not found to occur significantly more often among any of the cell phone 

types or text messaging/browsing samples. 

Figure 7. Percentage of Cell Phone Subtasks With Non-Cell-Phone-Related Secondary 

Task by Cell Phone Type

4.2.6 Comparison of Actual Call Duration to Cell Phone Records 

The reduced talk/listen duration was compared to the cell phone record duration for each 

sampled phone call. The cell phone records overestimated the talk/listen subtask by 0.46 minutes 

on average (SE = 0.01 minutes). The difference between the cell phone records and reduction 

duration was found to be significant using a paired t-test (t = 39.7, p < .0001). 

4.2.7 Percentage of Subtasks With Both Hands Removed From 

Steering Wheel 

For each cell phone subtask, reductionists recorded whether drivers removed one or both hands 

from the steering wheel. For each cell phone type, the number of subtasks with both hands 

removed from the steering wheel (no hands on wheel during subtask) was counted, as well as the 

number of subtasks with one or no hands removed from the steering wheel. Displayed in Table 

Final Report 

29 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

30 

18 is the percentage of subtasks with both hands removed for each cell phone type (calculated as 

the number of subtasks with both hands removed divided by the total number of subtasks for the 

cell phone type). The Fisher’s test results for cell phone type comparisons are in Appendix A10. 

Follow-up analyses for individual subtasks are also found in Appendix A10. At both speed 

levels, HH cell phone interactions had a significantly lower percentage of subtasks performed 

with both hands off the steering wheel than was the case for IHF cell phone interactions and 

text/browse interactions. PHF cell phone interactions had a significantly lower percentage of 

subtasks performed with both hands off the steering wheel than did IHF cell phone interactions, 

and text/browse interactions, when traveling below 8 km/h. 

Table 18. Percentage of Subtasks With Both Hands Removed From Steering Wheel by Cell 

Phone Type 

Cell Phone Type Percentage of Subtasks With Both 

Hands Removed (Above 8 km/h) 

Percentage of Subtasks With Both 

Hands Removed (Below 8 km/h) 

HH 1.6% 16.1% 

PHF 4.6% 22.2% 

IHF 7.1% 42.7% 

Text/Browse 7.1% 54.2% 

4.2.8 Emotional Demeanor During Calls 

During the reduction of cell phone subtasks, reductionists rated the emotion expressed by the 

driver as well as the emotional intensity. The rating scales used were adopted from the Facial 

Action Coding System (FACS) and other research on emotion (Ekman & Rosenberg, 1997; 

Hsieh, 2012; Zinck & Newen, 2008). The rating scales used are shown in Appendix A4. Using 

just the randomly chosen 6-second talking/listening samples, samples where the driver was rated 

to show any pronounced or severe emotion were classified as emotional conversation. Samples 

where the driver was rated to be neutral, or have any emotion slightly shown, were combined (to 

correct for any inconsistencies reductionists may have had when coding “slight” emotion). It was 

found that drivers were neutral during 96.2 percent of talking subtasks performed above 8 km/h, 

and 96.8 percent of talking subtasks performed below 8 km/h. The emotions displayed included 

happy (11.4%, 8.8%) and angry/frustrated/impatient (2.1%, 3.2%) during driving above 8 km/h 

and below 8 km/h, respectively. “Sad” and “Surprised” emotions were observed in less than 0.5 

percent of phone interactions. 

4.2.9 Where Phone Is Held During Subtask 

For each HH cell phone subtask, reductionists recorded where the driver held the cell phone 

during the majority of the subtask. Appendix A4 shows the locations that the reductionists were 

instructed to code. An analysis of where drivers held the cell phone was performed by examining 

the first HH subtask for each interaction. The various locations were also grouped into three 

classifications of visibility to a passing car: high, moderate, and low visibility. High visibility 

locations consisted of those above the steering wheel or driver-side window. Moderate visibility 

locations consisted of those at mid-steering wheel or at the driver-side window. Low visibility 

locations consisted of those low on the steering wheel or below the steering wheel.
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

31 

Table 19 lists the observed percentage of interactions by visibility classification and driver 

location. The most commonly observed phone use locations, during driving above and below 8 

km/h, were of moderate visibility (69.2% and 66.6% of interactions, respectively). Drivers in the 

southern Virginia location had the highest percentages of high visibility locations when driving 

below 8 km/h compared to drivers in North Carolina or Northern Virginia. Drivers in the 

Northern Virginia location had the highest percentages of low visibility locations at both driving 

speeds. 

Table 19. Where Phone Was Held During Subtask by Driver Location and Speed 

Speed 

Level 

Driver 

Location 

Low 

Visibility 

Moderate 

Visibility 

High 

Visibility 

Not in handOther 

Above 8 

km/h 

North 

Carolina 4.2% 75.0% 20.8% 0.0% 

Above 8 

km/h 

Northern 

Virginia 6.7% 67.4% 23.9% 2.0% 

Above 8 

km/h 

Southern 

Virginia 5.8% 70.1% 22.7% 1.4% 

Above 8 

km/h Overall 6.1% 69.2% 23.1% 1.6% 

Below 8 

km/h 

North 

Carolina 9.4% 69.8% 17.0% 9.1% 

Below 8 

km/h 

Northern 

Virginia 13.2% 66.3% 16.7% 3.7% 

Below 8 

km/h 

Southern 

Virginia 12.2% 65.9% 20.2% 1.7% 

Below 8 

km/h Overall 12.6% 66.6% 18.1% 2.7% 

4.2.10 Type of Cell Phone Used 

Touch screen cell phones were observed most often during HH subtasks (60% of subtasks 

performed both above 8 km/h and below 8 km/h). All phone types observed are listed with 

counts and proportions in Table 20 below. 

Table 20. Type of Phone Used During Hand-Held Subtask 

Type of Phone 

Above 8 km/h

(N) 

Above 8 km/h 

Percentage (%) 

Below 8 km/h 

(N) 

Below 8 km/h

Percentage (%)

Touch Screen 669 61.7 404 59.1 

BlackBerry/QWERTY on Front 172 15.9 103 15.1 

Vertical Flip-Phone 111 10.2 60 8.3 

Standard Keys on Front of Phone 87 8.0 57 8.8 

Horizontal Flip-Phone/Slide Keyboard 42 3.9 49 7.2 

Unable to Determine 4 0.4 11 1.6 
 Chapter 4: Investigation of Drivers’ Cell Phone Use 

Final Report 

32 

4.2.11 Where Phone Was Kept Prior to Reaching 

Drivers who were observed to reach for their cell phone mostly kept their cell phone in the cup 

holder (36.3%) or in their seat or lap (29.0% of interactions). Other locations within arm’s reach 

of the driver included center console storage (2.2%), in cradle (1.2%), on dashboard (1.1%), or in 

the gear shift/under the emergency brake (0.6%). Observed locations that may require drivers to 

move out of position included the passenger seat (14.2%), their purse (5.6%), in the driver door 

cubby (1.2%), and pants or shirt pocket (5.9%). Very few observations were made of drivers 

reaching onto the floor, to the instrument panel, or retrieving the phone from their visor. A plot 

of all the observed locations with percentage of observations is in Appendix A10. 

4.2.12 Cell Phone Use in Low and High Driving Task Demands 

During video reduction, reductionists recorded driving and environmental conditions during each 

subtask (see Appendix A4). These factors were used to formulate low and high driving task 

demand subsets. The driving task demands were classified as low if the road was level, straight, 

dry, did not have a junction, had a LOS (level of service) A, and when it was daylight and there 

was no adverse weather. The driving task demands were considered high when the road was near 

an interchange area, intersection, and traffic density was at a LOS C or greater. These were the 

classifications used in Fitch and Hanowski (2011). Please see Appendix A4 for operational 

definitions for each level of service. 

The duration of cell phone subtasks was tested for differences between low and high driving task 

demands using Kruskal-Wallis tests. The significant results are listed in Table 21. Additional 

results are presented in Appendix A10. For all calls made on the three cell phone types, the 

duration of the talk/listen subtask during high driving task demands was not significantly 

different from its duration in low driving task demands. However, the browsing subtask in the 

sampled text messages was significantly longer in low driving task demands than in high driving 

task demands (p = 0.0303). The text messaging subtask was also significantly longer in low 

driving task demands than in high driving task demands (p = 0.0439). For HH interactions, 

ending the task was significantly longer in high driving task demands than in low driving task 

demands (p = 0.0185). In both PHF and IHF interactions, ending the task was significantly 

longer in low driving task demands than in high driving task demands (p = 0.0360, p = 0.0407). 

The difference in duration of length for HH, PHF, and IHF end task subtasks could be due to HH 

users’ reluctance to look away from the forward roadway, perhaps using short glances to 

accomplish a task (and therefore increasing the time it takes to complete the task). All other 

subtasks were not significantly different in duration between low and high driving task demands. 

Table 21. Significant Results of Chi-Square Tests on the Duration of Cell Phone Subtasks 

Across Driving Task Demands 

Subtask 

Low Task 

Demand 

Mean (s) 

Low Task 

Demand SE 

High Task 

Demand 

Mean (s) 

High Task 

Demand SE χ2 p-value 

Text/Browse: Browsing 17.3 2.2 12.3 2.2 4.69 0.0303 

HH: End Task 2.8 0.2 3.5 0.2 5.55 0.0185 

PHF: End Task 4.2 1.1 2.3 0.2 4.4 0.036 

IHF: End Task 3.1 0.3 2.4 0.2 4.19 0.0407 
 Chapter 5: Investigation of the Risk of an SCE 

5 Investigation of the Risk of an SCE Associated With 

Cell Phone Use 

Two approaches were used to investigate the SCE risk associated with cell phone use. The first is 

called the risk rate approach and leveraged the cell phone records provided by participants. It 

was used to estimate the risk of cell phone use relative to general driving. Non-cell-phone 

secondary tasks could be performed by drivers during “general driving.” The second approach 

was a case-control experimental design that was performed to compare the risk of cell phone use 

relative to “just driving” (which excludes the performance of any secondary tasks, cell-phonerelated or not). Although each risk assessment approach has its own characteristics and 

interpretation, both approaches considered the SV to be “at-risk” only when it was moving above 

8 km/h. 

5.1 Risk Rate Approach 

A key component in assessing the SCE risk associated with cell phone use is knowledge of how 

often the cell phones were used while driving. This is referred to as the exposure of drivers to 

cell phone use. The risk rate approach took full advantage of the cell phone records to determine 

cell phone use, as opposed to case-control and case-crossover approaches that estimate cell 

phone use by sampling baseline driving periods. The risk rate approach also leveraged the 

detailed data reduction of the cell phone samples to estimate subtask durations. Overall, the 

approach is a highly efficient method for estimating the SCE risk associated with talking on a 

cell phone, talking on specific types of cell phones, performing VM cell phone subtasks, and 

overall cell phone use. However, it must be noted that the SCE risk estimated from the risk rate 

approach was relative to general driving, where other non-driving secondary tasks (e.g., eating) 

could occur. The risk rate approach does not consider other non-cell-phone-use secondary tasks 

across driving with and without using a cell phone. 

5.1.1 SCE Rate 

The risk of cell phone use relative to general driving was efficiently estimated using the acquired 

cell phone records and the reduced data set of cell phone interactions. The basic formulation for 

the SCE rate

݁ݐܴܽ

ݏܧܥ#ܵ ൌ

 was as f

݄݁݊ݓ	

ollows: 

஼௘௟௟	௉௛௢௡௘	௎௦௘

ሻ݇݉/݄	8 ൐ ݁݁݀݌ݏ	݅݊݃ݒ݅ݎ݀ሺ	݊݁݋݄݌	݈݈ܿ݁	ܽ	݅݊݃ݏݑ	ݏܽݓ	ݎ݁ݒ݅ݎ݀	

ሻ݇݉/݄	8 ൐ ݁݁݀݌ݏ	݅݊݃ݒ݅ݎ݀ሺ	݅݊݃ݒ݅ݎ݀	݄݈݅݁ݓ	݁ݏݑ	݊݁݋݄݌	݈݈ܿ݁	݂݋	݊݋݅ݐܽݎݑ݀	݈ܽݐ݋ܶ

݁ݐܴܽ

ݏܧܥ#ܵ ൌ

஽௥௜௩௜௡௚

ሻ݇݉/݄	8 ൐ ݁݁݀݌ݏ	݅݊݃ݒ݅ݎ݀ሺ	݊݁݋݄݌	݈݈ܿ݁	ܽ	݅݊݃ݏݑ	ݐ݋݊	ݏܽݓ	ݎ݁ݒ݅ݎ݀	݄݁݊ݓ	

ሻ݇݉/݄	8 ൐ ݁݁݀݌ݏ	݅݊݃ݒ݅ݎ݀ሺ	݁ݏݑ	݊݁݋݄݌	݈݈ܿ݁	ݐݑ݋݄ݐ݅ݓ	݅݊݃ݒ݅ݎ݀	݂݋	݊݋݅ݐܽݎݑ݀	݈ܽݐ݋ܶ

Cell phone use was considered a risk if ܴܽݐ݁௎	௘௡௢௛௉	௟௟௘஼௦௘ ൐ ܴܽݐ݁௜௥஽௩௜௡௚

Final Report 

33 
 

Note that ܴܽݐ݁

Chapter 5: Investigation of the Risk of an SCE 

஽௥௜௩௜௡௚ refers to the SCE rate when the driver was not engaged in cell phone 

subtasks. This reference level was used when assessing the risk rate for overall cell phone use as 

well as the risk rate for subtask categories, such as conversing on a cell phone, performing callrelated VM cell phone subtasks, and text-messaging-related VM cell phone subtasks. For 

exam

ݐܴܽ

ݏܧܥ#ܵ

݁

ple, the SCE rate of call-related VM

݈݈ܿܽ	݉݁݀ݎ݋݂ݎ݁݌	ݎ݁ݒ݅ݎ݀	݄݁݊ݓ	

 subtask

݁݀ݐ݈݁ܽݎ െ

s was calcu

ൌ

஼௔௟௟ିோ௘௟௔௧௘ௗ	௏ெ

ݏ݇ݏܽݐܾݑݏ	ܯܸ	

lated as follo

݅݊݃ݒ݅ݎ݀ሺ	

ws: 

ሻ݇݉/݄	8 ൐ ݁݁݀݌ݏ	

Call-related VM subtasks were considered to be

݇݉	8 ൐ ݁݁݀݌ݏ	݅݊݃ݒ݅ݎ݀ሺ	ݏ݇ݏܽݐܾݑݏ	ܯܸ	݁݀ݐ݈݁ܽݎ െ ݈݈ܿܽ	݂݋	݊݋݅ݐܽݎݑ݀	݈ܽݐ݋ܶ

ܴܽݐ݁௟௟௔஼ିோ௘௟௔௧௘ௗ	௏ெ ൐ ܴܽݐ݁௜௥஽௩௜௡௚

 associated with an increased SCE risk if 

/݄ሻ

The risk rate approach did not investigate the risk of specific cell phone VM subtasks because 

some of the VM subtasks were infrequently observed in the obtained sample. A reliable estimate 

for the duration of these subtasks could not be generated. VM subtasks were thus aggregated into 

overall call-related VM subtasks and text-messaging-related VM subtasks when evaluating their 

SCE risk. 

5.1.2 Data Processing 

The risk rate approach required the following two parameters: 

1. The number of SCEs associated with each cell phone subtask 

2. The duration of each cell phone subtask 

The specific cell phone subtasks observed in the 6-second window surrounding each SCE were 

identified. The SCEs were then classified as either cell-phone-related or not cell-phone-related. 

The cell phone records and the reduced cell phone subtasks were used to estimate the duration of 

the subtasks. The cell phone records and the cell phone use reduction were also used to estimate 

the duration of general driving. The estimation procedures are described below. The combination 

of the cell phone records and the reduced cell phone subtasks provided an unprecedented level of 

cell phone exposure information. 

5.1.3 Estimation Procedure 

The subtask durations were estimated for the following categories: (1) cell phone use – 

collapsed, (2) call-related VM, (3) text-messaging-related VM, (4) talking/listening, (5) 

talking/listening HH, (6) talking/listening PHF, (7) talking/listening IHF, (8) HH cell phone use 

(collapsed), (9) PHF cell phone use (collapsed), and(10) IHF cell phone use (collapsed). The 

estimation procedure details are provided in Appendix A.11. 

5.1.3.1 Estimating the Duration of Cell Phone Talking 

Among all cell phone subtasks, talking was the easiest to estimate. The starting time and duration 

of cell phone talking was directly available from cell phone records. By overlaying the cell 

Final Report 

34 
 Chapter 5: Investigation of the Risk of an SCE 

phone record with the vehicle’s speed data, the total duration of talking/listening while driving 

above 8 km/h was computed. Note: the cell phone records rounded each call up to the nearest 

minute, which could overestimate the talking time. This round-up bias was assessed by 

comparing the duration of the reduced cell phone interactions to the cell phone records. The 

round-up bias was estimated by each cell phone user group and the direction of the cell phone 

calls. The duration of cell phone talking calculated from the cell phone records was then adjusted 

based on this information. 

The reduced cell phone samples revealed that many drivers used multiple types of cell phones 

(HH, PHF, or IHF) during their participation in the study, regardless of what they reported 

during study recruitment. After calculating the talking time for each driver, an estimate of how 

much of their talking time was spent on each of the three cell phones types was generated. The 

durations were then estimated using the reduced cell phone samples. For each driver, the 

proportion of their sampled talking time spent on each of the three cell phone types was 

estimated. These proportions were then multiplied by the driver’s total talking time as calculated 

from the cell phone records. 

5.1.3.2 Estimating the Total Duration of Cell Phone VM Subtasks 

The VM cell phone subtasks were not directly available from the cell phone records. VM subtask 

durations were thus estimated using the reduced cell phone samples. The average duration of 

VM subtasks per call/text was calculated by stratifying across call/text messaging direction and 

drivers’ assigned cell phone type group. These averages were then multiplied by the number of 

calls/text messages in the cell phone records to estimate the total VM time. Two VM 

subcategories were also created: (1) call-related VM subtasks, and (2) text-messaging-related 

VM subtasks. 

Call-related VM subtasks were subtasks that were VM in nature and were performed to initiate 

or end a cell phone conversation. Push to begin a PHF call and Push to begin an IHF call were 

included in this category. The call-related VM subtask duration was estimated as follows. First, 

the amount of time spent performing VM subtasks for a given HH, PHF, or IHF interaction was 

computed by subtracting the reduced talk time from the overall length of the reduced cell phone 

interaction. Because it was hypothesized that the VM subtask duration would differ based on call 

direction and the originally assigned cell phone group, the average VM subtask time per call was 

calculated by user group and call direction. This average was then multiplied by the number of 

calls to estimate the total call-related VM time. 

Subtasks observed during sampled text messages were classified as text-messaging-related VM 

subtasks (e.g., locating a cell phone, text messaging, browsing/reading, and ending cell phone 

use). The durations of these subtasks were summed for each text message. The average VM 

subtask time per text message was calculated by user group and text direction. This average was 

then multiplied by the number of text messages to estimate the total text-messaging-related VM 

time. One complication in doing so was that text records were only available for 121 of the 204 

drivers. To make maximum use of information from all drivers, the research team estimated the 

VM subtask duration for the 83 drivers with missing text records by assuming they had the same 

text usage patterns as the 121 drivers with text records. The average text messaging duration per 

Final Report 

35 
 Chapter 5: Investigation of the Risk of an SCE 

hour of driving was computed using the 121 drivers and was applied to the remaining 83 drivers 

to estimate the total duration of text messaging. 

5.1.3.3 Estimating the Duration of Overall Cell Phone Use 

The total cell phone use time was computed by summing the total estimated talking time with the 

total estimated call-related VM time and the total estimated text-messaging-related VM time. A 

similar procedure was used to compute how much time was spent using the three types of cell 

phones. The total HH cell phone use time was computed by summing the total estimated HH cell 

phone talking time with the total estimated HH cell phone call-related VM subtask time and the 

total estimated text-messaging-related VM subtask time. Note: all text messaging-related VM 

subtasks were strictly assigned to HH cell phone use. The total PHF cell phone use time was 

computed by summing the total estimated PHF cell phone talking time with the total estimated 

PHF cell phone call-related VM subtask time. The total IHF cell phone use time was computed 

by summing the total estimated IHF cell phone talking time with the total estimated IHF cell 

phone call-related VM subtask time. 

5.1.3.4 Estimating the Total General Driving Time 

The total time spent not using a cell phone – referred to as general driving – was computed by 

subtracting the total estimated cell phone use time from the total driving time. 

5.1.4 Analysis 

A mixed effect Poisson model was used to assess the SCE risk associated with cell phone 

subtasks. The model formulation is shown below: 

Yij ~ Poisson(Eijij)

where 

 Yij is the observed SCE frequency for driver i and cell phone use stratification j, as 

measured by the number of SCEs; cell phone use stratification indicator j =0 indicates 

reference level (no cell phone use) and j=1 indicates cell phone use; 

 Eij is the duration traveled by driver i above 8 km/h under cell phone use stratification j; 

 ij is the corresponding expected SCE rate, as measured by the number of SCEs per unit 

time of driving. 

A log link function connects ij with a set of covariates, 

ߙ

log( )    X β 

indicator variable for driver i 

௜ ݅

ij

௜ߙ

0 ij i

ݔ

where is a random effect term for driver and 

௜௝ ൌ ൜0

 follows a normal distribution; Xij is an 

1

݅݊݃ݒ݅ݎ݀

݀

ݐݑ݋݄ݐ݅ݓ	

݄݈݅݁ݓ	݅݊݃ݒ݅ݎ

	݈݈ܿ݁

and cell phone use st

݊݁݋݄݌	

݅݊݃ݏݑ	

݁ݏݑ	

	ܽ	݈݈ܿ݁

݁݊ܿ݁ݎ݂݁݁ݎሺ	

݊݁݋݄݌	

ratification j 

		

 ሻ݈݁ݒ݈݁	

Final Report 

36 
 Chapter 5: Investigation of the Risk of an SCE 

and β is a regression parameter. A significant β indicates a statistically significant difference in 

the SCE rate between cell phone use and non-cell-phone use while driving. 

5.1.5 Results 

Table 22 presents the risk rate ratios and 95-percent confidence limits for the cell phone 

subtasks. The risk rate ratios were investigated using crashes, near-crashes, and crash-relevant 

conflicts. The risk rates were also investigated by including intersection violations (i.e., stops 

past the stop bar). However, intersection violations were relatively noisy. Caution should thus be 

used when interpreting the results that included intersection violations. 

The risk rate approach found that talking on any kind of cell phone was not associated with an 

increased SCE risk. Cell phone VM subtasks (collapsed together) were found to be associated 

with an increased SCE risk (Risk Rate Ratio = 2.93). This was found for both call-related VM 

subtasks (Risk Rate Ratio = 3.34) and text messaging-related VM subtasks (Risk Rate Ratio = 

2.12). As such, when the risk of HH cell phone use (collapsed across VM and talking/listening 

subtasks) was computed, it was also found to be associated with an increased SCE risk (Risk 

Rate Ratio = 1.73). 

Final Report 

37 
Chapter 5: Investigation of the Risk of an SCE 

Final Report 

38 

Table 22. Risk Rate Ratios for Cell Phone Use Subtasks and Aggregate Use While Drivi

Subtask 

Rate 

Ratios 

for 

Crashes, 

NearCrashes, 

and 

CrashRelevant 

Conflicts 

Rate Ratios 

for 

Crashes, 

NearCrashes, 

CrashRelevant 

Conflicts, 

and 

Intersection 

Violations 

LCLs 

for 

Crashes, 

NearCrashes, 

and 

CrashRelevant 

Conflicts 

LCLs for 

Crashes, 

NearCrashes, 

CrashRelevant 

Conflicts, 

and 

Intersection 

Violations 

UCLs 

for 

Crashes, 

NearCrashes, 

and 

CrashRelevant 

Conflicts 

UCLs 

for Crashes, 

NearCrashes, 

CrashRelevant 

Conflicts, 

and 

Intersection 

Violations 

p-v

f

Cra

N

Cra

a

Cr

Rel

Con

Cell Phone Use – Collapsed 1.32 1.29 0.96 0.96 1.81 1.72 Visual-Manual 2.93* 2.60* 1.90 1.72 4.51 3.92 <  Call-Related Visual-Manual 3.34* 3.23* 1.76 1.80 6.35 5.79  Text-Related Visual-Manual 2.12* 1.76 1.14 0.95 3.96 3.27 Talking/Listening 0.84 0.90 0.55 0.62 1.29 1.31  Talking/Listening HH 0.84 1.03 0.47 0.63 1.53 1.68  Talking/Listening PHF 1.19 0.98 0.55 0.46 2.57 2.12  Talking/Listening IHF 0.61 0.62 0.27 0.29 1.41 1.35 HH Cell Phone Use (Collapsed) 1.73* 1.71* 1.20 1.23 2.49 2.38 PHF Cell Phone Use (Collapsed) 1.06 0.88 0.49 0.41 2.30 1.89 IHF Cell Phone Use (Collapsed) 0.57 0.58 0.25 0.27 1.31 1.26 

* Indicates significant effect at the .05 level of significance. 
 Chapter 5: Investigation of the Risk of an SCE 

Final Report 

39 

5.2 Case-Control Approach 

To estimate the risk of cell phone subtasks relative to “just driving,” where all non-driving 

secondary tasks are excluded, a case-control experimental design was used. Drivers’ exposure to 

cell phone use was estimated based on how often cell phone subtasks were observed in the 2,308 

baseline samples. Because reductionists identified what secondary tasks took place in the 6-

second baseline and SCE samples, samples where “just driving” was observed could be selected. 

However, it should be noted that many samples were excluded in doing so; only 46 percent of 

the samples constituted “just driving.” 

5.2.1 Equations 

ORs were calculated to estimate the SCE risk associated with cell phone subtasks relative to 

“just driving.” The setup of the 2x2 contingency table and the OR formula are shown below 

(Table 23). 

Table 23. 2x2 Contingency Table for Cell Phone Use and SCE Outcome 

Just Driving Cell Phone Subtask 

Baseline n11 n12 n1. 

SCE n21 n22 n2. 

 n.1 n.2 n.. 

Odds Ratio = (n11)(n22)/(n21)(n12) 

As an example, the OR for investigating the association between talking on a cell phone and 

being involved in an SCE was computed as follows (the data used are shown in Table 24): 

Table 24. Contingency Table for Talking on a Cell Phone and SCE Outcome 

Just Driving HH: Talk/Listen 

Baseline 1,068 (A) 259 (B) 1,327

SCE 154 (C) 28 (D) 182

 1,222 287 1,509

ܱܴ ൌ 	 ஺ൈ஽

஻ൈ஼ ܱܴ ൌ 	 ଵ,଴଺଼	ൈ	ଶ଼ଶହଽ	ൈଵହସ ܱܴ ൌ 	0.7497

The 95-percent confidence interval for talking on a cell phone was calculated to determine if the 

OR of 0.75 was significant. The formulas to calculate the 95th percentile lower confidence limit 

(LCL) and upper confidence limit (UCL) are shown below: 

ܷܮܥ ൌ ܱܴ	 ൈ ݁ଵ.ଽ଺ൈටభ

ೌାభ್ାభ೎

ାభ

೏ ܷܮܥ ൌ 0.7497	 ൈ ݁1.96ൈට 1

1068൅ 1259൅ 1154൅ 128

 1.1467 ൌ ܮܥܷ
 Chapter 5: Investigation of the Risk of an SCE 

Final Report 

40 

ܮܥܮ ൌ ܱܴ	ൈ݁

ିଵ.ଽ଺ൈටభ

ೌାభ್ାభ೎

ାభ

೏ ܮܥܮ ൌ 0.7497	 ൈ ݁ିଵ.ଽ଺ൈට భభబలఴା భమఱవା భభఱరା భమఴ

 0.4902 ൌ ܮܥܮ

Since the 95-percent confidence interval included “1.0,” there is no evidence that just talking on 

a cell phone is associated with an increased SCE risk. 

5.2.2 Results 

The SCE risk of cell phone subtasks relative to “just driving” is shown in Table 25. The SCEs 

used to compute the ORs excluded intersection violations since analyses that included them 

found fewer significant effects, suggesting that the violations added noise to the data without a 

commensurate increase in the predictive ability of the statistical model. It can be seen that the 

case-control approach found VM subtasks to be associated with an increased SCE risk (OR = 

1.73), while talking on a cell phone, regardless of type of interface, was not found to be 

associated with an increased SCE risk. In further isolating the VM subtasks, locating/answering 

an HH cell phone was found to be associated with an increased SCE risk (OR = 3.65). This may 

be related to the inherent urgency in answering a call before it transfers to voice mail. 

Table 25. Odds Ratios for Cell Phone Use Subtasks and Aggregate Use While Driving 

Subtask OR LCL UCL #SCE #BL SCE 

Total BL Total Total 

Cell Phone Use 

(Collapsed) 1.10 0.80 1.53 57 358 211 1426 1637 

Visual-Manual Subtasks 1.73* 1.12 2.69 29 116 183 1184 1367 

 Text 

Messaging/Browsing 1.73 0.98 3.08 16 64 170 1132 1302 

 Locate/Answer 3.65* 1.67 8 10 19 164 1087 1251 

 Dial 0.99 0.12 8.11 1 7 155 1075 1230 

 Push to Begin/End Use 0.63 0.08 4.92 1 11 155 1079 1234 

 End HH Phone Use 1.26 0.43 3.71 4 22 158 1090 1248 

Talking on Cell Phone 0.75 0.49 1.15 28 259 182 1327 1509 

 HH Talking 0.79 0.43 1.44 13 114 167 1182 1349 

 PHF Talking 0.73 0.36 1.47 9 86 163 1154 1317 

 IHF Talking 0.71 0.30 1.66 6 59 160 1127 1287 

HH Cell Phone Use 

(Collapsed) 1.39 0.96 2.03 41 204 195 1272 1467 

PHF Cell Phone Use 

(Collapsed) 0.79 0.40 1.55 10 88 164 1156 1320 

IHF Cell Phone Use 

(Collapsed) 0.62 0.26 1.46 6 67 160 1135 1295 

* Indicates significant effect at the .05 level of significance. 
 Chapter 6: Investigation of Driver Performance 

Final Report 

41 

6 Investigation of Driver Performance When Using a 

Cell Phone 

The effects of using a cell phone on driver performance were investigated by comparing driver 

performance on multiple dimensions when executing specific cell phone subtasks to their 

performance 30 s prior to executing the first subtask in the interaction. Measures were taken to 

investigate whether drivers’ vehicle control degraded due to distraction (Table 26), as well as 

whether drivers purposefully changed their driving style to compensate for the increased 

workload (Table 27). Finally, measures were taken to investigate whether executing the subtasks 

had an effect on downstream traffic (Table 28). 

Table 26. Driver Performance Degradation Measures 

Measure Operational Definition Subtask Interval 

SubtaskBaseline 

Interval 

Percentage of Total 

Eyes Off Road Time 

(TEORT) 

A measure of visual behavior to the forward 

roadway. Computed as the number of frames 

the driver’s eyes were off the forward roadway 

divided by the total number of frames in the 

sample interval. EORT included glances to the 

mirrors and side windows. 

Interval spanned the 

duration of the subtask. 

However, only one 

randomly selected 6-s 

interval was selected for 

talking, as well as holding, 

because these subtasks 

could take minutes to 

perform. These intervals are 

referred to as sample 

intervals in this column. 

Sample interval 

spanned 20 s 

starting 30 s back 

from the first cell 

phone interaction. 

This interval is 

referred to as 

sample interval in 

this column. 

Speed Standard 

Deviation 

A measure of vehicle longitudinal control. It 

consists of the SV’s speed standard deviation 

computed over the sample interval. 

20 s beginning from start of 

the subtask. For example, if 

reaching for a cell phone 

took 4 s, then speed 

standard deviation was 

measured over 20 s 

beginning at the start of the 

reaching subtask. Note: this 

interval could overlap with 

subsequent subtasks, like 

dialing. 

20-s baseline 

sample. 

Headway Standard 

Deviation 

A measure of vehicle longitudinal control. 

Computed as the standard deviation of the 

SV’s headway to a lead vehicle over the 

sample interval. Reductionists visually 

verified the lead vehicle’s radar target ID. 

These data were used when computing the 

headway standard deviation. 

20 s beginning from start of 

sample. 

20-s baseline 

sample. 
 Chapter 6: Investigation of Driver Performance 

Final Report 

42 

Measure Operational Definition Subtask Interval 

SubtaskBaseline 

Interval 

Unintentional Lane 

Bust Rate 

A measure of vehicle lateral control. 

Reductionists used a lane tracker tool to 

identify unintentional lane busts that occurred 

over the sampled interval. This count was then 

divided by the sample duration to compute the 

unintentional lane bust rate. 

Subtask interval. 20-s baseline 

interval. 

Delayed Reaction to an 

External Event 

A qualitative measure of long reaction time. 

Reductionists assessed whether the driver had 

a delayed reaction to an unexpected external 

event within 6 s of the start of the sample. An 

unexpected external event was anything 

unexpected or out of the ordinary that 

presented a safety hazard (e.g., vehicle, 

pedestrian, or animal unexpectedly entering 

roadway. This could also have included a 

delayed reaction to a red light). Driver 

reaction was assessed as either: (1) fully 

prepared, driver reacts in a timely manner, (2) 

somewhat caught off guard, (3) very much 

caught off guard, and (4) extremely caught off 

guard. 

6 s beginning from start of 

the subtask. 

First 6 s of the 

baseline sample. 

Peak Deceleration A measure of vehicle longitudinal control. 

Refers to the peak deceleration of the SV over 

a 10-second interval. 

10 s beginning from start of 

the subtask. 

First 10 s of the 

baseline sample. 

If Driver Crosses an 

Intersection, Does 

Driver Scan (Providing 

He/She Should) 

If the driver crossed an intersection within 10 

s from the start of the sample, reductions 

indicated whether the driver scanned the 

intersection prior to entering it. If the vehicle 

crossed a four-way intersection, the driver was 

considered to have scanned if he looked left 

and right. The sequence of locations was not 

considered. If the driver crossed a right 

junction, then he was considered to have 

scanned if he looked right. The same was true 

when crossing left junctions. 

10 s beginning from start of 

the subtask. 

First 10 s of the 

baseline sample. 

If Driver Crosses an 

Intersection, Does 

Driver Violate the 

Intersection 

If the driver had to stop at an intersection 

encountered within 10 s of the sample, 

reductions marked a violation if the driver 

stopped past the stop bar, had a rolling stop 

less than 15 mph, or had a rolling stop greater 

than 15 mph. 

10 s beginning from start of 

the subtask. 

First 10 s of the 

baseline sample. 

If the SV Changes 

Lanes, Does Driver Use 

the Turn Signal 

If the driver started, or was in the process of, 

changing lanes within a 10-second interval 

spanning 5 s before the start of the sample up 

to 5 s after the start of the sample, then a 

measure of whether the turn signal was 

activated in this interval was taken from the 

vehicle network. 

10 s (± 5s centered on the 

start of the subtask) 

10 s (± 5s centered 

on start of baseline 

sample) 

*Note: the sample intervals were chosen such that, if needed, they could be combined with the SCE-baseline periods 

in future analyses. This was not done in the current study, however. 
 Chapter 6: Investigation of Driver Performance 

Final Report 

43 

Table 27. Driver Adaptation Measures 

Measure Operational Definition Subtask Interval 

SubtaskBaseline 

Interval 

Speed Refers to the vehicle speed at the start of the 

sample interval. 

Recorded at the first frame 

of the subtask. 

Recorded at first 

frame of the 

baseline sample. 

Headway Refers to the SV’s headway to a lead vehicle 

at the start of the sample interval. 

Reductionists visually verified the lead 

vehicle’s radar target ID prior to computing 

the headway. 

Recorded at the first frame 

of the subtask. 

Recorded at first 

frame of the 

baseline sample. 

Time-to-Collision 

(TTC) 

Refers to the SV TTC to a lead vehicle at the 

start of the sample interval. TTC was 

computed as the range to the lead vehicle 

divided by the range rate to the lead vehicle. 

Reductionists visually verified the lead 

vehicle’s radar target ID prior to computing 

the TTC. 

Recorded at the first frame 

of the subtask. 

Recorded at first 

frame of the 

baseline sample. 

Lane Change Reductionists indicated whether the driver 

started, or was in the process of, changing 

lanes within a 10-second interval spanning 5 s 

before the start of the sample up to 5 s after 

the start of the sample. The lane change could 

be in any direction. 

10 s (± 5s centered on the 

start of the subtask) 

10 s (± 5s centered 

on start of baseline 

sample) 

Lane Position Reductionists indicated the lane position of the 

SV at the start of the sample interval. A score 

of “1” was assigned to the leftmost lane. 

Reductionists also indicated the number of 

lanes available for travel so that the rightmost 

lane could be identified. 

Recorded at the first frame 

of the subtask. 

Recorded at first 

frame of the 

baseline sample. 

Table 28. Measures of Effects on Downstream Traffic 

Measure Operational Definition Subtask Interval 

SubtaskBaseline 

Interval 

Range to Rear Vehicle 

(RV) 

A measure of whether the RV was tailgating 

the SV. Subject’s vehicles were not equipped 

with a rear facing radar unit. However, 

reductionists rated the range to the RV using 

the video image of the rearward roadway. 

Appendix A4 describes how these ratings 

were made. 

Recorded at the first frame 

of the subtask. 

Recorded at first 

frame of the 

baseline sample. 

Lane Change A measure of whether the RV passed the SV. 

Reductionists indicated whether the RV 

started, or was in the process of, changing 

lanes within 10 s of the start of the sample. 

The lane change could be in any direction. 

10 s beginning from start of 

subtask. 

10 s beginning 

from start of 

baseline sample. 
 Chapter 6: Investigation of Driver Performance 

6.1 Performance Degradation When Using a Cell Phone 

The performance measures analyzed were selected to investigate drivers’ visual behavior, 

longitudinal vehicle control, lateral vehicle control, and degraded reaction time to unexpected 

events when using a cell phone. All inferential tests were conducted at the .05 level of 

significance. 

6.1.1 Percent Total-Eyes-Off-Road Time 

The mean percent TEORT when drivers performed various cell phone subtasks above 8 km/h 

was investigated. Percent TEORT was computed as the total number of samples where the 

driver’s eyes were off the forward roadway divided by the total number of samples in the subtask 

or baseline sample. Percent TEORT is a normalized measure that allows the comparison of 

driver visual behavior across subtasks of varying durations. To perform a controlled comparison 

of percent TEORT, inferential statistics were only performed when eye glance data were 

available for both the subtask and its matched baseline sample. For each subtask, a one-way 

within-subject ANOVA was performed to investigate whether the mean percent TEORT when 

performing the subtask differed from the mean percent TEORT during its matched baseline 

sample. Similar to cell phone use analyses, only interactions that were categorized as one of the 

three cell phone types, or were a sampled text message, were analyzed. Table 29 presents the 

ANOVA summary results. 

 

Final Report 

44 
 Chapter 6: Investigation of Driver Performance 

Table 29. ANOVA Results for Within-Subject Comparisons of Mean Percent TEORT 

Between Each Subtask and Its Matched Baseline 

Cell Phone 

Type Subtask 

Baseline 

Mean 

(%) 

SE 

(%) 

Subtask 

Mean 

(%) 

SE 

(%) n df1 df2 F Stat p-value

HH HH: Locate/Answer 15.2 1.0 33.1 1.6 201 1 87 105.18 < .0001

HH HH: Dial 16.1 1.4 59.5 1.4 131 1 64 498.36 < .0001

HH HH: Talk/Listen 14.6 0.9 9.5 0.9 207 1 91 14.80 .0002 

HH HH: Browse/Read, 

HH: Talk/Listen 12.3 1.7 71.5 2.7 56 1 34 357.38 < .0001

HH HH: End Task 14.8 1.0 44.1 2.0 179 1 84 120.07 < .0001

PHF PHF: Locate/Put On 14.6 8.8 25.5 3.8 4 - - - - 

PHF PHF: Begin/Answer 13.6 1.8 24.1 12.1 8 1 5 0.90 .3852 

PHF HH: Locate/Answer 16.7 3.1 46.3 5.9 23 1 12 19.71 .0008 

PHF HH: Dial 19.3 3.4 63.3 3.2 13 1 7 50.11 .0002 

PHF PHF: Talk/Listen 16.4 1.9 16.0 2.1 49 1 22 0.02 .8776 

PHF PHF: End Task 13.0 5.3 21.6 9.1 9 1 6 0.44 .5316 

PHF HH: Browse/Read, 

PHF: Talk/Listen 15.9 3.3 72.8 6.3 15 1 11 117.34 < .0001

IHF IHF: Begin/Answer 11.7 1.2 52.7 2.9 69 1 36 117.58 < .0001

IHF HH: Locate/Answer 15.0 2.2 43.4 4.3 39 1 25 32.13 < .0001

IHF HH: Dial 15.9 2.6 64.5 2.7 31 1 21 189.12 < .0001

IHF IHF: Talk/Listen 12.4 1.0 15.6 1.7 108 1 49 1.32 .2560 

IHF IHF: End Task 11.7 1.1 45.4 3.4 74 1 42 64.62 < .0001

IHF HH: Browse/Read, 

IHF: Talk/Listen 14.6 2.6 58.1 5.3 14 1 11 56.51 < .0001

Text/Browse HH: Locate/Answer 15.5 0.9 33.2 1.6 192 1 55 28.42 < .0001

Text/Browse HH: Browse/Read 16.0 1.0 62.9 1.3 157 1 47 294.37 < .0001

Text/Browse HH: Text 16.1 1.3 67.6 1.2 112 1 26 263.32 < .0001

Final Report 

45 

Text/Browse HH: End Task 15.8 0.9 29.6 1.9 178 1 49 19.69 < .0001

With respect to HH cell phone use, locating the cell phone, dialing, browsing, text messaging, 

simultaneously browsing and conversing, and ending cell phone use were all found to 

significantly increase the percentage of time drivers took their eyes off the forward roadway. 

Drivers’ mean percent TEORT during baseline samples ranged from 12.3 to 16.1 percent, while 

their mean TEORT during these cell phone subtasks ranged from 33.1 to 71.5 percent. 

Conversing on an HH cell phone, however, was found to significantly lower drivers’ mean 

percent TEORT from 14.6 to 9.5 percent. 
 Chapter 6: Investigation of Driver Performance 

With respect to PHF cell phone use, locating the HH cell phone, dialing on an HH cell phone, 

and simultaneously browsing and conversing on the PHF cell phone were all found to 

significantly increase the percentage of time drivers took their eyes off the forward roadway. 

Drivers’ mean percent TEORT during baseline samples ranged from 15.9 to 19.3 percent, while 

their mean percent TEORT during these subtasks ranged from 46.2.4 to 72.8 percent. Conversing 

on a PHF cell phone did not have a significant effect on mean percent TEORT. The same was 

true for pressing a button to begin/answer a PHF call and pressing a button to end a PHF call; 

however, this was most likely because of a small sample size (n = 8 for pressing a button to 

begin/answer a PHF call and n = 9 for pressing a button to end a PHF call). Note, there was an 

insufficient amount of data to test for differences in TEORT when locating a PHF device (n = 4). 

The paucity of matched samples could be because these subtasks and/or baseline periods 

occurred when the vehicle was stopped or because drivers initiated or ended the call before or 

after their trip. 

With respect to IHF cell phone use, locating the HH cell phone, pressing a button to 

begin/answer an IHF call, dialing on an HH cell phone, simultaneously browsing and conversing 

on the IHF cell phone, and pressing a button to end an IHF call were all found to significantly 

increase the percentage of time drivers took their eyes off the forward roadway. Drivers’ mean 

percent TEORT during baseline samples ranged from 11.7 to 15.9 percent, while their mean 

percent TEORT during these cell phone subtasks ranged from 43.4 to 64.5 percent. Conversing 

on an IHF cell phone did not have a significant effect on mean percent TEORT. 

An objective of this study was to assess whether certain types of cell phones resulted in a greater 

amount of visual distraction than others. To answer this research question, changes in mean 

percent TEORT when performing a subtask were compared across cell phone types. Percent 

TEORT difference scores were created by subtracting the matched baseline percent TEORT 

from the subtask percent TEORT. Functionally similar subtasks were then compared across cell 

phone types using a one-way between-subjects ANOVA. Table 30 presents the mean percent 

TEORT differences for the subtasks and their respective test statistics. 

 

Final Report 

46 
 Chapter 6: Investigation of Driver Performance 

Table 30. Mean Percent TEORT Difference Scores for Various Subtasks Across Cell Phone 

Types 

Action Subtask Mean 

Difference SE n df1 df2 F Statistic p-value 

Locate Device HH: Locate/Answer 17.9 1.7 201 2 127 1.03 .3611 

Locate Device HH: Locate/Answer for PHF 26.8 5.9 27 2 127 1.03 .3611 

Locate Device HH: Locate/Answer for IHF 28.4 4.4 39 2 127 1.03 .3611 

Initiate Call HH: Dial 43.4 1.8 131 4 133 4.07 .0038 

Initiate Call HH: Dial for PHF 44.0 4.7 13 4 133 4.07 .0038 

Initiate Call HH: Dial for IHF 48.6 3.1 31 4 133 4.07 .0038 

Initiate Call PHF: Begin/Answer 10.6 12.1 8 4 133 4.07 .0038 

Initiate Call IHF: Begin/Answer 41.0 3.0 69 4 133 4.07 .0038 

Talk/Listen HH: Talk/Listen -5.1 1.2 207 2 162 4.77 .0097 

Talk/Listen PHF: Talk/Listen -0.4 2.5 49 2 162 4.77 .0097 

Talk/Listen IHF: Talk/Listen 3.2 1.8 108 2 162 4.77 .0097 

Browse While 

Conversing 

HH: Browse/Read, HH: 

Talk/Listen 59.2 2.8 56 2 56 3.77 .0292 

Browse While 

Conversing 

HH: Browse/Read, PHF: 

Talk/Listen 56.2 6.4 15 2 56 3.77 .0292 

Browse While 

Conversing 

HH: Browse/Read, IHF: 

Talk/Listen 43.5 5.1 14 2 56 3.77 .0292 

End Use HH: End Task 29.3 2.0 179 2 132 3.05 .0507 

End Use PHF: End Task 8.6 7.8 9 2 132 3.05 .0507 

End Use IHF: End Task 33.6 3.5 74 2 132 3.05 .0507 

The method used to initiate a call was found to significantly affect the mean change in percent 

TEORT, F(4,133) = 4.07, p = .0038. A Tukey-Kramer test revealed that pressing a button to 

begin/answer a PHF call yielded an increase in mean percent TEORT (10.6%) that was 

significantly less than the increases in mean percent TEORT from dialing an HH cell phone 

(43.4% when making HH calls, 44.0% when making PHF calls, and 48.6% when making IHF 

calls), and pressing a button to begin/answer an IHF call (41.0%). Reasons why this was found 

could be that: (1) drivers looked at the HH cell phone when dialing, (2) pressing a button to 

begin an IHF call included cases when the driver dialed using the integrated keyboard, and (3) 

Final Report 

47 

some drivers were observed to interact with the vehicle’s center stack when beginning/answering 

an IHF call (e.g., to lower the HVAC fan, or increase the volume), and (4) drivers could continue 

to look forward when pressing a button on their headset or earpiece to begin/answer a PHF call. 

Note, drivers using PHF headsets or earpieces may not need to lower the HVAC fan or music 

volume when beginning a call because of the proximity of the microphone and earpiece to the 

driver. 
 Chapter 6: Investigation of Driver Performance 

Final Report 

48 

The method used to converse was found to significantly affect the change in mean percent 

TEORT, F(2,162) = 4.77, p = .0097. A Tukey-Kramer test revealed that conversing on an HH 

cell phone yielded a decrease in mean percent TEORT (5.1%) that was significantly different 

than the change in mean percent TEORT from conversing on a PHF or IHF cell phone (-0.4 and 

3.2% TEORT, respectively). One reason why this was found could be that drivers have hands 

available to perform other secondary tasks when conversing on PHF and IHF cell phones, while 

their hands are occupied when conversing on an HH cell phone. Perhaps drivers were more 

constrained in performing other secondary tasks that demanded visual attention when conversing 

on an HH cell phone. 

The method used to simultaneously browse while conversing on the cell phone was found to 

significantly affect the change in mean percent TEORT, F(2,56) = 3.77, p = .0292. A TukeyKramer test revealed that browsing and conversing on an HH cell phone yielded an increase in 

mean percent TEORT (59.2%) that was significantly greater than the increase in mean percent 

TEORT from browsing and conversing on an IHF cell phone (43.5%). Note that the duration of 

these subtasks is equally important and is reported in the next section. 

6.1.2 TEORT Duration 

The mean TEORT durations for similar subtasks were grouped and compared using a one-way 

between-subjects ANOVA. A significant effect was found, F(9, 651) = 48.99, p < .0001. A 

Tukey-Kramer test revealed that the mean TEORT duration when text messaging (M = 23.3 s) 

was significantly longer than any other subtask (Table 31). Browsing and dialing had TEORT 

durations of 8.2 s and 7.8 s, respectively, which were also found to be significantly longer than 

simpler VM subtasks such as pressing a button to begin an IHF call or ending an HH call. Note, 

the TEORT durations for the conversing subtasks, including simultaneously browsing and 

conversing, were excluded since their sample durations were limited to 6 s. 

Table 31. Mean TEORT Durations Collapsed Across Cell Phone Types 

Subtask Mean TEORT (s) Standard 

Error N 

HH: Text 23.3 A 1.7 207 

HH: Browse/Read 8.2 B, D 0.5 286 

HH: Dial 7.8 B 0.3 405 

PHF: Locate/Put On 2.7 B, C, D 0.9 15 

IHF: Begin/Answer 2.5 C, D 0.4 120 

HH: Locate/Answer 1.3 C, D 0.1 746 

HH: End Task 1.3 C, D 0.1 813 

IHF: End Task 1.3 C, D 0.1 154 

PHF: End Task 0.5 C, D 0.1 33 

PHF: Begin/Answer 0.5 C, D 0.2 13 

 Tukey-Kramer significant differences denoted by capital letters. 

Mean TEORT durations for ungrouped cell phone subtasks were also compared across cell 

phone types using a one-way between-subjects ANOVA. Appendix A12 presents the mean 
 Chapter 6: Investigation of Driver Performance 

TEORT durations for the subtasks that were compared and their respective test statistics. No 

significant differences between the same subtasks were found when comparing across cell phone 

types. 

6.1.3 Speed Standard Deviation 

The mean speed standard deviation of the vehicle when drivers initiated various cell phone 

subtasks above 8 km/h was investigated. Speed standard deviation was computed over the first 

20 s from the start of the subtask. Because this measure could overlap subsequent subtasks, it is 

reported with the intention of investigating the association of specific cell phone subtasks and 

subsequent speed variability. For each subtask and matched baseline sample that had a valid 

speed measure, a one-way within-subject ANOVA was performed to investigate whether the 

mean speed standard deviation when initiating the subtask differed from the mean speed standard 

deviation during the baseline sample. Appendix A12 presents the ANOVA summary results for 

each test. Ending an HH cell phone interaction had a significant effect on the speed standard 

deviation, F(1, 84) = 4.50, p = .0368. The mean speed standard deviation was higher when 

ending an HH cell phone interaction (M = 6.32 km/h, SE = 0.46 km/h, n = 179) than it was 

during the matched baseline sample (M = 4.96 km/h, SE = 0.31 km/h, n = 179). Ending an IHF 

cell phone interaction also had a significant effect on the speed standard deviation, F(1, 43) = 

4.39, p = .0422. The mean speed standard deviation was higher when ending an IHF cell phone 

interaction (M = 5.19 km/h, SE = 0.72 km/h, n = 77) than it was during the matched baseline 

sample (M = 3.95 km/h, SE = 0.41 km/h, n = 77). 

To investigate whether changes in speed standard deviation when performing a subtask differed 

across cell phone types, speed difference scores were created by subtracting the matched baseline 

speed standard deviation from the subtask speed standard deviation. The difference scores were 

grouped by cell phone type and compared using a one-way between-subjects ANOVA. 

Appendix A12 presents the mean speed standard deviation differences for the subtasks and their 

respective test statistics. No significant differences were found. 

6.1.4 Headway Standard Deviation 

The mean headway standard deviation of the vehicle when drivers initiated various cell phone 

subtasks above 8 km/h was investigated. Similarly to speed standard deviation, headway 

standard deviation was computed over the first 20 s from the start of the subtask. For each 

subtask and matched baseline sample that had a valid headway measure, a one-way withinsubject ANOVA was performed to investigate whether the mean headway standard deviation 

when initiating the subtask differed from the mean headway standard deviation during the 

baseline sample. Note that the number of samples available for this analysis was greatly reduced 

when requiring a valid headway measure for both the baseline and subtask samples. For instance, 

a headway measure would not exist if a lead vehicle was not present. Appendix A12 presents the 

ANOVA summary results for each test. No significant differences were found. 

Similarly to speed standard deviation, headway standard deviation difference scores were 

compared across cell phone types using a one-way between-subjects ANOVA. Appendix A12 

presents the mean headway standard deviation differences for the subtasks and their respective 

test statistics. No significant differences were found. 

Final Report 

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 Chapter 6: Investigation of Driver Performance 

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50 

6.1.5 Unintentional Lane Bust Rate 

Unintentional lane busts were analyzed to investigate drivers’ lateral vehicle control. The 

unintentional lane bust rate was computed as the number of unintentional lane busts that 

occurred during the sample interval divided by the duration of the sample interval. Similarly to 

speed standard deviation, a one-way within-subject ANOVA was performed to investigate 

whether the mean unintentional lane bust rate when performing the subtask differed from the 

mean unintentional lane bust rate during the baseline sample. Appendix A12 presents the 

ANOVA summary results. The mean unintentional lane bust rate was significantly lower when 

talking on an HH cell phone (M = 0.001, SE = 0.000, n = 207) compared to baseline (M = 0.003, 

SE = 0.001, n = 207), F(1, 91) = 5.90, p = .0171. 

Unintentional lane bust rate difference scores were compared across cell phone types using a 

one-way between-subjects ANOVA. Appendix A12 presents the mean unintentional lane bust 

rate differences for the subtasks and their respective test statistics. No significant differences 

were found. 

6.1.6 Delayed Reaction to Unexpected External Event 

Table 32 presents the number of samples above 8 km/h in which drivers had a delayed reaction 

to an unexpected external event within 6 s from the start of the sample. An unexpected external 

event was anything unexpected or out of the ordinary that presented a safety hazard (e.g., 

vehicle, pedestrian, or animal unexpectedly entering roadway; this could also have included a 

delayed reaction to a red light). It can be seen that unexpected external events were infrequent 

(only 12 were observed in this study). Consequently, inferential statistics were not performed. 

Table 33 shows which subtasks and baseline periods took place when the unexpected external 

event occurred. Note that baseline periods that had cell phone use take place at some point in the 

20-second interval are included in this table. 

Table 32. Frequency of Driver Delayed Reaction to Unexpected External Event 

Reaction Frequency Percentage 

No external event occurs 6,134 99.80 

Fully prepared, drives appropriately/reacts in a timely manner 9 0.15 

Somewhat caught off guard, but quickly reacts in appropriate manner 3 0.05 

Very much caught off guard, has a delayed reaction (~ > 0.75 s or 750 

timestamps) 

0 0 

Extremely caught off guard, does not react at all 0 0 
 Chapter 6: Investigation of Driver Performance 

Final Report 

51 

Table 33. Frequency of Driver Delayed Reaction to Unexpected External Event by Subtask 

Subtask 

Driver 

Somewhat 

Caught Off 

Guard 

Driver Fully 

Prepared 

No Event 

Occurs 

Baseline - HH -- 2 254 

Baseline - PHF (Complex Subtask Performed at Some Point) -- 1 34 

Baseline - Text 1 1 265 

Baseline - Text (Complex Subtask Performed at Some Point) 1 -- 108 

HH: Holding -- 2 250 

HH: Locate/Answer -- 1 778 

HH: Locate/Answer, IHF: Talk/Listen -- 1 40 

HH: End Task 1 -- 938 

HH: Talk/Listen -- 1 541 

Total 3 9 -- 

6.1.7 Peak Deceleration 

The mean peak deceleration of the vehicle within 10 s of the driver initiating a cell phone 

subtask above 8 km/h was investigated. For each subtask and matched baseline sample that had a 

valid acceleration measure, a one-way within-subject ANOVA was performed to investigate 

whether the mean peak deceleration when initiating the subtask differed from the mean peak 

deceleration during the first 10 s of the baseline sample. Appendix A12 presents the ANOVA 

summary results for each test. The mean peak deceleration was significantly higher when ending 

an HH cell phone interaction (M = 0.105 g, SE = 0.008 g, n = 179) compared to baseline (M =

0.078, SE = 0.007, n = 179), F(1, 84) = 5.51, p = .0212. 

Peak deceleration difference scores were compared across cell phone types using a one-way 

between-subjects ANOVA. Appendix A12 presents the mean peak deceleration differences for 

the subtasks and their respective test statistics. No significant differences were found. 

6.1.8 Driver Performance When Using a Cell Phone near Intersections 

A total of 520 of the 2,108 sampled cell phone interactions consisted of the SV crossing an 

intersection within 10 s from the start of any one of the inherent subtasks. Recall that multiple 

subtasks took place in one cell phone interaction. This equates to 24.7 percent of cell phone 

interactions taking place just prior to crossing an intersection. An intersection was defined here 

as any signalized junction, or junction where the driver’s lane was controlled by a stop or yield 

sign. As a side note, if holding a cell phone or PHF headset/earpiece is included as a subtask, this 

number increases to 553 interactions (26.2%). 

More important, however, is how often drivers use a cell phone near an intersection while the 

vehicle is in motion. A total of 352 (20.1%) of the 1,748 cell phone interactions made when 
 Chapter 6: Investigation of Driver Performance 

traveling above 8 km/h were performed prior to crossing an intersection. When including holding 

as a subtask, this number increases to 379 interactions (21.7%). 

To investigate how using a cell phone affects driver performance near intersections, analyses of 

driver visual behavior and stopping performance were performed using only the cell phone 

interactions that classified into one of the three cell phone types, or were sampled text messages. 

The percentage of subtasks in which the driver scanned before entering the intersection was 

investigated. Scanning was defined as gazing to roadway junctions, but not driveways, 

alleyways, or parking lot entrances. For a 4-way intersection, a glance to the left and right was 

required; for a right 3-way intersection, a glance to the right was required; for a left 3-way 

intersection, a glance to the left was required. These glances were required regardless of traffic 

control status (traffic light color, etc.). Since there were only 455 samples where the vehicle was 

moving near an intersection, all VM subtasks were grouped together, while talking/listening 

alone was categorized separately. It was found that drivers scanned during 37.6 percent of the 

grouped baseline samples (n = 85), 36.1 percent of the grouped VM cell phone subtasks (n = 

269), and 34.6 percent of the grouped talking/listening cell phone subtasks (n = 101). A chisquared test did not find these percentages to significantly differ, χ

2

(2) = 0.1795, p = .9142. 

When considering cases where drivers were required to stop at an intersection within 10 s of 

initiating a subtask, the percentage of subtasks in which the drivers violated the intersection was 

investigated. It was found that drivers had a rolling stop in 86.4 percent of the grouped baseline 

samples (n = 22), 69.7 percent of the grouped VM cell phone subtasks (n = 89), and 68.6 percent 

of the grouped talking/listening cell phone subtasks (n = 35). A chi-squared test did not find 

these percentages to significantly differ, χ

2

(2) = 2.6913, p = .2604. 

6.1.9 Drivers’ Turn Signal Use When Changing Lanes 

There were 232 eligible samples where the SV executed a lane change within 5 s prior to the 

sample and 5 s after the start of the sample. Drivers used their turn signal during this interval of 

time for 51.7 percent of the maneuvers. To explore whether cell phone use affected drivers’ turn 

signal use, the subtasks were grouped into VM subtasks and talking/listening only. 

It was found that drivers used their turn signal during 59.3 percent of the grouped baseline 

samples (n = 59), 52.3 percent of the grouped VM cell phone subtasks (n = 149), and 46.9 

percent of the grouped talking/listening cell phone subtasks (n = 49). A chi-squared test did not 

find these percentages to significantly differ, χ

2

(2) = 1.6937, p = .4288. 

6.2 Driver Adaptation When Using a Cell Phone 

6.2.1 Speed 

The mean speed of the vehicle when drivers initiated various cell phone subtasks above 8 km/h 

was investigated. For each subtask and matched baseline sample that had a valid speed measure, 

a one-way within-subject ANOVA was performed to investigate whether the mean speed when 

initiating the subtask differed from the mean speed at the start of the baseline. Appendix A13 

Final Report 

52 
 Chapter 6: Investigation of Driver Performance 

presents the ANOVA summary results for each test. Browsing while conversing on an IHF cell 

phone had a significant effect on the vehicle’s speed, F(1, 11) = 12.64, p = .0045. The mean 

speed was lower when browsing and conversing on an IHF cell phone (M = 77.5 km/h, SE = 7.1 

km/h, n = 14) than it was during the matched baseline sample (M = 91.5 km/h, SE = 6.2 km/h, n

= 14). It should be noted that the sample size used in these investigations was small. 

Speed difference scores were compared across cell phone types using one-way between-subject 

ANOVAs. Appendix A13 presents the mean speed differences for the subtasks and their 

respective test statistics. The method used to converse had a significant effect on the change in 

speed from baseline, F(2, 162) = 3.09, p = .0481. Although it appears as though drivers 

decreased their speed more when conversing on a PHF cell phone (M = -6.7 km/h, SE = 4.2 

km/h) compared to the other types of cell phones (M = -1.5 km/h, SE = 1.6 km/h, and M = 0.2 

km/h, SE = 2.1 km/h for conversing on HH and IHF cell phones, respectively), a Tukey-Kramer 

multiple comparisons test could not identify where the significant difference existed. It should be 

noted that the observed speed differences may be from drivers choosing to engage in a cell phone 

subtask as they approach a stop. 

6.2.2 Headway 

The mean headway of the vehicle when drivers initiated various cell phone subtasks above 8 

km/h was investigated. For each subtask and matched baseline sample that had a valid headway 

measure, a one-way within-subject ANOVA was performed to investigate whether the mean 

headway when initiating the subtask differed from the mean headway at the start of the baseline. 

Appendix A13 presents the ANOVA summary results for each test. Text messaging had a 

significant effect on the vehicle’s headway, F(1, 27) = 5.03, p = .0405. The mean headway was 

greater when text messaging (M = 0.6 s, SE = 0.1 s, n = 29) than it was during the matched 

baseline sample (M = 0.4 s, SE = 0.1 s, n = 29). It should be noted that the sample size used in 

these investigations was small. At the same time, not having a valid radar measure could be the 

result of engaging in cell phone use when not following a vehicle (i.e., in order for a range value 

to be recorded, there must be a lead vehicle). 

Headway difference scores were compared across cell phone types using one-way betweensubject ANOVAs. Appendix A13 presents the mean headway differences for the subtasks and 

their respective test statistics. No significant results were found. 

6.2.3 TTC 

The mean TTC of the vehicle when drivers initiated various cell phone subtasks above 8 km/h 

was investigated. For each subtask and matched baseline sample that had a valid TTC measure, a 

one-way within-subject ANOVA was performed to investigate whether the mean TTC when 

initiating the subtask differed from the mean TTC at the start of the baseline. Appendix A13 

presents the ANOVA summary results for each test. No significant TTC differences were found. 

6.2.4 SV Lane Change Behavior 

The percentage of subtasks performed above 8 km/h where the SV was observed to change lanes 

(in any direction) in the 10-second interval spanning from 5 s prior to the start of the subtask up 

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 Chapter 6: Investigation of Driver Performance 

Final Report 

54 

to 5 s after the start of the subtask was investigated. For each subtask and matched baseline 

sample, a McNemar change test was performed to investigate whether the proportion of subtasks 

in which the SV changed lanes differed from the proportion of baseline periods in which the SV 

changed lanes. A lane change could be made in either direction for this analysis. Appendix A13 

presents the summary results for each test. Locating/answering an HH cell phone had a 

significant effect on the driver’s likelihood of changing lanes, χ

2

(1) = 6.0000, p = .0227. Drivers 

changed lanes 9.90 percent of the time when locating/answering an HH cell phone (n = 202) 

compared to 3.96 percent of the time during the matched baseline sample (n = 202). Perhaps 

drivers changed lanes when locating the cell phone because they knew they were getting ready to 

make a call and wanted to be in the right lane. 

It was found that drivers changed lanes during 5.1 percent of the grouped baseline samples (n = 

700), 4.5 percent of the grouped VM cell phone subtasks (n = 2992), and 5.2 percent of the 

grouped talking/listening cell phone subtasks (n = 922). A chi-squared test did not find these 

percentages to significantly differ, χ

2

(2) = 1.0378, p = .5952. 

To investigate whether changes in SV lane change behavior when performing a subtask differed 

across cell phone types, the samples were grouped into the following three categories: 

1. SV changed lanes during subtask, but not during baseline 

2. SV changed lanes in both baseline and subtask, or SV did not change lanes in both 

baseline and subtask 

3. SV changed lanes during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types 

using a chi-squared test. Appendix A13 presents the percentage of samples for each of the three 

categories and the respective p-value. The method used to end the cell phone use was found to be 

significantly related to the SV lane change behavior (Table 34). 

Table 34. Results for Between-Subjects Comparisons of SV Lane Change Behavior When 

Ending Cell Phone Use Across Cell Phone Types 

Subtask 

SV LC During 

Subtask, but 

Not During 

Baseline 

(%) 

Same LC 

Behavior During 

Baseline and 

Subtask (%) 

SV LC During 

Baseline, but Not 

During Subtask 

(%) 

n df χ2 p-value

HH: End Task 1.40 96.65 1.96 358 4 11.7721 .01913 

PHF: End Task 0.00 88.89 11.11 9 4 11.7721 .01913 

IHF: End Task 3.95 88.16 7.89 76 4 11.7721 .01913 

LC – lane change 

6.2.5 SV Lane Position 

The percentage of subtasks performed above 8 km/h where the SV was traveling in the rightmost lane when initiating the subtask was investigated. For each subtask and matched baseline 
 Chapter 6: Investigation of Driver Performance 

sample, a McNemar change test was performed to investigate whether the proportion of subtasks 

in which the SV traveled in the right-most lane differed from the proportion of baseline periods 

in which the SV traveled in the right-most lane. Appendix A13 presents the summary results for 

each test. No significant differences were found. 

It was found that the SV traveled in the right-most lane during 39.6 percent of the grouped 

baseline samples (n = 477), 38.6 percent of the grouped VM cell phone subtasks (n = 1850), and 

39.9 percent of the grouped talking/listening cell phone subtasks (n = 554). A chi-squared test 

did not find these percentages to significantly differ, χ

2

(2) = 0.3558, p = .8370. 

To investigate whether changes in SV lane position behavior when performing a subtask differed 

across cell phone types, the samples were grouped into the following three categories: 

1. SV in right-most lane during subtask, but not during baseline 

2. SV in right-most lane for both baseline and subtask, or SV not in right-most lane for both 

baseline and subtask 

3. SV in right-most lane during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types 

using a chi-squared test. Appendix A13 presents the percentage of samples for each of the three 

categories and the respective p-value. No significant differences were found. 

6.3 Downstream Effects From Drivers Using Cell Phones 

6.3.1 Range to Rear Vehicle 

The percentage of subtasks performed above 8 km/h where the Rear Vehicle (RV) was rated to 

be traveling closely behind the SV (less than 20 m) at the start of the subtask was investigated. 

For each subtask and matched baseline sample, a McNemar change test was performed to 

investigate whether the proportion of subtasks in which the RV was close differed from the 

proportion of baseline periods in which the RV was close. Appendix A14 presents the summary 

results for each test. No significant differences were found. 

It was found, however, that an RV was close to the SV during 6.2 percent of the grouped 

baseline samples (n = 338), 9.8 percent of the grouped VM cell phone subtasks (n = 1,387), and 

12.3 percent of the grouped talking/listening cell phone subtasks (n = 454). A chi-squared test 

found these percentages to significantly differ, χ

2

(2) = 8.2123, p = .0165. It should be noted that 

this result could be a downstream effect from drivers using a cell phone, or it could be a 

reflection of the types of conditions during which drivers use a cell phone. 

To investigate whether the likelihood of the RV traveling close to the SV when performing a 

subtask differed across cell phone types, the samples were grouped into the following three 

categories: 

1. RV traveling close to SV during subtask, but not during baseline 

Final Report 

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 Chapter 6: Investigation of Driver Performance 

2. RV traveling close to SV for both baseline and subtask, or RV not traveling close to SV 

for both baseline and subtask 

3. RV traveling close to SV during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types 

using a chi-squared test. Appendix A14 presents the percentage of samples for each of the three 

categories and the respective chi-square p-value. No significant differences were found. 

6.3.2 Rear Vehicle Lane Change Behavior 

The percentage of subtasks performed above 8 km/h where the RV executed a lane change to 

pass the SV within 5 s prior to the start of the subtask up to 5 s after initiating the subtask was 

investigated. For each subtask and matched baseline sample, a McNemar change test was 

performed to investigate whether the proportion of subtasks in which the RV passed the SV 

differed from the proportion of baseline periods in which the RV passed the SV. Appendix A14 

presents the summary results for each test. No significant differences were found. 

It was found that an RV passed the SV during 3.9 percent of the grouped baseline samples (n = 

337), 3.2 percent of the grouped VM cell phone subtasks (n = 1,386), and 2.2 percent of the 

grouped talking/listening cell phone subtasks (n = 453). A chi-squared test did not find these 

percentages to significantly differ, χ

2

(2) = 1.8799, p = .3907. 

To investigate whether the likelihood of the RV passing the SV when performing a subtask 

differed across cell phone types, the samples were grouped into the following three categories: 

1. RV passed the SV during subtask, but not during baseline 

2. RV passed the SV for both baseline and subtask, or RV did not pass the SV for both 

baseline and subtask 

3. RV passed the SV during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types 

using a chi-squared test. Appendix A14 presents the percentage of samples for each of the three 

categories and the respective chi-square p-value. No significant differences were found. 

Final Report 

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Chapter 7: Discussion 

7 Discussion 

This study was performed to generate information on drivers’ cell phone use, the SCE risk 

associated with cell phone use, and driver performance when using a cell phone. In addition to 

generating updated statistics on drivers’ HH cell phone use based on naturalistic driving data, 

drivers’ use – and the associated SCE risk – of PHF and IHF cell phones was also investigated. 

A key aspect of this study was the incorporation of drivers’ cell phone records, and the detailed 

reduction of cell phone subtasks while driving, in the investigations. 

7.1 Drivers’ Cell Phone Use 

By overlaying the cell phone records with the collected naturalistic driving data, drivers were 

found to have talked on a cell phone 10.6 percent of the time the vehicle was operated. Although 

this estimate is based on drivers who reported substantial cell phone use while driving (at least 

one call while driving per day), and call records that rounded up to the nearest minute, it 

provides a generally robust estimate. 

To help put this finding into perspective, Table 35 summarizes cell phone use estimates 

presented in earlier studies. The 100-Car Study estimates in the table are those reported in this 

report’s introductory section on drivers’ cell phone use. They, in addition to the use statistics 

reported in the Olson et al. (2009) investigation of commercial driver distraction, were generated 

through an analysis performed in the current study that examined the percentage of baseline and 

SCE samples that had specific cell phone subtasks observed in the 6-second interval (note: the 

cell phone use statistics are not the percentage of “just driving” samples, but rather the 

percentage of all samples). Since the current study sampled 2,308 baseline periods and 342 SCEs 

in a similar manner to the earlier NDSs (based on drivers’ time in study) the percentage of 

samples in which the cell phone subtasks were observed can be compared (Table 35). Key 

patterns that emerge include the following. First, drivers in the current study were estimated to 

talk on any type of cell phone 10.8 percent of the time through the case-control sampling 

methodology, and 10.6 percent of the time using the call records (risk rate approach). This 

indicates that the case-control sampling methodology was relatively accurate. Second, compared 

to the 100-Car Study, drivers in the current study appear to have talked less on an HH cell phone, 

talked more on hands-free cell phones, dialed less on an HH cell phone, but texted more on HH 

cell phones. Third, the current study’s estimates for talking on an HH cell phone are generally in 

line with the NOPUS estimates. Finally, it is important to note that text messaging was observed 

in the current study, despite it being illegal to do so in the states where drivers were observed. 

Final Report 

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Chapter 7: Discussion 

Final Report 

58 

Table 35. Estimates of Drivers’ Cell Phone Use (Dashes Indicate Unavailable Data) 

Study Year Data 

Collected

Cell Phone 

Use 

(Collapsed)

Text Dial HH 

Talk/Listen

HF

Talk/Listen

100-Car Study 

(Klauer et al., 2006) 2003-2004 8.3% - 1% 

7.6% 

6.2% 1.3% 

Two-Truck NDS 

(Olson et al., 2009) 

2004-2005 

2005-2007 9.2% 0.1% 1% 

8.3% 

4.2% 4.1% 

IVBSS 

(Funkhouser & Sayer, 2012) 2006 

6.7% 

(Includes 

stopped 

vehicles) 

- - - - 

NOPUS (National Highway 

Traffic Safety Administration, 

2011) 

2010 9%*

 0.9% 0.9% 5% 4%*

Current Study 

(Based on Cell Phone Records) 2011 - - - 

10.6% overall 

10.4% > 8 km/h 

13.0% < 8 km/h 

Current Study 

(Based on SCE-Baseline 

Samples) 

2011 15.7% 3.0% 0.3% 

10.8% 

4.8% 3.6% PHF 

2.45% IHF 

* Estimated using NHTSA’s 2007 Motor Vehicle Occupant Safety Survey (MVOSS) data (National Highway Traffic 

Safety Administration, 2011) 

This study found that drivers who had access to PHF cell phones made more calls per driving 

minute than did drivers who had access to IHF cell phones or who only made calls on HH cell 

phones. It is unclear whether drivers purchased PHF cell phones because they recognized that 

they frequently made calls and required an HF technology to meet this need, or whether drivers 

made more calls with PHF cell phones because the interface made it easier to do so. PHF cell 

phones allow drivers to initiate calls with one button press and/or a voice-command, which 

requires significantly less VM attention than does locating and dialing on an HH cell phone. 

In line with this thinking, it was also found that calls made on PHF cell phones lasted 

significantly longer (M = 5.0 minutes) than calls made on IHF cell phones (M = 3.8 minutes) 

and HH cell phones (M = 3.0 minutes). The HF technology not only makes it easier to initiate 

calls, but also easier to continue a conversation. Drivers can keep their hands on the wheel, and 

do not get fatigued from holding a cell phone to their ear. Again, it is to be determined whether 

PHF usage was greater because of the type of drivers that made the calls, or because the interface 

simplified cell phone interaction. Although PHF and IHF both allow hands-free conversation, the 

duration of PHF calls may have been longer because of the types of drivers that purchase this 

technology. 

Despite the benefits that HF cell phones offer (from minimizing the need to reach for, dial, and 

hold a cell phone while driving), the data show that drivers still used an HH cell phone during 

PHF and IHF calls. For instance, PHF drivers used an HH phone for at least one subtask in 55.5 
Chapter 7: Discussion 

percent of PHF phone interactions. IHF drivers used an HH phone for at least one subtask in 53.2 

percent of IHF phone interactions. This clearly indicates that the technology has not eliminated 

the visual distraction imposed from HH cell phone use. Reasons why drivers continued to use 

HH cell phones during use could be: (1) the HF technology did not reliably comprehend the 

drivers’ voice commands and thus necessitated manual dialing, (2) the technology did not 

automatically pair with the drivers’ cell phone and thus required manual interaction to pair the 

cell phone, and (3) drivers could not remember the name of the contact (as entered in their 

address book) and thus had to manually locate the contact in their address book. A fourth reason, 

and most concerning, is that the HF cell phones allowed drivers to browse and text during a 

conversation. However, this feature is not limited to HF cell phones. Drivers were observed to 

browse and talk using HH cell phones (either using a speaker-phone feature, or simply 

disengaging the phone from their ear to browse). Nevertheless, it was found that drivers browsed 

on an HH cell phone while conversing on an IHF cell phone significantly longer than they 

browsed and conversed on an HH cell phone. This could be due to the ease with which the 

technology makes dual tasking possible. 

The non-cell-phone-related secondary task “eating/drinking” did occur significantly more often 

in IHF subtasks (0.58%) than in HH subtasks (0.15%) (p = 0.0311); however, the difference is 

marginal at 0.43 percentage points. No significant differences were found in the prevalence of 

non-cell-phone-related secondary tasks across the cell phone types. It was believed that drivers 

might have engaged in other activities more frequently when using the HF cell phones, but this 

was not found to be the case. 

The average amount of time drivers took to text/browse when traveling above 8 km/h was 1.3 

minutes. This included the time taken to locate the HH cell phone, browse to the text messaging 

interface, text (i.e., input the text message, which was – on average –34.6 s), and end the task by 

placing the cell phone down. This represents a substantial amount of time spent performing 

consecutive VM subtasks. Despite the fact that text messaging is illegal in the states where the 

study was performed, the data suggest that drivers continue to text for extended durations. 

Drivers’ cell phone use was compared across low and high driving task demands to explore how 

cell phone use may be affected by the driving context. There were subtasks that were 

significantly shorter during high driving task demands than in low driving task demands. These 

included browsing, text messaging, ending an IHF call, and ending a PHF call. This may be 

evidence of drivers curtailing cell phone use when driving demands more of their attention. 

7.2 SCE Risk Associated With Cell Phone Use 

Talking on any type of cell phone was not found to be associated with an increased SCE risk. 

This was the case when assessing SCE risk relative to general driving using a risk rate approach, 

and when assessing SCE risk relative to “just driving” using a case-control approach. However, 

VM subtasks were associated with an increased SCE risk. The risk rate approach estimated VM 

subtasks (collapsed across all VM subtasks) to be associated with a significantly increased SCE 

risk relative to general driving (OR = 2.93), and the case-control approach estimated that they 

were associated with a significantly increased SCE risk relative to “just driving” (OR = 1.73). 

These findings are in alignment with previous NDS investigations of SCE risk related to cell 

Final Report 

59 
Chapter 7: Discussion 

phone subtasks (Fitch & Hanowski, 2011; Hickman, Hanowski, & Bocanegra, 2010; Klauer et 

al., 2006; Klauer et al., 2010; Olson et al., 2009). 

The SCE risks associated with the three types of cell phone interfaces were also investigated. 

Here, the SCE risk associated with HH cell phone use (collapsed across subtasks) was found to 

significantly increase using the risk rate approach (OR = 1.73). This was because the SCE risk 

related to the VM subtasks outweighed the SCE risk related to conversing on an HH cell phone. 

Both call-related VM subtasks and text-messaging were associated with a significantly increased 

SCE risk (ORs = 3.34 and 2.12, respectively). These findings reinforce the dangers of drivers 

taking their eyes off the road to interact with a cell phone. 

The SCE risks associated with PHF and IHF cell phone use (when all HH VM cell phone 

subtasks were excluded) were not found to significantly increase. It must be recognized, 

however, that pure PHF and IHF cell phone use did not always take place: 55.5 percent of the 

218 sampled PHF interactions and 53.2 percent of the 344 sampled IHF interactions involved 

VM HH subtasks. VM HH cell phone interactions could include pairing the cell phone with the 

device, manually dialing when a voice command was not successful, and text 

messaging/browsing during the call. 

7.3 Driver Performance While Using a Cell Phone 

Driver performance when using a cell phone was investigated in terms of visual behavior, 

longitudinal vehicle control, lateral vehicle control, and reaction to unexpected external events. 

Drivers’ lane change performance, performance when near intersections, and the effect that 

drivers using cell phones have on downstream traffic were also investigated. Overall, the results 

complement the SCE risk findings in that VM subtasks performed on an HH cell phone affected 

drivers’ visual behavior and vehicle control, while talking on a cell phone did not degrade 

driving performance. 

The root of driving performance lies in how well drivers visually attend to the road in order to 

perceive events when they occur. Drivers’ visual attention to the forward roadway was 

substantially affected by VM subtasks performed on an HH cell phone. Locating, dialing, text 

messaging, browsing, and ending an HH call all increased the percentage of TEORT compared 

to baseline. Furthermore, text messaging (M = 23.3 s), browsing (M = 8.2 s), and dialing (M =

7.8 s) all led to substantially longer TEORT durations than when drivers performed PHF and IHF 

cell phone subtasks. To compare, the largest mean TEORT was 2.7 s when locating a PHF 

device. Long TEORT durations are a concern as they can degrade drivers’ ability to quickly 

perceive events in the roadway. 

It is interesting that locating an HH cell phone was found to increase SCE risk through the casecontrol analysis because drivers had a relatively short mean TEORT duration (M = 1.3 s) when 

performing this subtask. This suggests that drivers may have been selective in terms of when 

they took their eyes off the road to text, browse, and dial, while they may have used less 

discretion when locating an HH cell phone. This is particularly plausible when considering that 

locating a cell phone to answer an incoming call has an inherent urgency. 

Final Report 

60 
Chapter 7: Discussion 

When crossing an intersection, drivers properly scanned the intersection 38 percent of the time 

when not using a cell phone. Their likelihood of scanning the intersection did not change when 

performing either VM or talking/listening subtasks. When stopped at an intersection, however, 

drivers that used a cell phone were less likely to scan the intersection prior to advancing. It must 

be noted, however, that this later finding was produced using 23 observations of drivers stopped 

at an intersection. As such, there are insufficient data for it to be generalized and a more robust 

investigation based on a sufficiently large sample size is warranted. 

The effects of cell phone use on vehicle control were, in contrast to visual behavior, much less 

pronounced. Ending both HH and IHF cell phone use was associated with a significantly higher 

speed standard deviation compared to baseline (as computed over 20 s from the start of subtask). 

Ending HH cell phone use was also associated with a significantly higher peak deceleration 

compared to baseline. Although it is possible that drivers braked harder because they were 

distracted by their cell phone use, it is also possible that drivers chose to end their cell phone 

conversations when coming to a stop (e.g., in their driveway) or when nearing their destination 

(e.g., in a parking lot). Another finding was that locating an HH cell phone was performed more 

frequently when the SV changed lanes. Performing this subtask while changing lanes may be 

another reason why locating an HH cell phone was found to be associated with an increased SCE 

risk. 

There were two findings that could be construed as evidence of compensatory behavior when 

using a cell phone. First, browsing was performed at significantly lower speeds than the speeds 

recorded during baseline. Second, text messaging was performed at significantly greater 

headways than the headways recorded during baseline. It must be noted, however, that the 

sample size pertaining to these findings was quite small, making it difficult to generalize the 

findings. For the most part, drivers did not decrease their speed when performing VM or 

talking/listening cell phone subtasks. Similar results were found when analyzing commercial 

motor vehicle speed when drivers engaged in mobile device use (Fitch & Hanowski, 2012). 

With respect to assessing whether cell phone use affected downstream traffic behavior, the data 

indicate that a trailing vehicle was more likely to be traveling close (less than 14 m) to the SV 

when the driver was performing either VM or talking/listening subtasks on a cell phone. 

Although a first thought might be that drivers using a cell phone were not keeping pace with lead 

vehicles, the analyses of vehicle speed and headway did not overwhelmingly indicate that this 

was the case. What may be more likely to have taken place was that drivers used their cell 

phones in situations where vehicles traveled closer together (e.g., in stop-and-go traffic). Further 

analysis should be performed to better understand the contexts in which drivers used their cell 

phones to properly interpret this finding. 

A goal of this study was to investigate the effects of distraction from “just talking” on a cell 

phone. It was found that talking on an HH cell phone increased drivers’ visual attention to the 

forward roadway and improved their lane keeping performance. Talking on a PHF or IHF cell 

phone was not found to impact any of the driver performance measures investigated. An 

exploratory analysis did not find drivers’ scanning behavior when crossing an intersection, their 

tendency to have a rolling stop at an intersection, or their tendency to signal during lane change 

maneuvers to change when talking on cell phone. Albeit, these latter investigations precluded 

performing matched comparisons due to a small sample size. Finally, emotional conversation 

Final Report 

61 
Chapter 7: Discussion 

was qualified using FACS to explore the potential impact of intense emotional conversation on 

driving. Emotional conversation took place in 3.6 percent of the samples. Although an 

investigation of SCE risk from emotional conversation did not find an effect, the analysis was 

limited to the small sample size available. Overall, none of the analyses performed in this study 

found talking on a cell phone to lead to a driving performance decrement. 

7.4 Summary 

The results from this study present a clear finding: VM subtasks performed on HH cell phones 

degrade driver performance and increase SCE risk. Talking on a cell phone, regardless of the 

type of interface, was not associated with an increased SCE risk. Pure PHF and IHF cell phone 

use – where VM HH cell phone subtasks are excluded – were also not associated with an 

increased SCE risk. Although current HF interfaces allow drivers to communicate with their 

voice, there is a concern that they still allow, and sometimes require, VM HH cell phone 

subtasks. Drivers can, and frequently do, initiate HF calls, text/browse during HF calls, and end 

HF calls with an HH cell phone. HF interfaces also require that drivers enable a Bluetooth 

connection, pair their cell phone, and manually dial if their voice commands are not recognized. 

Approximately half of the hands-free cell phone interactions in this study were found to involve

a VM HH cell phone subtask. Such VM HH cell phone subtasks detract from the goal of true HF 

cell phone use. Furthermore, there is a segment of the driving population which primarily uses a 

cell phone to exchange text messages. Various HF interfaces do not address this type of cell 

phone use. 

Final Report 

62 
 Chapter 8: Limitations 

8 Limitations 

The following limitations could have potentially impacted the study’s ability to answer the 

research questions. First, the cell phone records only documented sent and received calls and text 

messages. Time when the driver was browsing on the cell phone, or simply holding the cell 

phone, could not be identified without a video reduction. Although it may have been possible to 

use the data transfer records to estimate when browsing took place, such records would be 

inaccurate because of cell phone applications operating in the background when the phone was 

not being used. This limitation may have affected the risk rate approach’s estimate of general 

driving. Second, not all drivers provided call and text records. Out of the 204 drivers in the 

study, call records were available for 187 drivers and text records were available for 109 drivers. 

As such, the cell phone use reduction was used to estimate how the drivers that did not provide 

text records performed text messaging subtasks in the risk rate approach. Third, this study 

estimated driver performance when talking on a cell phone using randomly selected 6-second 

samples in which talking was the only cell phone subtask that took place. A reduction of the 

entire talking subtask was not performed because the study timeline made this infeasible. 

Although the majority of dependent measures were used to investigate instantaneous driving 

performance, this limitation may have affected the study’s ability to assess driver performance 

when talking on a cell phone. Fourth, this study reported the percentage of cell phone use near an 

intersection. To truly understand cell phone use near intersections, however, would require 

knowing how frequently drivers were near an intersection when not using a cell phone. Finally, 

there were very few samples of drivers engaging in emotional conversation, or interacting with a 

cell phone while stopped at an intersection, to perform robust inferential tests. Further sampling 

is required to investigate these aspects. 

Final Report 

63 

 Chapter 9: Acknowledgements 

9 Acknowledgements 

The following people are greatly thanked for their support in data acquisition installation and 

data collection: Laura Tollin, Kelly McGowan, Logan Donnelly, Todd Smith, David 

Mellichamp, Scott Stone, Scott Aust, Stephen Tucker, Alexander Bier, Tammy Russell, Carl 

Cospel, Julie Jermeland, Jared Bryson, Andrew Petersen, Sally Waldon, and Doug McGraw. The 

authors also wish to acknowledge Jim Jenness, Neil Lerner, and other individuals who are a part 

of the Westat team for providing commendable assistance with data collection. The following 

individuals provided invaluable assistance with data reduction: Rebecca Olson, Megan Moore, 

Sarah Terrell, Holland Vasquez, Heather Poole, Laura Meadows, Brandy Puryear, William 

Johnson, April Thompson, Jessica Maitland, Danielle Dougherty, Lora Howard, Carrie Boucher, 

Arielle Brassard, Ben Boucher, Lama Hasan, Rebecca Rader, Caitlin Johnson, Esther Jung, Anne 

Dumadag, Richard Walton, Collin Lester, Diana Trump, Timothy Walker, Evan Tatarka, Erem 

Memisyazici, Lauren Cupp, Adam Thompson, Matthew Frazier, Heather Calhoon, Boon Teck 

Ong, Jessica Chesnakas, Karine Johnson, Tameka Byrd, Hannah Miller, Wesley Hill, Ryan 

Knight, Padma Carstens, Rachel Harris, Erem Memisyazici, and Spencer Henry. Kim Shelton 

and Spencer Joslin are thanked for their project management assistance. Vikki Fitchett’s 

technical editing of final deliverables was also greatly appreciated. 

Final Report 

65 

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Final Report 

70 
 Appendices 

APPENDICES 

A.1 Data Elements and Dependent Measures 

A.2 Cell Phone Provider Billing Policies 

A.3 Operational Definitions for Cell Phone Subtasks 

A.4 Driver, Vehicle, and Environmental Factors Coded for Cell Phone Subtasks 

A.5 Definition of Eyeglance Locations 

A.6 Subtask-Level Kinematic Data 

A.7 Driver, Vehicle, and Environmental Questions for Safety-Critical Events 

A.8 Characterization of Safety-Critical Events 

A.9 Driver, Vehicle, and Environmental Questions for Safety-Critical Event Baseline Periods 

A.10 Investigation of Driver’s Cell Phone Use 

A.11 Risk Rate Approach Estimation Details 

A.12 Driver Performance ANOVA Results 

A.13 Driver Adaptation ANOVA Results 

A.14 Downstream Effects From Drivers Using a Cell Phone ANOVA Results 

A.15 Exploratory Analyses 

Final Report 

71 
 Appendix A.1 Data Elements and Dependent Measures 

Final Report 

72 

A.1 Data Elements and Dependent Measures 

Table 36. Data Elements and Dependent Measures 

Data Element Dependent Measures 

Captured Units Sampling Frequency 

Camera: Driver head and torso 

 Cell phone use/subtask 

 Eye glance location 

 Eyes-off-road 

 Seat belt use 

 Other in-vehicle secondary 

tasks 

 Partial view out driver side 

window 

N/A 15 Hz 

Camera: View of forward 

roadway 

 Driving context 

 Safety-critical events 

N/A 15 Hz 

Camera: View of vehicle 

console, steering wheel, and 

driver lap 

 Cell phone use/task 

 Hands on steering wheel 

 Other vehicle feature 

interactions 

N/A 15 Hz 

Camera: View of rearward 

roadway 

 Safety-critical events 

 Rear vehicle behavior 

N/A 15 Hz 

Accelerometers  Aggressive driving 

 Safety-critical events g 10 Hz 

GPS  Clock time 

 Vehicle location, elevation 

ms, deg, m 1 Hz 

Forward radar 

 Forward object 

identification 

 Object range 

 Object range rate 

 Safety-critical events 

m, m\s 12.5 Hz 

Lane tracker 

 Vehicle’s distance to the 

lane markings 

 Lane busts 

cm 15 Hz 

Illuminance sensor  Ambient light level lux 10 Hz 

Vehicle network data from 

OBD-II port 

 Vehicle speed 

 Brake application 

 Steering wheel position 

 Other measures as available 

depending on vehicle model 

Varies Varies 
 Appendix A.2 Cell Phon

Final Report 

73 

A.2 Cell Phone Provider Billing Policies 

Question Verizon AT&T Boost Mobile T-Mobile Sprint US Cellular NTel

When determining call length, do you round to the nearest minute? Yes Yes Yes Yes Yes Yes YeDo you round up, or down? Up Up Up 

0.5 rounded up, 

below rounded 

down 

Up Up Up 

If I make a call and the call is not answered, will those minutes appear on my call log? 

Yes Yes No Yes No No No – u

60s rin

If I make a call and their voice mail picks up, will those minutes appear on my call log? 

Yes Yes Yes Yes Yes Yes Ye

If I receive a call but do not answer it, will those minutes appear on my call log? 

No Yes - missed call No Yes No No No – u

60s rin

If I miss a call and the person calling leaves me a voice message, will those minutes appear on my call log? 

No Yes Yes Yes Yes No Ye

If I check my voicemail, will those minutes appear on my call log? Yes Yes Yes Yes Yes Yes YeNumber of participants with cell phone provider 106 38 1 7 28 8 2 
 Appendix A.3 Operational Definitions 

Final Report 

74 

A.3 Operational Definitions for Cell Phone Subtasks 

In the first step of the Cell Pilot Analysis, suspected cell phone interactions were identified 

within the driving data based on a review of sampled cell phone records provided by participants. 

Reductionists reviewed these suspected cell phone interactions to identify the true beginning and 

ending of the each interaction. This protocol describes the individual cell phone subtasks coded 

within these interactions (e.g., reaching, dialing, talking, browsing) through a video reduction 

interface. These subtasks then provided structure for the remaining analyses required by the 

project. 

Multiple tasks often occurred simultaneously, and any simultaneous tasks were coded together 

(i.e., all simultaneous tasks were captured in the coding). Before coding subtasks for any given 

event, reductionists determined the high level tasks being performed (e.g., text sent or received, 

call made or received) from the phone records to provide context for the subtasks. 

Also, time periods where both of the driver’s hands were off the wheel were coded as well, 

although this may or may not be related to the cell phone task being performed at the same time. 

Cell Phone Subtask List 

Hand-Held: Locate/Reach/Answer 

Hand-Held: Talk/Listen/Voice Commands 

Hand-Held: Dialing 

Hand-Held: Text Messaging 

Hand-Held: Viewing/Browsing/Reading 

Hand-Held: Holding 

Hand-Held: End Task 

Integrated Hands-Free: Press Button to Begin/Answer 

Integrated Hands-Free: Talk/Listen/Voice Commands 

Integrated Hands-Free: Press Button to End 

Portable Hands-Free: Locate/Put-on Headset/Earpiece 

Portable Hands-Free: Holding/Wearing Headset/Earpiece 

Portable Hands-Free: Push Button to Begin/Answer 

Portable Hands-Free: Talk/Listen/Voice Commands 

Portable Hands-Free: Push Button to End 

Cell Phone Navigation 

Other Cell Phone Task 

Both Hands off Steering Wheel 

Cell Phone Use Subtask Definitions 

Hand-held: Locate/reach/answer- When the driver looks for or reaches towards his/her handheld cell phone. If more than one step occurs (i.e., driver looks for phone, reaches for it, then 

answers it), the first frame number coded would be the start of the first task (i.e., looking before 

reaching for the phone) and the last frame number coded would be the end of the last task (i.e., 

answering phone). 
 Appendix A.3 Operational Definitions 

NOTE: If the subject must remove a hand-held cell phone from the case before using it, 

codes as “HH: locating/reaching/answering.” 

o Event Start - when the driver starts to move his/her hand in the direction of the 

hand-held phone in order to retrieve the phone OR first glances in the direction of 

the hand-held phone followed by immediately reaching for it, whichever comes 

first. If the driver adjusts radio or HVAC prior to initiating the cell phone task, 

then the first movement or glance toward the HVAC/radio should be coded as 

Event Begin.

o Event End - when the driver does one of the following (or whichever comes last): 

1. For answering the hand-held cell phone, the last frame coded is when the 

driver finishes moving the phone to his/her ear. 

2. For locating and reaching for the hand-held cell phone, the last frame 

coded is when one of the other categories begins (i.e., “HH: dialing,” 

“HH: talk/listen/voice commands”). So if reaching is followed by 

dialing, then reaching would end when the phone is first flipped/slid open, 

or for non-flip phones, when the first button is depressed. And lastly, it 

could be when the driver’s hand becomes stationary again. If the driver 

picked up a hand-held phone, but then rests the phone in lap, no cell phone 

task would follow. If the driver picks up the phone and just holds the 

phone in hand without further visual or manual interaction for 5 or more 

seconds, “HH: Holding” would follow. In this last case, “HH: 

Locate/Reach/Answer” would end and “HH: Holding” would begin at the 

beginning of the 5-second rule. (See HH: Holding section for complete 

definition.) 

3. For locating cell phone and not picking it up, the last frame number coded 

would be the first frame number where the subject has shifted his/her gaze 

AND hands to something else (i.e., forward roadway/steering wheel) after 

having glanced at or reached for the cell phone for the last time. 

Hand-Held: Talk/Listen/Voice Commands- When a driver is talking on a hand-held phone or 

has the phone up to his/her ear as if listening to a phone conversation or waiting for the person 

being called to pick up the phone. 

NOTE: If the driver uses the speaker phone function on a hand-held cell phone, code as 

“HH: Talk/Listen/Voice Commands” if the driver keeps the hand-held phone in his/her 

hand(s) while using the speaker phone function. Code as “PHF: Talk/Listen/Voice 

Commands” if the driver puts the phone down (thus, does NOT hold it in his/her hand(s)) 

while using the speaker phone function. 

o Event Start - when the phone is at the driver’s ear OR (in cases of hand-held 

speaker phone) when the driver begins talking repeatedly with no obvious 

passenger interaction

o Event End - when the driver: 

1. moves the phone away from his/her ear to end a call (coded as “HH: End 

Task ” until the phone fully leaves the driver’s hand(s)), 

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 Appendix A.3 Operational Definitions 

2. OR once the driver moves the phone away from his/her ear, and continues 

to hold the phone in his/her hand(s) without further visual or manual 

interaction for 5 consecutive seconds. This should be coded as “HH: 

Holding” until the driver begins another task with the phone or the phone 

fully leaves the driver’s hand(s). “HH: Talk/Listen” would end and “HH: 

Hold” would begin at the start of this 5-second rule. (See HH: Holding 

section for complete definition.) 

Hand-held: Dialing - When the driver is pressing buttons or interacting with a touch screen on 

a hand-held cell phone in order to dial a phone number to make a call. This can include dialing, 

searching for a contact’s number, entering a voice mail password, etc. 

NOTE: This option was only used when the cell records indicate that the driver had 

made an outgoing phone call. 

NOTE: This does NOT include pressing a button to answer a call (coded as “HH: 

Locating/Reaching/Answering”) or pressing a button to end a call (coded as “HH: End 

Task”). 

NOTE: Additionally, “HH: Dialing” does NOT include pressing buttons or interacting 

with a touch screen in order to type/read a text message (which should be coded as “HH: 

Text messaging” if driver types or “HH: Viewing/Browsing/Reading” if driver reads) or 

browse the Internet/use phone applications (which should be coded as “HH: 

Viewing/Browsing/Reading”).

o Event Start - For flip/slider phones it begins when driver flips/slides open the 

phone OR first glances at the phone immediately before flipping it open in order 

to dial, whichever comes first. For non-flip phones, it begins when the driver first 

depresses a button on the keypad or touchscreen OR first glances at cell phone 

followed immediately by pushing a button, whichever comes first. If the driver 

reads a number off a paper, the task begins when he/she reaches for paper OR first 

glances at it/looks for it. If the driver adjusts radio or HVAC prior to initiating the 

cell phone task, then the first movement or glance toward the HVAC/radio should 

be coded as Event Begin.

o Event End – After the last button is depressed and the driver starts a new task 

(e.g., “HH: Talking/Listening/Voice commands” or “PHF: 

Talking/Listening/Voice Commands”), OR when the driver closes the phone 

and/or lets it go, OR the driver last glances at the phone before moving on to a 

new task, whichever comes last.

Hand-held: Text messaging- When a driver is pushing buttons or interacting with a touch 

screen on a hand-held cell phone in order to type a text message. 

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 Appendix A.3 Operational Definitions 

NOTE: This option was only used when the cell records indicate that the driver has sent 

a text message on a hand-held phone. 

NOTE: This does not include reading a text message, which should be coded as “HH: 

Viewing/Browsing/Reading.” 

NOTE: If the cell records indicated that the driver has received a text message, and the 

driver is seen checking then replying to this text message in the video, event is coded as 

follows: If the driver replies to the text message within 10 seconds after reading the text 

message, then the reply should be considered part of the same task, and was coded as 

“HH:Text” (the initial reading of the received text message was coded as 

“HH:View/Browse”). If the driver does NOT reply to the text message within 10 seconds 

and simply holds the phone (coded as “HH:Hold”) for 10+ seconds or puts the phone 

down (coded as “HH:End Task”), then the sent text should be considered a separate, nonsampled task and was not coded. 

o Event Start – For flip/slider phones, it begins when the driver flips/slides open the 

phone OR first glances at the phone immediately before flipping it open in order 

to begin a text message, whichever comes first. For non-flip phones, it begins 

when the first button on the keypad/touchscreen is depressed to begin a text 

message OR when the driver first glances at the cell phone followed immediately 

by pushing a button, whichever comes first.

o Event End - After the last button is depressed and the driver moves on to a new 

task (e.g., “HH: End Task,” etc.), OR the driver last glances at the phone as if 

checking that the message was sent before moving on to a new task, whichever is 

last (Note: the lowering/closing of the phone and putting it down if contiguous to 

this should be coded as “HH: End Task”).

Hand-Held: Viewing/Browsing/Reading – When the driver views the hand-held cell phone 

display with or without pressing buttons or manipulating the touch screen for a purpose other 

than making/receiving a call or sending a text message. Examples include: when the driver uses 

the cell phone to check time, read a received text message, browse the Internet or email, or use 

the phone’s other applications. 

NOTE: If any viewing and/or button manipulation is seen and there is NO record of a 

call being made/received/ended or a text being sent, then use this category. Reading a 

received text messages was coded using this category. 

NOTE: Exceptions to this rule: #1) When a call is ending, it was coded as “HH: End 

Task” if the driver looks at the phone and/or presses a button to end a call. #2) When a 

call is being answered, any glances or associated button presses were coded as “HH: 

Locate/Reach/Answer.” 

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 Appendix A.3 Operational Definitions 

NOTE: If the cell records indicate that the driver has received a text message, and the 

driver is seen checking then replying to this text message in the video, it was coded as 

follows: If the driver replies to the text message within 10 seconds after reading the text 

message, then the reply should be considered part of the same task, and was coded as 

“HH:Text” (the initial reading of the received text message should still be coded as 

“HH:View/Browse”). If the driver does NOT reply to the text message within 10 seconds 

and simply holds the phone (coded as “HH:Hold”) for 10+ seconds or puts the phone 

down (coded as “HH:End Task”), then the sent text should be considered a separate, nonsampled task and was NOT coded. 

o Event Start – For flip/slider phones, if the event is preceded by “HH: 

Locating/Reaching,” the event begins when the driver flips/slides open the phone 

OR first glances at the phone immediately before flipping it open in order to begin 

viewing/browsing/reading, whichever comes first. For non-flip phones, it begins 

when the first button on the keypad/touchscreen is depressed to begin 

viewing/browsing/reading OR when the driver first glances at the cell phone to 

begin viewing/reading, whichever comes first. If preceded by holding or talking, 

the event begins with the first glance to the phone prior to 

viewing/browsing/reading. 

o Event End –When the driver finished browsing/reading/viewing and begins 

moving to close the phone or put it down, OR moves onto another task with the 

phone (e.g., “HH: Holding”, “HH: Dialing”). Closing the phone, putting it 

down, or lowering it to a holding position should be coded as “HH: End Task.”

Hand-Held: Holding – When the driver holds a hand-held cell phone in his/her hand but does 

not interact with it. It does NOT count as holding if the phone is resting on the driver’s seat 

(next to or between legs), or on the driver’s lap (both of which would end the cell phone 

interaction and were coded as no cell phone task). 

NOTE (The 5-Second Rule): If the subject is viewing, dialing, or performing another 

task with a hand-held phone, then holds the phone without visually or manually 

interacting with it for at least 5 consecutive seconds, this “break” period was coded as 

“HH: Holding”, starting at the beginning of the 5-second time period. If the driver 

resumes another (or the same) subtask before the 5-consecutive-second period ends, it 

was not coded “HH: Holding.” Rather, we continued to code as the initial task until a 

new task begins. This is known as the “5-second rule” and is referred to frequently in 

these definitions. 

NOTE: Holding is assumed in all other hand-held subtasks (“HH:...”) and was not coded 

simultaneously with any other hand-held task. However, if the phone is being held 

during any PHF or IHF tasks, then “HH: Holding” was simultaneously coded. 

o Event Start –when other hand-held cell phone tasks (e.g., “HH: 

Reaching/Locating” or “HH: Talking/Listening”) have ended and driver continues 

to hold the phone in his/her hand(s) without further visual or manual interactions 

for at least 5 consecutive seconds. 

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 Appendix A.3 Operational Definitions 

o Event End –when the driver last touches the phone or when another hand-held 

cell phone task begins (e.g., “HH: Talking/Listening” or “HH: Dialing”).

Hand-Held: End Task- When the driver completes a specific cell phone objective by either 

pressing a button to end the call, putting the phone down after ending a call or text, or 

flipping/sliding the phone closed after ending a call or text.

o Event Start –when the driver (whichever comes first): 

1. First moves to press a button on a hand-held phone in order to end a call, 

OR first glances at the phone prior to pressing a button to end the call, 

2. OR for flip/slider phones, when the driver first moves to flip or slide the 

phone closed if no button is pressed to end the call, 

3. OR first moves to put the phone down or lower it to a holding position if 

no obvious button presses or phone manipulations to end the call/text 

occur 

4. OR the driver first glances at the phone to put it down or lower it to a 

holding position. 

o Event End – (whichever comes last): 

1. When the phone leaves the driver’s hand after ending the call/text, 

2. OR the driver last glances at the phone before moving on to a new task, 

3. OR another task begins (e.g., dialing a new number, or Holding for 5 or 

more seconds). 

Integrated Hands-Free: Press Button to Begin/Answer- When the driver presses a button on 

the steering wheel or center stack in order to begin a cell phone interaction. This can include 

pushing to answer a call, pushing to voice dial, or pushing to enter a voice command. 

o Event Start - when the driver begins to reach for the button on the steering wheel 

or center stack in order to answer/make a call, OR first glances toward the button 

on the steering wheel or center stack followed immediately by reaching for it, 

whichever comes first. If the driver adjusts radio or HVAC prior to initiating the 

cell phone task, then the first movement or glance toward the HVAC/radio should 

be coded as Event Begin. 

o Event End – when the driver’s hand moves away from the buttons on the steering 

wheel or center stack following the last button press/adjustment. 

Integrated Hands-Free: Talk/Listen/Voice Commands- When a driver talks, listens, or gives 

voice commands on an integrated device. Driver must be observed talking repeatedly with no 

obvious passenger interaction. Additionally, this option should only be used when the cell 

records indicate that the driver has made or received a call on an integrated hands-free device.

o Event Start - when the driver begins talking as if giving commands or having a 

conversation with no obvious passenger interaction, generally after pressing the 

button(s) on the steering wheel or center stack. 

Final Report 

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 Appendix A.3 Operational Definitions 

o Event End – when the driver stops talking repeatedly, often (but not always) 

followed by glancing and/or reaching for the button on the steering wheel or 

center stack in order to end the call. 

Integrated Hands-Free: Press Button to End Task- When the driver presses the button on the 

steering wheel or center stack in order to end the cell phone interaction. 

o Event Start - when driver begins to reach for the button on the steering wheel or 

center stack in order to end call, OR first glances toward the button on the steering 

wheel or center stack followed immediately by reaching for it to end a call, 

whichever comes first. 

o Event End – when the driver’s hand moves away from the button on the steering 

wheel or center stack following the button press OR the driver’s glance leaves the 

button location for the last time, whichever comes last. 

Portable Hands-Free: Locate/Put-on Headset/Earpiece- When the driver looks for or reaches 

towards a headset or earpiece. If more than one task occurs (i.e., driver looks for earpiece, 

reaches for it and then puts it in his ear), the first frame number would be the start of the first task 

(reaching for earpiece) and the last frame number coded would be the end of the last task (i.e., 

placing earpiece in ear.)

 Event Start - when the driver starts to move his/her hand in the direction of the 

headset/earpiece to retrieve it OR first glances as if looking for the 

headset/earpiece followed immediately by reaching for it, whichever comes first. 

 Event End - when the driver does one of the following (whichever comes last): 

1. For putting on a headset/earpiece, the last frame is when the driver 

finishes moving the earpiece into his/her ear and his/her hand begins to 

move away from the earpiece. 

2. For locating and reaching for the headset/earpiece, the event ends when 

one of the other categories begins (i.e., “HH: Dialing,” “PHF: 

Begin/Answer," “PHF: Talking/Listening,” “HH: Talking/Listening,” 

etc.). 

3. For locating the headset/earpiece and not picking it up, the last frame 

number coded would be the first frame number once the subject has 

shifted his/her gaze to something else (i.e., forward roadway) having 

glanced at the headset/earpiece for the last time.

Portable Hands-Free: Talk/Listen/Voice Commands- When a driver is talking on a headset, 

earpiece, or other aftermarket device, OR listening to a phone conversation, OR waiting for a 

person they are calling to pick up the phone. Driver must be observed talking repeatedly with no 

obvious passenger interaction to conclude that the headset/earpiece is in use. 

NOTE: This subtask should be coded if the talking subtask is performed on a portable 

hands-free device, even if the dialing, answering, or call ending subtask are performed 

using a hand-held phone.

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 Appendix A.3 Operational Definitions 

NOTE: If the driver uses the speaker phone function on a hand-held cell phone, code as 

“Hand-Held: Talk/Listen/Voice Commands” if the driver keeps the hand-held phone in 

his/her hand(s) while using the speaker phone function. Code as “Portable Hands-free: 

Talk/Listen/Voice Commands” if the driver puts the phone down (thus, does NOT hold it 

in his/her hand(s)) while using the speaker phone function. 

o Event Start - when the last button is pressed on the headset/earpiece before 

conversation begins. (i.e., when “PHF: Begin/Answer” has ended) 

o Event End - when the driver stops talking repeatedly, or first moves to press the 

button on the headset/earpiece in order to end the call (which would then be coded 

as “PHF: Press button to end”). 

Portable Hands-Free: Press Button to Begin/Answer - When the driver presses a button on 

the headset/earpiece in order to begin a cell phone interaction. This can include pushing to 

answer a call or pushing to give a voice command to make a call. This button may be located on 

the headset/earpiece itself, or occasionally somewhere on the wire connecting the device to the 

phone.

NOTE: If instead of pushing a button on the headset/earpiece to answer or make a call, 

the driver pushes a button or dials on a hand-held phone, this would be coded as “HH: 

Dialing” or “HH: Locate/Reach/Answer,” even if the subsequent conversation takes place 

via a Portable Hands Free device. 

o Event Start - when driver begins to reach for the button on the headset/earpiece, 

OR first glances toward the button on a wire connected to a headset/earpiece 

followed immediately by reaching for it, whichever comes first. If the driver 

adjusts radio or HVAC prior to initiating the cell phone task, then the first 

movement or glance toward the HVAC/radio should be coded as Event Begin. 

o Event End – when the driver’s hand moves away from the button on the 

headset/earpiece following the button press that initiates the interaction. 

Portable Hands-Free: Hold/Wear Headset/Earpiece- When a driver is holding a 

headset/earpiece in his/her hand or wearing it on his/her head but not interacting with it (and not 

involved in a phone conversation). Also code as “PHF: Hold/Wearing” if the driver has been 

holding the earpiece/headset in his/her hand(s) for some time and finally moves to put it on. It 

does NOT count as holding if the headset/earpiece is resting on the driver’s seat (next to or 

between legs), or on the driver’s lap.

NOTE: If the subject is talking/listening on a portable hands-free device or performing 

another task with a hand-held phone or portable hands-free device, then holds the 

headset/earpiece in hand or on his/her head without interacting for at least five 

consecutive seconds, this “break” period should be coded as “PHF: hold/wear 

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 Appendix A.3 Operational Definitions 

headset/earpiece.” If the driver resumes another task before the 5-consecutive-second 

period ends, do NOT code “PHF: Hold/Wear headset/earpiece.” 

NOTE: While coding PHF: Talk/Listen, do NOT intersperse PHF: Hold/Wear unless it 

is clear that a phone call has ended. The driver may stop talking for periods of time 

(including breaks longer than 5 seconds) to listen to the conversation. This should be 

coded straight through as PHF: Talk/Listen. 

NOTE: Holding/wearing headset or earpiece is assumed in all other Portable Hands-Free 

(“PHF:...”) subtasks and does not need to be coded simultaneously with any other PHF 

task. However, if a headset/earpiece is being held or worn during any HH or IHF tasks, 

then “PHF: Holding/Wearing” would need to be simultaneously coded. 

o Event Start –when other PHF cell phone tasks (e.g., reaching/locating or talking) 

have ended and driver continues to hold headset/earpiece in hand or on his/her 

head without further visual or manual PHF interactions. 

o Event End –when the driver moves to put the headset/earpiece down and last 

touches it OR when another cell phone task begins (e.g., talking/listening or 

dialing). 

Portable Hands-Free: Press Button to End- When the driver presses the button on the 

headset/ear piece in order to end the cell phone interaction. This button may be located on the 

headset/earpiece itself, or occasionally somewhere on the wire connecting the device to the 

phone.

NOTE: If instead of pushing a button on the headset/earpiece to end a call, the driver 

pushes a button on a hand-held phone, this would be coded as “HH: End Task,” even if 

the conversation took place via a Portable Hands-Free device. 

o Event Start - when driver begins to reach for the button on the 

headset/earpiece/wire, OR first glances toward the button on the 

headset/earpiece/wire followed immediately by reaching for it, whichever comes 

first. 

o Event End – when the driver’s hand moves away from the button on the 

headset/earpiece/wire following the button press that ends the call AND the driver 

has completed the last glance toward the button, whichever comes last. 

Cell Phone Navigation- When the driver is using the navigation feature of a hand-held cell 

phone. We do not entirely know what this will look like, but it may occur when the phone is in a 

cradle on the dash, or when the driver is clearly using the phone for turn-by-turn navigation 

purposes.

NOTE: Please note this interaction in the Comments section of Excel log so that a closer 

examination can be performed. 

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 Appendix A.3 Operational Definitions 

o Event Start –when the driver begins reaching for the cell phone, OR when the 

driver begins to look at the phone for purposes of navigation, whichever comes 

first. 

o Event End – when the driver reaches his/her destination, OR manually deactivates 

the navigation feature, whichever comes last. 

Other Cell Phone Tasks - When a driver is interacting with a hand-held cell phone, portable 

hands-free device, or integrated hands-free device in some manner not described in previous 

categories. This includes, but is not limited to, the following: 

1. When the driver plugs a hand-held phone into a power charger. 

2. When the subject is playing with a hand-held phone or portable hands-free device, or 

fiddling with them without any purposeful manipulation. 

3. When the subject puts a hand-held cell phone into a case after holding it in his/her 

hand for 5 or more consecutive seconds after other HH tasks have ended. Includes 

reaching for the separate case, maneuvering phone into the case, and then putting it 

down or holding it (coded as holding if longer than 5 seconds). 

NOTE: If subject must remove a hand-held cell phone from the case before using it, 

code as “HH: locating/reaching/answering.” If the subject is putting the phone back 

INTO case immediately following a call or text, code it as “HH: End Task.” If the 

subject is putting the phone back INTO a case after “HH: Holding,” code as “Other Cell 

Phone Task.” 

NOTE: Define the observed behaviors in the Comments section of Excel log. 

o Event Start –when other identifiable cell phone tasks have ended, OR if isolated 

from other tasks, the event begins when a cell phone task that does not fit into 

other categories begins.

o Event End - when subject puts hand-held phone or portable hands-free device 

down or begins another identifiable subtask (i.e., “HH: dialing,” “PHF: 

talking/listening,” etc.). 

Both Hands off Steering Wheel – Anytime the driver removes both hands from the steering 

wheel for a non-driving-related reason while the vehicle is in motion (speed >0). This does NOT 

have to be related to the cell phone task in order to be coded (e.g., it could be to adjust the radio), 

but DOES need to be non-driving related (i.e., crossing hands to turn steering wheel does not 

count). 

NOTE: Both hands off the wheel should ONLY be coded when the vehicle is in motion 

and the speed is greater than 0 as witnessed from the video. When the vehicle is 

stationary, both hands off the wheel can be ignored. 

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 Appendix A.3 Operational Definitions 

NOTE: If both hands are off the wheel for a driving-related reason, do NOT code. If 

one hand is off the wheel due to phone use, and the second hand is needed off the wheel 

for driving-related reasons (e.g., to shift gears), then this would be related to cell phone 

use and should be coded. If the driver is on a hands-free device and removes both hands 

from the wheel to gesture during conversation or perform other non-driving related tasks 

(e.g., eating and radio adjustments), then also code. When in doubt, code as Both Hands 

off Steering Wheel. 

o Event Start – when the driver first has no hands on the steering wheel 

o Event End – when the driver returns at least one hand to the steering wheel 

Recap of Special Scenarios 

1. Viewing While Answering a Hand-Held phone: At the beginning of a call, code as “HH: 

Reaching/Locating/Answering” straight through even if the driver looks at a hand-held 

phone or presses a button to answer a call. “HH: Locating/Reaching/Answering” has an 

implied “viewing” component, so it is not needed to call it out separately. If the driver 

has to open a flip phone, pull antenna up, or remove the phone from a case before 

answering a call, also code as “HH: locating/reaching/answering.” 

2. Cell Phone Cases: If subject must remove a hand-held cell phone from the case before 

using it, this should be included as “HH: Locating/Reaching/Answering.” But if subject 

is putting it back INTO case immediately after using it, include as “HH: End Task.” If 

subject puts phone back into case after a period of “HH: Holding,” then code it as Other 

Cell Task. 

3. Speaker Phone Talking: If the driver uses the speaker phone function on a hand-held cell 

phone to have a cell phone conversation: 

a. Code as “HH: Talk/Listen/Voice Commands” if the driver keeps the hand-held 

phone in his/her hand(s) while using the speaker phone function. 

b. Code as “PHF: Talk/Listen/Voice Commands” if the driver puts the phone down 

(thus, does NOT hold it in his/her hand(s)) while using the speaker phone 

function. 

4. Text Messages: If the cell records indicate that the driver has received a text message, 

and the driver is seen checking then replying to this text message in the video, code as 

follows: 

a. If the driver replies to the text message within 10 seconds after reading the text 

message, then the reply should be considered part of the same task, and should be 

coded as “HH: Text” (the initial reading of the received text message should still 

be coded as “HH: View/Browse”). 

b. If the driver does NOT reply to the text message within 10 seconds and simply 

holds the phone (coded as “HH: Hold”) for 10+ seconds or puts the phone down 

Final Report 

84 
 Appendix A.3 Operational Definitions 

(coded as “HH: End Task”), then the sent text should be considered a separate, 

non-sampled task and should NOT be coded. 

Final Report 

85 
 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

A.4 Driver, Vehicle, and Environmental Factors 

Coded for Cell Phone Subtasks 

The first two steps of the Cell Phone Pilot Analysis reduction work were (1) to identify the start 

and end points of sampled cell phone interactions while driving based on records of calls and text 

messages provided by the cell phone company via the study participants, and (2) within those 

interactions, code the duration of cell phone subtasks (e.g., reaching for phone, dialing, talking). 

This step in the reduction involved a close examination of those subtasks for a variety of vehicle, 

environmental, and driver-related factors. 

Separate events were created for each unique cell phone subtask associated with each sampled 

call and text message. A randomly selected 6-second clip of one talking, one holding a handheld 

phone, and one wearing a portable hands-free device (where applicable) were reduced for each 

interaction. All other subtasks and subtask combinations were reduced in their entirety. 

Page 1 of Question Annotation 

1. InteractionEventID (text): Interaction Event ID: Enter the INTERACTION Event ID 

from the reduction log. (This number will be used to tie this subtask back to the whole 

cell phone interaction.) 

2. Seatbelt: Driver seatbelt use at START of event: 

a. Yes, belt worn 

b. No, belt NOT worn 

c. Unable to determine 

3. HHPhoneType: Type of hand-held phone the driver uses for the majority of the 

event: 

a. NA Subtask Baseline Event (Skip to Page 2) 

b. No hand-held phone used (Skip to Page 2) 

c. Standard keys on front of phone 

d. Vertical flip-phone 

e. Horizontal flip-phone/Slide keyboard 

f. Touch screen 

g. BlackBerry/QWERTY on Front 

h. Unable to determine 

4. PhonePriorLocation: Location of hand-held phone prior to being reached for 

(Reaching subtasks only): applies only to “HH: Locate/Reach/Answer” subtasks 

a. Reaching for phone does not occur – choose this option if the subtask being coded 

is an HH task other than “HH: Locate/Reach/Answer” (such as, “HH: 

Talk/Listen,” “HH: Text,” etc.) 

b. Shirt/Jacket Pocket 

c. Pants Pocket 

d. Cup Holder 

e. On Dash (not in cradle) 

f. Purse (if seen) 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

g. Passenger Seat 

h. In Cradle – usually found attached to dash or windshield 

i. Glove Box 

j. Center Console Storage 

k. Other 

l. Unable to Determine 

m. No Hand-Held Phone Used 

n. N/A (Baseline) 

5. PhoneUseLocation: Location of hand-held phone during majority of event (not for 

reaching or ending subtasks): applies only to “HH: Dial,” “HH: View/Browse,” “HH: 

Talk/Listen,” “HH: Text,” and “HH: Hold” subtasks. 

a. N/A, Reaching or ending HH call – choose this option if the subtask being coded 

is “HH: Locate/Reach/Answer” or “HH: End Task.” 

b. In right hand against right ear 

c. In left hand against left ear 

d. In one hand on steering wheel (low) – 5:00-7:00 on a clock. 

e. In both hands resting on steering wheel (low) 

f. In one hand resting on steering wheel (middle) – 2:00-4:00 or 8:00-10:00 on a 

clock. 

g. In both hands resting on steering wheel (middle) 

h. In one hand resting on steering wheel (high) – 11:00-1:00 on a clock. 

i. In both hands resting on steering wheel (high) 

j. In one hand raised out in front of forward view 

k. In both hands raised out in front of forward window 

l. In one hand to side of/in front of steering wheel 

m. In both hands to side of/in front of steering wheel 

n. In one hand below steering wheel 

o. In both hands below steering wheel 

p. In one hand placed in front of mouth 

q. In both hands placed in front of mouth 

r. In right hand against left ear (cross body) 

s. In left hand against right ear (cross body) 

t. Not in hand – Other 

u. No hand-held phone used 

v. N/A (Baseline) 

Final Report 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

Final Report 

88 

Hand placement on steering wheel diagram 

Middle Middle 

High 

Low 

Page 2 of Question Annotation 

6. AmbientLighting: Ambient Lighting at the START of the event: 

a. Daylight 

b. Dusk – use if the ambient lighting is mostly dark and continues to darken 

throughout the file. Do not use if it the ambient lighting is daylight, but it is 

cloudy. 

c. Darkness, lighted – It is nighttime during the subtask, but the roadway is lighted 

d. Darkness, not lighted – It is nighttime during the subtask, and the roadway is 

NOT lighted 

e. Dawn – use if the ambient lighting is mostly dark and lightens throughout the file. 

Do not use if it the ambient lighting is daylight, but it is cloudy. 

f. Task is not Started Outside 

g. Unable to determine 

7. Weather: Weather conditions at the START of the event: 

a. No Adverse Conditions – includes cloudy/overcast skies with no visible falling 

precipitation 

b. Light Rain/Mist 

c. Heavy Rain 

d. Snowing/Sleeting 

e. Fog 

f. Rain + Fog 

g. Snow + Fog 

h. Smoke, dust - There is smoke and/or dust, either stagnant or blowing, in the air 

i. Other - There is some type of adverse atmospheric condition present, not 

described in other categories 

j. Unable to determine 

8. RoadSurface: Road surface condition at the START of the event: 

a. Dry - There is no foreign material (rain, snow, oil, etc.) on the roadway in the area 

of the event (nothing on the road to affect the driving task) 

b. Wet - Roadway is completely or partially wet in the area of the event (not snowy, 

icy, muddy, or oily) 
 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

c. Snowy - There is some amount of unmelted snow or slush on the roadway in the 

area of the event, enough to affect the driving task (no ice on the road in the area 

of interest) 

d. Icy - There is some amount of ice on the roadway in the area of the event, enough 

to affect the driving task 

e. Muddy - There is some amount of mud on the roadway in the area of the event, 

enough to affect the driving task 

f. Oily - There is some amount of oil, grease, or other slippery fluid on the roadway 

in the area of the event, enough to affect the driving task 

g. Other - There is some type of foreign substance on the road, not listed in previous 

categories, enough to affect the driving task 

h. Unable to determine 

9. StartStopped: Does the event START while the vehicle is stopped? 

a. No 

b. Yes, at intersection (either at signal or at stop sign, may be first in queue, or 

behind line of other queued vehicles) 

c. Yes, in traffic (does not include intersections. This is to be used for traffic jam 

situations.) 

d. Yes, parked (prior to driving, after parking, or waiting for passenger to get in) 

e. Yes, other (in line at drive-thru, etc.) 

f. Unable to determine 

10. AllStopped: Does the event occur ENTIRELY while the vehicle is stopped? 

a. No (Continue) 

b. Yes, at intersection (Continue) 

c. Yes, in traffic (Continue) 

d. Yes, parked (Stop and Save) 

e. Yes other (Continue) 

f. Unable to determine (Continue) 

Page 3 of Question Annotation 

11. TrafficFlow: Traffic Flow at the START of the event: Roadway design (including the 

presence or lack of a median) at the start of the event. If the event starts while the driver 

is at an intersection, the traffic flow conditions just prior to the intersection should be 

recorded.

a. Not divided, standard 2-way traffic way - with or without center line, but without 

center 2-way turn lane 

b. Not divided, with center 2-way turn lane 

c. Divided - median strip or barrier separates opposite direction 

d. One-way traffic 

e. No lanes – such as a Parking lot, Driveway, etc. 

f. Other 

g. Unable to determine 

Final Report 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

12. ContigTravelLanes: TOTAL number of CONTIGUOUS travel lanes present at 

START of the event, including turn, exit-entrance, and oncoming: includes the total 

number of all: lanes in the direction the driver is driving, oncoming lanes, turn lanes, 

entrance/exit ramps, and lanes with parked vehicles. If the event starts while the driver is 

at an intersection, the number of lanes just prior to the intersection should be recorded

a. 0 (No Lanes) - vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

b. 1 

c. 2 

d. 3 

e. 4 

f. 5 

g. 6 

h. 7 

i. 8+ 

j. Unable to determine 

13. NumDirectLanes: Number of travel through lanes in the DIRECTION OF TRAVEL 

ONLY at the START of the event: includes only the total number of lanes in the 

direction the driver is driving. Do NOT include: oncoming lanes, turn lanes, 

entrance/exit ramps, or lanes with parked vehicles. If the event starts while the driver is at 

an intersection, the number of lanes just prior to the intersection should be recorded 

a. 0 (No Lanes) – vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

b. 1 

c. 2 

d. 3 

e. 4 

f. 5 

g. 6 

h. 7 

i. 8+ 

j. Unable to determine 

14. StartingLane: In which of the lanes counted in the question Above is the driver 

traveling at the START of the event? - Note: Lanes should be counted from left to 

right

a. Not in through lane 

b. 0 (No Lanes) - vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

c. 1 (Left-most lane or only lane) 

d. 2 

e. 3 

f. 4 

g. 5 

h. 6 

Final Report 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

i. 7 

j. 8+ 

k. Unable to determine 

Page 4 of Question Annotation 

15. RoadAlignment: Roadway alignment at the START of the event: 

a. Straight – Road alignment is straight 

b. Curve Left – Road alignment is curved to the left 

c. Curve Right – Road alignment is curved to the right 

d. Unable to determine 

16. RoadGrade: Roadway grade at START of the event: 

a. Level 

b. Grade Up – profile of road is graded, and vehicle is going up a hill 

c. Hillcrest – vehicle is at a hillcrest (area of transition between an upgrade and a 

downgrade) 

d. Grade Down – profile of road is graded, and vehicle is going down a hill 

e. Dip – vehicle is in a dip 

f. Unable to determine 

Page 5 of Question Annotation 

17. Locality: Locality at the START of the event: 

a. Interstate/bypass/divided highway with no traffic signals 

b. Bypass/divided highway with traffic signals 

c. Business/industrial - Vehicle passes any type of business or industrial structure 

d. Open country - Other than the roadway, there is nothing visible that is described 

in any of the other categories 

e. Residential - Vehicle passes at least one house or evidence of a residential 

neighborhood but does not drive through a business or industrial area. 

f. Construction zone - Vehicle is in a construction zone (construction equipment, 

barrel, etc. are visible) (This category takes precedence over others)

g. School - Vehicle passes any type of school building, including adult learning 

institutions (This category takes precedence over others)

h. Church (This category takes precedence over others)

i. Playground - Vehicle passes any type of playground or children's playing field 

(This category takes precedence over others)

j. Other - Locality is one not described in other categories 

k. Unable to determine 

18. TrafficDensity: Traffic density at the START of the event: 

a. N/A – Stopped at Intersection 

b. LOS A1: Free flow – No leading traffic in any lane – Subject driver is unaffected 

in the traffic stream because there are no leading vehicles in any lane. Freedom to 

select desired speeds and to maneuver within the traffic stream is at the highest 

level possible. 

Final Report 

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Environmental Factors Coded 

c. LOS A2: Free flow – Leading traffic present in at least one lane - Individual 

drivers are virtually unaffected by the presence of others in the traffic stream. 

Freedom to select desired speeds and to maneuver within the traffic stream is 

extremely high. The general level of comfort and convenience provided to the 

motorist, passenger, or pedestrian is excellent. 

d. LOS B: Flow with some restrictions - In the range of stable flow, but the 

presence of other users in the traffic stream begins to be noticeable. Freedom to 

select desired speeds is relatively unaffected, but there is a slight decline in the 

freedom to maneuver within the traffic stream from LOS A. The level of comfort 

and convenience provided is somewhat less than at LOS A, because the presence 

of others in the traffic stream begins to affect individual behavior. 

e. LOS C: Stable flow, maneuverability and speed are more restricted - In the range 

of stable flow, but marks the beginning of the range of flow in which the 

operation of individual users becomes significantly affected by interactions with 

others in the traffic stream. The selection of speed is now affected by the 

presence of others, and maneuvering within the traffic stream requires substantial 

vigilance on the part of the user. The general level of comfort and convenience 

declines noticeably at this level. 

f. LOS D: Unstable flow - temporary restrictions substantially slow driver - Highdensity, but stable flow. Speed and freedom to maneuver are severely restricted, 

and the driver or pedestrian experiences a generally poor level of comfort and 

convenience. Small increases in traffic flow will generally cause operational 

problems at this level. 

g. LOS E: Flow is unstable, vehicles are unable to pass, temporary stoppages, etc. - 

Operating conditions at or near the capacity level. All speeds are reduced to a 

low, but relatively uniform value. Freedom to maneuver within the traffic stream 

is extremely difficult, and it is generally accomplished by forcing a vehicle or 

pedestrian to "give way" to accommodate such maneuvers. Comfort and 

convenience levels are extremely poor, and driver or pedestrian frustration is 

generally high. Operations at this level are usually unstable, because small 

increases in flow or minor perturbations within the traffic stream will cause 

breakdowns. 

h. LOS F: Forced traffic flow, low speeds, traffic volumes below capacity - Forced 

or breakdown flow. This condition exists wherever the amount of traffic 

approaching a point exceeds the amount which can traverse the point. Queues 

form behind such locations. Operations within the queue are characterized by 

stop-and-go waves, and they are extremely unstable. Vehicles may progress at 

reasonable speeds for several hundred feet or more, then be required to stop in a 

cyclic fashion. LOS F is used to describe the operating conditions within the 

queue, as well as the point of the breakdown. It should be noted, however, that in 

many cases operating conditions of vehicles or pedestrians discharged from the 

queue may be quite good. Nevertheless, it is the point at which arrival flow 

exceeds discharge flow, which causes the queue to form, and LOS F is an 

appropriate designation for such points. 

i. Unable to determine 

Final Report 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

19. LVPresent: Is there a lead vehicle traveling in the same lane at the START of the 

event? 

a. Yes 

b. No (Skip to Page 6) 

c. Unable to determine 

20. LVObjectID (text): What is the object ID of the lead vehicle reported by the radar at 

the START of the event? 

o If there is a lead vehicle reported by the radar, enter the Object ID 

o If radar data is not available, enter “N/A” 

o If unsure, enter “Unable to determine” 

21. LVActualRange (text): What is the X-Range to the lead vehicle reported by the 

radar at the START of the event? 

o If there is a lead vehicle reported by the radar, enter the X_Range 

o If radar data is not available, enter “N/A” 

o If unsure, enter “Unable to determine” 

22. LVEstRange: Estimate the range to the lead vehicle at the START of the event: 

a. Far (Greater than 40 m or 3 standard lane markings away) 

b. Medium (Between 12 and 40 m or 1-3 standard lane markings away) 

c. Close (Less than 12 m or 1 standard lane marking away) 

d. Unable to determine 

e. N/A (No lead vehicle) 

Lead Vehicle Range Estimate Diagrams 

***Standard lane markings are 10 ft. (3 m) long, and the distance between each one is 30 ft. (9 

m). Thus, from the start of one standard marking to the start of the next is 40 feet or about 12 

meters. Non-standard lane markings (such as during a merge or delineating a turn lane) have 

different measurements and cannot be used in this manner. 

Close (Less than 14 m on radar, or just over one standard lane marking) 

 

Final Report 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

Medium (14 to 40 m on radar or 1-3 standard lane markings) 

 

Far (Greater than 40 m on radar or more than 3 standard lane markings) 

 

Page 6 of Question Annotation 

23. LVActualRate (text): What is the relative X-velocity of the lead vehicle reported by 

the radar at the START of the event? 

o If there is a lead vehicle reported by the radar, enter the X-velocity 

o If radar data is not available, enter “N/A” 

o If unsure, Enter “Unable to determine” 

24. LVEstRate: Estimate the closing rate to the lead vehicle at the START of the event: 

a. Distance Rapidly Increasing 

b. Distance Increasing 

c. Distance Constant 

d. Distance Closing 

e. Distance Rapidly Closing 

f. Unable to Determine 

g. N/A (No lead vehicle) 

25. SVLaneChange: Does the subject driver CHOOSE to change lanes during the 10-

second time interval centered on the start of the baseline or subtask? This 10-second 

time interval includes 5 seconds before the start of the event to 5 seconds after the start of 

the event. 

Final Report 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

a. No - driver does not change lanes, OR any lane change performed is forced by 

lane closure, merging requirements, or turn lane movements 

b. Yes, planned lane change – driver changes lanes based on a choice to travel in a 

different lane. This does NOT include when the driver makes required merges 

(such as merging onto/off of a highway, moving into a turn lane, or lanes 

ending/beginning – all of which should be answered “No”). 

c. Yes, evasive/unplanned lane change – driver changes lanes in order to avoid an 

accident, or an animal/object/pedestrian in the forward roadway 

d. Unable to determine 

26. SVTurnSignal: If driver changes lanes as above, does he/she use the turn signal? 

a. Driver does not change lanes 

b. Yes 

c. No 

d. Unable to determine 

27. RVPresent: Is there a trailing rear vehicle traveling in the same lane as the driver at 

the START of the event? 

a. Yes 

b. No (Skip to Page (7) 

c. Unable to determine 

28. RVEstRange: Estimate the range to the rear vehicle at the START of the event: 

a. Far (Greater than 40 m or 3 standard lane markings away) 

b. Medium (Between 12 m and 40 m or 1 to 3 standard lane markings away) 

c. Close (Less than 12 m or 1 standard lane marking away) 

d. Unable to determine 

e. N/A (No rear vehicle) 

Rear Vehicle Range Estimate Diagrams 

***Standard lane markings are 10 ft. long, and the distance between each one is 30 ft. Thus, 

from the start of one standard marking to the start of the next is 40 feet or about 12 meters. Nonstandard lane markings (such as during a merge or delineating a turn lane) have different 

measurements and cannot be used in this manner. 

Final Report 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

Close (Less than14 m or just over one standard lane marking) 

 

 

Medium (14 to 40 m or 1-3 standard lane markings) 

Far (Greater than 40 m away or more than 3 standard lane markings) 

 

Page 7 of Question Annotation 

29. RVEstRate: Estimate the closing rate of the rear trailing vehicle at the START of the 

event: 

a. Distance Rapidly Increasing 

b. Distance Increasing 

c. Distance Constant 

d. Distance Closing 

e. Distance Rapidly Closing 

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 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

f. Unable to Determine 

g. N/A (No rear vehicle) 

30. RVLaneChange: Does the rear trailing vehicle change lanes to pass the subject 

vehicle within 10 seconds of the START of the event? This 10-second time interval 

includes the start of the subtask to 10 seconds after the start of the subtask. 

a. Yes, Rear Vehicle Moves to Pass (PLANNED) – Rear vehicle changes lanes 

based on a choice to travel in a different lane or in order to drive at a faster speed 

than the subject. This does NOT include when the rear vehicle makes required 

merges (such as merging onto/off of a highway, moving into a turn lane, or lanes 

ending/beginning – all of which should be answered “No”). 

b. Yes, Rear Vehicle Moves to Pass (EVASIVE) - rear vehicle changes lanes in 

order to avoid an accident, or an animal/object/pedestrian 

c. No – rear vehicle does not change lanes, OR any lane change performed is forced 

by lane closure, merging requirements, or turn lane movements 

d. Unable to determine 

e. N/A (No rear vehicle) 

31. RelationToJunction: Relation to junction at START of event: 

a. Non-junction – Subject vehicle is not close to a junction (the area formed by the 

connection of two roadways) 

b. Intersection – Subject vehicle is at or within 1 car length (~20 feet) of an 

intersection (roads cross at the same grade) 

c. Intersection-related – Subject vehicle is within 3 car lengths (~60 feet) of an 

intersection (where roads cross at the same grade), either approaching or exiting 

the intersection 

d. Interchange area – Subject vehicle is within the boundaries of an interchange with 

exit and/or entrance ramps present (a road junction that typically utilizes grade 

separation and one or more ramps to permit traffic on at least one road to pass 

through the junction without crossing any other traffic stream) 

e. Entrance ramp – Subject vehicle is on or entering/exiting an entrance ramp (a 

transition roadway connecting two roadways or used for entering through-traffic 

lanes) 

f. Exit ramp – Subject vehicle is on or entering/exiting an exit ramp (a transition 

roadway connecting two roadways or used for exiting through-traffic lanes) 

g. Driveway, alley access, etc. – Subject vehicle is on or entering/exiting a driveway, 

alley, or some other roadway providing access to property adjacent to the traffic 

way 

h. Rail grade crossing – Subject vehicle is close to the at-grade connection of a 

railroad bed and roadway 

i. Parking lot – subject vehicle is within the boundaries of a parking lot 

j. Other – subject vehicle is related to a junction in a manner not described in other 

categories. This includes tunnels, toll booths, and bridges 

k. Unable to determine 

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 Appendix A.4 Driver, Vehicle, and 

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32. TrafficControlDevice: Traffic control device (if any) in effect at the START of the 

event: 

a. No traffic control - There is no traffic control applicable to the subject vehicle at 

the time of the event 

b. Traffic signal - A traffic signal (by colors or flashing) is controlling some aspect 

of the traffic flow applicable to the subject vehicle 

c. Stop sign 

d. Yield sign 

e. Construction signs/warnings 

f. Slow or warning sign, other 

g. School-zone related sign 

h. Officer or watchman/traffic guard 

i. Traffic lanes marked - There are markings on the road that contain information or 

warnings applicable to the driving task for the subject vehicle (use if NO other 

types of devices/signs are used to convey the same information). Does not 

include Railroad crossings (see below). 

j. No passing signs 

k. One-way road or street 

l. Railroad crossing with markings or signs - A railroad crossing with associated 

signage (including markings on the road, signs, cross bucks) is controlling some 

aspect of traffic flow applicable to the subject vehicle 

m. Railroad crossing with signals - A railroad crossing with associated signals 

(including flashing lights, traffic lights) is controlling some aspect of traffic flow 

applicable to the subject vehicle 

n. Railroad crossing with gate and signals - A railroad crossing with associated 

gate(s) with or without signals (including flashing lights, traffic lights). Is 

controlling some aspect of traffic flow applicable to the subject vehicle 

o. Other - There is some type of traffic control device, not described in previous 

categories, controlling some aspect of traffic flow applicable to the subject vehicle 

p. Unable to determine 

Page 8 of Question Annotation 

33. IntersectionPresent: What is the first type of intersection entered within 10 seconds 

from START of the event? This 10-second time interval includes the start of the 

subtask to 10 seconds after the start of the subtask. 

a. No Intersection Entered – Skip to Page 9 – if this option is selected, SKIP to 

question 36 on page 9 of the question annotation 

b. Signalized – subject’s path through intersection is controlled by a stoplight only 

c. Stop sign – subject’s path through intersection is controlled by a stop sign only 

d. Yield sign – subject’s path through intersection is controlled by a yield sign only 

e. Uncontrolled – subject’s path through intersection is not controlled by any means 

(no signs nor stoplights) 

f. Unable to determine 

34. IntersectionScan1: For the intersection coded above, does the driver appropriately 

scan for traffic PRIOR to entering the intersection? Proper scanning consists of 

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gazing to roadway junctions and NOT driveways, alleyways, or parking lot entrances. 

For a 4-way intersection, a glance to the left and right is required; for a right 3-way 

intersection, a glance to the right is required; for a left 3-way intersection, a glance to the 

left is required, etc. These glances are required regardless of traffic control status (traffic 

light color, etc.). 

a. Yes, driver scans appropriately 

b. No, driver does not scan 

c. Unable to determine 

d. N/A - No intersection entered 

35. IntersectionViolate: What stopping behavior is exhibited at the intersection coded 

above? (use the unit converter to convert to miles per hour)

a. Stop not required 

b. Proper stop performed 

c. Rolling stop (minimum speed <15 mph, but greater than 0) 

d. Complete stop, but past the stop bar/sign AND in path of cross traffic 

e. No stop when stop required (minimum speed is >=15mph) 

f. Unable to determine 

g. N/A - No intersection entered 

36. IntersectionScan2: If the driver stops as first in queue at a light at the intersection 

coded above, does he/she scan within 6 seconds before the vehicle starts moving? 

Proper scanning consists of gazing to roadway junctions and NOT driveways, alleyways, 

or parking lot entrances. For a 4-way intersection, a glance to the left and right is 

required; for a right 3-way intersection, a glance to the right is required; for a left 3-way 

intersection, a glance to the left is required, etc. These glances are required regardless of 

traffic control status (traffic light color, etc.).

a. N/A, driver does not stop 

b. N/A, driver stops, but not first in queue at light 

c. Yes, driver scans before moving 

d. No, driver does not scan before moving 

e. Unable to determine 

f. N/A - No intersection entered 

Page 9 of Question Annotation 

37. NumLaneBust (text): Number of unintentional lane busts occurring during this event 

– enter the total number of unintentional lane busts that occur during the entire event. Do 

NOT count intentional lane busts (such as when the driver must swerve to avoid an 

accident or an animal/object/pedestrian in the road, etc.). If there are no unintentional 

lane busts, enter “0” and skip to Page 10. 

38. BeginLaneBust1 (text): Begin timestamp of FIRST lane bust – enter the timestamp of 

the beginning of the first lane that occurs during this event. 

39. BeginLaneBust2 (text): Begin timestamp of SECOND lane bust – enter the timestamp 

of the beginning of the second lane that occurs during this event. 

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Final Report 

100 

 

40. BeginLaneBust3 (text): Begin timestamp of THIRD lane bust – enter the timestamp of 

the beginning of the first third bust that occurs during this event. 

Page 10 of Question Annotation 

41. SecondaryTask1: Secondary Task 1 – Indicate any secondary tasks (up to (3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

42. SecondaryTask2: Secondary Task 2 – Indicate any secondary tasks (up to (3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

43. SecondaryTask3: Secondary Task 3 – Indicate any secondary tasks (up to (3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

44. SecondaryTaskDesc (textbox): Define/Describe OTHER tasks above – For any 

secondary tasks listed as “other,” “unknown,” “other device,” “reaching for object: 

other,” or “holding object: other” above, provide a description. Also use this space to 

further explain anything unusual about the list distractions.

Secondary Task Description 

No Secondary Task There are no observable signs of driver distraction 

Cell Phone: 

Holding/Wearing 

ONLY (Does not 

Apply to Subtask 

Events) 

Driver is holding a hand-held phone without interacting with it 

in ANY way (including not talking on speaker phone) and/or 

Driver is wearing or holding an earpiece/headset without 

interacting with it in ANY way (including talking on it). Do 

NOT use this option if Driver is interacting with any phone, 

headset, or integrated device. See Cell Phone: Complex Task. 

Cell Phone: Complex 

Task (Does not 

Apply to Subtask 

Events) 

Driver is interacting with a hand-held phone, earpiece/headset, 

or integrated hands-free device in some way OTHER than 

simply holding/wearing it. This category includes 

reaching/locating, dialing (buttons or voice), talking, text 

messaging, browsing, viewing, or any other task beyond 

holding/wearing. 

Lost in thought 

Driver performs multiple non-specific eye glances within 6-

second period of time (not focusing on objects of glances), or 

appears to be in a daze resulting in potential conflict. 

Looked but did not see 

Driver is looking right at (or looks at) where incident occurs, but 

shows no reaction. Often seen when blind spot is checked, but 

vehicles present are not seen. 
 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

Final Report 

101 

Secondary Task Description 

Talking/singing/dancing 

(w/o passenger or 

cell) 

Driver is moving lips as if in conversation or singing a song. 

Also use if driver is moving his/her arms, head, or other body 

part in time with the beat of music 

Mark this if driver is talking or singing or dancing and there is 

no obvious passenger component (either passenger is clearly not 

present or the driver is not looking in the direction of a 

passenger seat and does not turn head as if communicating with 

someone). 

Reading/Writing 

Driver is reading or writing on material that is in the vehicle, but 

not a part of the vehicle (i.e., not reading external signs, or radio 

display). 

This could be reading or writing on directions, paper material, 

packaging. If reading a phone number, record as dialing cell 

phone. 

Cognitive, other 

Driver is emotionally upset or angry, or engaged in another 

activity not included in other categories, that requires the driver 

to obviously be thinking about something other than driving. 

Details about condition or emotional state should be specified in 

the appropriate questions. 

Interacting with 

passenger 

A passenger is visible or not visible, but the driver is clearly 

interacting with a passenger in either the adjacent or rear seat. 

This could be talking, listening, reacting to (i.e., laughing), 

moving toward or away from the passenger (i.e., reaching for 

the passenger, or avoiding a pat from the person). 

Moving object in 

vehicle 

An object inside the vehicle is in motion and causes the driver to 

look away from the driving task, either due to the motion of the 

vehicle or due to another passenger throwing the object. (Ex. 

object fell off seat when driver stopped hard at a traffic light.) 

Insect in vehicle 

Interaction with any insect in the vehicle (e.g., swatting at 

insect, moving body to avoid insect, looking around trying to 

locate insect). 

Pet in vehicle 

Any interaction with pet, including petting, talking to, or 

moving pet or interacting with pet carrier. 

Only code if animal/pet is visible at some point in the trip file or 

if there is history/context with the driver and the driver is 

exhibiting behaviors that are appropriate to having a pet in the 

vehicle. 

Object dropped by 

driver 

Driver is holding something and it drops and the driver then 

picks it back up. 

This category supersedes other "reaching" categories in the 

situation of an object being dropped and immediately retrieved. 

Reaching for object, 

other 

Driver reaches for an object not described in any other category. 

Once the driver has finished reaching for the object and has it in 

hand (if not being moved for intended usage), then it becomes 

"object in vehicle, other," as long as it doesn't fit into any of the 

other categories (e.g., eating, drinking, etc.). 
 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

Final Report 

102 

Secondary Task Description 

Holding object, other 

Driver is holding an object not described in other categories. 

Could be food, drink, pen, paper, etc. Must continue for at least 

5 seconds without other manipulations. If less than 5 seconds, 

code as previous task (e.g., reaching for object, personal 

hygiene). 

Object in vehicle, other 

Driver clearly is looking at, handling, or manipulating an object 

(visible or not) or thing located in the vehicle, other than those 

listed in other categories. 

Operating other 

electronic device 

Driver is manipulating some non-manufacturer-installed 

electronic device (PDA, laptop, mp3 player, etc.) either by 

pressing buttons, viewing, opening/closing, plugging in, etc. 

Reaching for this object should be coded as "Reaching for 

object, other." 

Adjusting radio or 

HVAC 

Driver interacts with climate control or radio either by touching 

the buttons on the center stack, dashboard, or steering wheel, or 

glancing at the controls. Includes inserting/retrieving CDs and 

adjusting vents. 

Adjusting/monitoring 

other devices 

integral to vehicle 

Driver interacts with a manufacturer-installed device other than 

those listed in other categories, either by touching or glancing at 

the device. 

Includes interaction with seat belt, door locks, sun visor, etc. 

Does NOT include interacting with driving-critical tasks such as 

turn signal, headlights, gear shift, and windshield wipers. 

Looking at non-driving 

related external 

object/event 

Driver is looking outside of the vehicle in the direction of what 

is obviously an object or incident that is not related to the 

driving task. May include looking at an accident, aspects of 

construction sites/zones, animals/pedestrians that are not in or 

entering the path of travel. 

Only mark if it is clear that the driver is tracking a specific 

external distraction as they drive by. Other non-specific or 

driving-related glances should be coded as "Driving related 

inattention to forward roadway" 

Eating/drinking 

Driver has food or drink that will be put in his/her mouth with or 

without the use of a utensil. If driver is chewing (except gum) 

also code as Eating/drinking. If driver is simply holding food or 

drink for 5 or more seconds, code as Holding Object: Other 

Smoking/tobacco 

Lighting, smoking, or extinguishing cigar or cigarette. Also 

includes use of chewing tobacco or holding a lit cigarette. 

Reaching for tobacco products should be coded "Reaching for 

object: other" 

Personal hygiene 

Includes applying make-up (including lotion/chapstick), 

checking self in mirror, purposefully fixing/brushing hair, 

shaving, tweezing, brushing/flossing teeth, putting 

on/removing/adjusting jewelry (including watches), putting 

on/removing/adjusting contacts or glasses. Reaching for 

hygiene-related items should be coded as "Reaching for object: 

other.” 

Does not include swiping hair from eyes or quick/thoughtless 

rubbing/scratching, twirling hair. 
 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

Final Report 

103 

Secondary Task Description 

Driving-related 

inattention to 

forward roadway 

Driver glances away from the direction of travel out a window 

or at a side or center mirror for a driving-related issue (i.e., 

changing lanes, crossing through an intersection). Exception: 

if the vehicle is backing and the driver is looking out of the left 

window to see the road in the direction of travel, this is not 

coded as a distraction. 

Other Secondary Task 

(define in Text 

box) 

Driver is looking in a location other than the direction of travel, 

in a manner not listed in other categories. 

Unknown 

Can't tell or make a judgment whether there is a distraction 

Ex. Part of the video is missing or there is insufficient 

information in the video to make a determination. 

Page 11 of Question Annotation 

45. DriverExpectation: If an external incident occurs within 6 seconds after the START 

of the event, describe the driver’s reaction to it: An external incident is anything 

unexpected or out of the ordinary that presents a safety hazard.

a. No external event occurs – if this option is selected, SKIP to question 44 at the 

bottom of this page on the question annotation 

b. Fully expects, drives appropriately/reacts in a timely manner 

c. Somewhat caught off guard, but quickly reacts in appropriate manner 

d. Very much caught off guard, has a delayed reaction (~ > 0.75 s) 

e. Extremely caught off guard, does not react at all 

f. Unable to determine 

46. Emotion: Prior to any external incident noted above, rate the driver’s emotional 

state during the first 6 seconds from the START of the event: 

a. Neutral/No Emotion Shown 

b. Happy 

c. Angry/Frustrated/Impatient 

d. Sad 

e. Surprised 

f. Other (Could be Concerned/Opinionated/Apologetic/Guilt/Contempt) 

g. Unable to determine 

Driver Emotional State Definitions 

Emotion Operational Definition 

Unable to Determine  Cannot tell what emotion the driver is showing 

Neutral/No Emotion 

Shown 

 The driver has a straight face, does not smile or laugh, does not 

gesture 

Happy  The driver smiles or laughs 

 The driver gestures in excitement 

Angry/Frustrated  The driver lowers/squeezes eyebrows, wrinkling forehead 

 The driver clenches his/her teeth 
 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

Final Report 

104 

Emotion Operational Definition 

 The driver yells (opens mouth wide with eyebrows lowered) 

 The driver gestures in anger/frustration 

 The driver raises his/her upper lip or tightens lips 

Sad 

 The driver has droopy eyebrows (raises inner eyebrows, lowers 

outer eyebrows) 

 The driver frowns by lowering the outer corners of his/her lips 

Surprised 

 The driver’s eyebrows raise 

 The driver’s mouth opens 

 The driver gestures 

Other  Emotional reaction that does not fit into any other category 

47. EmotionIntensity: Prior to any external incident noted above, rate the intensity of the 

driver’s emotional state during the first 6 seconds of the event: 

a. Neutral/No Emotion Shown 

b. Slight (Emotion Somewhat Shown) 

c. Marked or Pronounced (Emotion Very Much Shown) 

d. Severe (Emotion Extremely Shown) 

e. Unable to determine 

Driver Emotional Intensity Reduction Definitions 

Intensity of Emotion Operational Definition 

Unable to Determine  Cannot tell the intensity of the emotion 

Neutral/No Emotion Shown 

 The driver has a straight face, does not smile or laugh, 

does not gesture 

 Note, will always be selected if Neutral/No Emotion is 

selected above 

Slight (Emotion Somewhat 

Shown) 

 The driver no longer has a straight face 

 However, no gesturing or head movement is observed 

Marked or Pronounced 

(Emotion Very Much 

Shown) 

 The driver no longer has a straight face 

 The driver gestures one time in a reserved manner 

 The driver moves his head one time 

Severe (Emotion Extremely 

Shown) 

 The driver has wide eyes and a wide open mouth 

 The driver is screaming 

 The driver gestures wildly, or the driver moves his head 

frequently 

48. RaterSurprise As the analyst, how surprised/shocked/interested were you by the 

video captured during this event? 

a. No heightened level of surprise/shock/interest 

b. Somewhat surprised/shocked/interested 

c. Very much surprised/shocked/interested 

d. Extremely surprised/shocked/interested 

e. Unable to determine 
 Appendix A.4 Driver, Vehicle, and 

Environmental Factors Coded 

49. NoteComments (text): General Notes/Comments – include descriptions of any instances 

where you coded “Unable to determine” or “Other” in the questions above. As well as 

notes about any other circumstances that help to explain your responses and/or better 

define the conditions and occurrences of this event. Other notes you should type in 

include (but are not limited to) when the driver gets out of the vehicle during an event 

and particularly extreme weather conditions.

Final Report 

105 
 Appendix A.5 Definition of Eyeglance Locations 

Final Report 

106 

A.5 Definition of Eyeglance Locations 

Reductionists recorded the drivers’ eye glance locations over the duration of each sampled 

subtask. Eye glance locations were recorded at 10 Hz. The eyeglance locations, with definitions, 

are listed in Table 37. 

Table 37. Definitions of Eyeglance Locations From Reduction Protocol 

Keyboard 

Shortcut Glance Location Operational Definition 

F Forward (Center) 

Any glance out the forward windshield directed towards the 

direction of the vehicle’s travel. Note that when the vehicle is 

turning, these glances may not be directed directly forward but 

towards the vehicle’s heading. Count these as forward glances. 

D Left Forward 

Any glance out the forward windshield where the driver appears to 

be looking specifically out the left margin of the windshield (e.g., as 

if scanning for traffic before turning or glancing at oncoming 

traffic). This glance location includes anytime the driver is looking 

out the windshield, but clearly not in the direction of travel (e.g., at 

road signs or buildings). 

G Right Forward 

Any glance out the forward windshield where the driver appears to 

be looking specifically out the right side of the windshield (e.g., as 

if scanning for traffic before turning, at a vehicle ahead in an 

adjacent lane, or reading a road sign). 

This is often preceded or followed by Left Forward. This glance 

location includes anytime the driver is looking out the windshield, 

but clearly not in the direction of travel (e.g., at road signs or 

buildings). 

M Rearview Mirror 

Any glance to the rearview mirror or equipment located around it. 

This glance generally involves movement of the eyes to the right 

and up to the mirror. 

This includes glances that may be made to the rearview mirror in 

order to look at or interact with back seat passengers. 

L Left Window/Mirror Any glance to the left side mirror or window. 

R Right Window/Mirror Any glance to the right side mirror or window 

S Over-The-Shoulder 

(left or right) 

Any glance over either of the participant’s shoulders. In general, 

this will require the eyes to pass the B-pillar. If over the left 

shoulder, the eyes may not be visible, but this glance location can be 

inferred from context. 

NOTE: If it is clear from context that an over-the-shoulder glance is 

being made NOT to check a blind spot but instead to interact with a 

rear seat passenger (e.g., food/toy is being handed back), then code 

the glance as Passenger. If context cannot be known with a high 

level of certainty, then code as Over-the-Shoulder. 

I Instrument Cluster 

Any glance to the instrument cluster underneath the dashboard. This 

includes glances to the speedometer, control stalks, and steering 

wheel. 

C Center Stack Any glance to the vehicle’s center stack (vertical). 
 Appendix A.5 Definition of Eyeglance Locations 

Final Report 

107 

Keyboard 

Shortcut Glance Location Operational Definition 

Not to be confused with center console (cup holder area between 

driver and passenger), which is discussed under “Interior Object.” 

P 

Cell Phone (electronic 

communications 

device) 

Any glance at a cell phone or other electronic communications 

device (e.g., BlackBerry), no matter where it is located. This 

includes glances to cell-phone-related equipment (e.g., battery 

chargers). 

H iPod (or similar) Any glance at an iPod or other personal digital music device, no 

matter where it is located 

W Interior Object 

Any glance to an identifiable object in the vehicle other than a cell 

phone. These objects include personal items brought in by the 

participant (e.g., purse, food, papers), any part of their body that 

may look at (e.g., hand, ends of hair), electronic devices other than 

cell phones (e.g., laptop, PDA), and also OEM-installed devices that 

don’t fall into other categories (e.g., door lock, window and seat 

controls). 

Glances to the center console (cupholder area between passenger 

seat and driver seat) will also be included in this category. 

The object does not need to be in the camera view for a specific 

frame to be coded with this category. If it is clear from surrounding 

video that the participant is looking at the object, this category may 

be used. This category can be used regardless of whether the 

participant’s hands are/aren’t visible. 

NOTE: If the driver is looking at something that the passenger is 

handing to the driver, code the eyeglance as Passenger, until the 

object is fully in the driver’s hand, then code as Interior Object 

(unless it’s a cell phone, code as Cell Phone). Also, if the driver is 

looking at something that the passenger is holding (but never hands 

to the driver), code as passenger glance (not interior object). 

A Passenger 

Any glance to a passenger, whether in front seat or rear seat of 

vehicle. You will need to use context (e.g., they’re talking, or 

handing something) in order to determine this in some situations. 

NOTE: This does NOT include glances made to rear seat passenger 

via the rearview mirror. Such glances should be coded as Rearview 

Mirror. 

NOTE: If the driver is looking at something that the passenger is 

handing to the driver, code the eyeglance as Passenger, until the 

object is fully in the driver’s hand, then code as Interior Object 

(unless it’s a cell phone, code as Cell Phone). Also, if the driver is 

looking at something that the passenger is holding (but never hands 

to the driver), code as passenger glance (not interior object). 

V No Video 

Unable to complete glance analysis because the face video view is 

temporarily unavailable. 

NOTE: this sometimes occurs for 1-2 timestamps at a time, and a 

“video not available” message may appear. If the glance location is 

the same before and after this occurs and the period is only 1-2 
 Appendix A.5 Definition of Eyeglance Locations 

Final Report 

108 

Keyboard 

Shortcut Glance Location Operational Definition 

timestamps long, then code through this period as the glance 

location present before and after. If the “video not available” period 

is longer than 2 timestamps OR it occurs during a transition 

between glance locations, use the “No Video” option. 

E 

No Eyes VisibleGlance Location 

Unknown 

Unable to complete glance analysis due to an inability to see the 

driver’s eyes/face. Video data is present, but the driver’s eyes and 

face are not visible due to an obstruction (e.g., visor, hand), or due 

to glare. 

Use this category when there is no way to tell whether the 

participant’s eyes are on or off the road. This is the default and most 

often used “unknown” option, but there may be times when the “off 

road” option listed below may be appropriate. 

T No Eyes Visible. Eyes 

Are Off-Road 

Unable to enter in specific glance location due to an inability to see 

the driver’s eyes/face. However, it is clear that the participant is not 

looking at the roadway. Video is present, but the driver’s eyes and 

face are not visible due to an obstruction (e.g. visor, hand), head 

position, or due to glare. 

Use this category when the eyes are not visible, you are not sure 

what the participant is looking at, but it is obvious that the eyes are 

not on the roadway. 

Z Eyes Closed 

Any time that BOTH the participant’s eyes are closed outside of 

normal blinking (e.g., the subject is falling asleep or rubbing eyes). 

As a rule of thumb, if the eyes are closed for five or more syncs (1/2 

a second) during a slow blink, code it as Eyes Closed. Otherwise, 

code it as the glance location present before the eyes closed. 

If one eye remains open, code the location according to the open 

eye. If only one eye is visible, code according to the visible eye. 

O Other 

Any glance that cannot be categorized using the above codes. Some 

pre-approved uses of the 

“other” option are listed below: 

 When the driver is looking forward, and then looks straight up at 

the sky as if watching a plane fly by. 

 When the driver is tilting head back to drink and the eyes leave 

the forward glance but do not really focus on anything at all. 
 Appendix A.6 Subtask-level Kinematic Data 

Final Report 

109 

A.6 Subtask-level Kinematic Data 

Kinematic measures were collected at different points along each subtask of interest. The 

following tables summarize when each variable was collected, expressed as a function of the 

general use for that variable. 

Table 38. Descriptive Kinematic Measures 

Variable SCE Interval SCE-Baseline 

Interval Subtask Interval 

Subtask-Baseline 

Interval 

Average Speed Entire sample Entire sample Entire subtask Entire subtask 

Minimum Speed Entire sample Entire sample Entire subtask Entire subtask 

Maximum Speed Entire sample Entire sample Entire subtask Entire subtask 
 Appendix A.6 Sub

Final Report 

110 

Table 39. Driving Performance Degradation Measures 

Variable SCE Interval SCE-Baseline Interval Subtask Interval Subta

Average Speed 20 s (-15s to +5s, centered on start of sample) 20 s (20 s beginning from start of sample) 20 s (20 s beginning from start of sample) 20 s (2

start of 

Average Speed 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (1

start of 

Minimum Speed 20 s (-15s to +5s, centered on start of sample) 20 s (20 s beginning from start of sample) 20 s (20 s beginning from start of sample) 20 s (2

start of 

Minimum Speed 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (1

start of 

Maximum Speed 20 s (-15s to +5s, centered on start of sample) 20 s (20 s beginning from start of sample) 20 s (20 s beginning from start of sample) 20 s (2

start of 

Maximum Speed 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (1

start of 

Speed Variance 20 s (-15s to +5s, centered on start of sample) 20 s (20 s beginning from start of sample) 20 s (20 s beginning from start of sample) 20 s (2

start of 

Speed Variance 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (1

start of 

Headway Variance 20 s (-15s to +5s, centered on start of sample) 20 s (20 s beginning from start of sample) 20 s (20 s beginning from start of sample) 20 s (2

start of 

Headway Variance 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (1

start of 

Peak Deceleration 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (10 s beginning from start of sample) 10 s (1

start of 

If the SV changes lanes, does the driver use the turn signal? 

10 s (± 5s centered on start of sample) 

10 s (± 5s centered on start of sample) 

10 s (± 5s centered on start of sample) 

10 s (± sample
 Appendix A.6 Subtask-level Kinematic Data 

Final Report 

111 

Table 40. Driver Adaptation Measures 

Variable SCE Interval SCE-Baseline 

Interval 

Subtask 

Interval 

SubtaskBaseline 

Interval 

Speed 

Start of sample 

6 s prior to the start 

of the sample 

Start of sample 

6 s prior to the 

start of the 

sample 

Start of subtask 

6 s prior to the 

start of the 

subtask 

Start of subtask 

6 s prior to the 

start of the 

subtask 

Range to LV Start of sample Start of sample Start of subtask Start of subtask 

Range Rate to LV Start of sample Start of sample Start of subtask Start of subtask 

Following Headway Start of sample Start of sample Start of subtask Start of subtask 

TTC Start of sample Start of sample Start of subtask Start of subtask 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

A.7 Driver, Vehicle, and Environmental Questions for 

Safety-Critical Events 

Safety-critical events (SCEs) were identified by first identifying through an automated script 

possible hard braking, hard steering, and close time-to-collision events using the kinematic data 

that exists in the Cell Phone Pilot database. Then, reductionists reviewed the video for these 

potential events and validated the events that were true safety-critical events. Some additional 

events were identified by analysts as video was reviewed during other reduction tasks. All valid 

events were then confirmed by an expert, and the first phase of reduction (conflict description) 

was completed at that point. The start and end timestamps for each event were updated based on 

the conflict information so that each event is now 6 seconds long, with the precipitating (or 

causative) event occurring after 5 seconds. This protocol provides instructions on how to 

complete the reduction for environmental and driver-related factors surrounding these events. 

Note that the window for analysis (6 seconds) includes 5 seconds of driving before the event 

begins, and continues for 1 second after the event begins. For this reason, the safety-critical 

situation is not always completely resolved at the end of the 6 seconds, but the time period of 

interest for the analysis is limited to the 6 seconds. 

Page 1 of Question Annotation 

4. Seatbelt: Driver seatbelt use at Precipitating Event: 

a. Yes, belt worn 

b. No, belt NOT worn 

c. Unable to determine 

5. HHPhoneType: Type of hand-held phone the driver uses for the majority of the 

event: 

a. No hand-held phone used (Skip to Page 2) 

b. Standard keys on front of phone 

c. Vertical flip-phone 

d. Horizontal flip-phone/slide keyboard 

e. Touch screen 

f. BlackBerry/QWERTY on front 

g. Unable to determine 

6. PhonePriorLocation: Location of hand-held phone prior to being reached for 

(Reaching subtasks only): applies only to “HH: Locate/Reach/Answer” subtasks 

o. No hand-held phone used 

p. Reaching for phone does not occur – choose this option if the subtask being coded 

is an HH task other than “HH: Locate/Reach/Answer” (such as, “HH: 

Talk/Listen,” “HH: Text,” etc.) 

q. Shirt/Jacket Pocket 

r. Pants Pocket 

s. Cup Holder 

t. on Dash (not in cradle) 

u. Purse (if seen) 

Final Report 

112 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

v. Passenger Seat 

w. In Cradle – usually found attached to dash or windshield 

x. Glove Box 

y. Center Console Storage 

z. Other 

aa. Unable to Determine 

7. PhoneUseLocation: Location of hand-held phone during majority of event (not for 

reaching or ending subtasks): applies only to “HH: Dial,” “HH: View/Browse,” “HH: 

Talk/Listen,” “HH: Text,” and “HH: Hold” subtasks. See clock diagram of the steering 

wheel. 

a. No hand-held phone used 

b. N/A, Reaching or ending HH call – choose this option if the subtask being coded 

is “HH: Locate/Reach/Answer” or “HH: End Task.” 

c. In right hand against right ear 

d. In left hand against left ear 

e. In one hand on steering wheel (low) – 5:00-7:00 on a clock. In both hands resting 

on steering wheel (low) 

f. In one hand resting on steering wheel (middle) – 2:00-4:00 or 8:00-10:00 on a 

clock. In both hands resting on steering wheel (middle) 

g. In one hand resting on steering wheel (high) – 11:00-1:00 on a clock. 

h. In both hands resting on steering wheel (high) 

i. In one hand raised out in front of forward view 

j. In both hands raised out in front of forward window 

k. In one hand to side of/in front of steering wheel 

l. In both hands to side of/in front of steering wheel 

m. In one hand below steering wheel 

n. In both hands below steering wheel 

o. In one hand placed in front of mouth 

p. In both hands placed in front of mouth 

q. In right hand against left ear (cross body) 

r. In left hand against right ear (cross body) 

s. Not in hand – Other 

Final Report 

113 

Hand placement on steering wheel diagram 

Low

Middle Middle 

High 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

Page 2 of Question Annotation 

8. AmbientLighting: Ambient Lighting at the Precipitating Event: 

a. Daylight 

b. Dusk – use if the ambient lighting is mostly dark and continues to darken 

throughout the file. Do not use if it the ambient lighting is daylight, but it is 

cloudy. 

c. Darkness, lighted – It is nighttime during the subtask, but the roadway is lighted 

d. Darkness, not lighted – It is nighttime during the subtask, and the roadway is 

NOT lighted 

e. Dawn – use if the ambient lighting is mostly dark and lightens throughout the file. 

Do not use if it the ambient lighting is daylight, but it is cloudy. 

f. Vehicle is Not Outside 

g. Unable to determine 

9. Weather: Weather conditions at the Precipitating Event: 

a. No Adverse Conditions – includes cloudy/overcast skies with no visible falling 

precipitation 

b. Light Rain/Mist 

c. Heavy Rain 

d. Snowing/Sleeting 

e. Fog 

f. Rain + Fog 

g. Snow + Fog 

h. Smoke, Dust - There is smoke and/or dust, either stagnant or blowing, in the air 

i. Other - There is some type of adverse atmospheric condition present, not 

described in other categories 

j. Unable to Determine 

10. RoadSurface: Road surface condition at the Precipitating Event: 

a. Dry - There is no foreign material (rain, snow, oil, etc.) on the roadway in the area 

of the event (nothing on the road to affect the driving task) 

b. Wet - Roadway is completely or partially wet in the area of the event (not snowy, 

icy, muddy, or oily) 

c. Snowy - There is some amount of unmelted snow or slush on the roadway in the 

area of the event, enough to affect the driving task (no ice on the road in the area 

of interest) 

d. Icy - There is some amount of ice on the roadway in the area of the event, enough 

to affect the driving task 

e. Muddy - There is some amount of mud on the roadway in the area of the event, 

enough to affect the driving task 

f. Oily - There is some amount of oil, grease, or other slippery fluid on the roadway 

in the area of the event, enough to affect the driving task 

g. Other - There is some type of foreign substance on the road, not listed in previous 

categories, enough to affect the driving task 

h. Unable to Determine 

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Page 3 of Question Annotation 

11. TrafficFlow: Traffic Flow at the Precipitating Event: Roadway design (including the 

presence or lack of a median) at the start of the event. If the event starts while the driver 

is at an intersection, the traffic flow conditions just prior to the intersection should be 

recorded.

a. Not divided, standard 2-way traffic way - with or without center line, but without 

center 2-way turn lane 

b. Not divided, with center 2-way turn lane 

c. Divided - median strip or barrier separates opposite direction 

d. One-way traffic 

e. No lanes – such as a Parking lot, Driveway, etc. 

f. Other 

g. Unable to determine 

12. ContigTravelLanes: TOTAL number of CONTIGUOUS travel lanes present at 

Precipitating Event, including turn, exit-entrance, and oncoming: includes the total 

number of all: lanes in the direction the driver is driving, oncoming lanes, turn lanes, 

entrance/exit ramps, and lanes with parked vehicles. If the event starts while the driver is 

at an intersection, the number of lanes just prior to the intersection should be recorded

a. 0 (No Lanes) - vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

b. 1 

c. 2 

d. 3 

e. 4 

f. 5 

g. 6 

h. 7 

i. 8+ 

j. Unable to determine 

13. NumDirectLanes: Number of travel through lanes in the DIRECTION OF TRAVEL 

ONLY at the Precipitating Event: includes only the total number of lanes in the 

direction the driver is driving. Do NOT include: oncoming lanes, turn lanes, 

entrance/exit ramps, or lanes with parked vehicles. If the event starts while the driver is at 

an intersection, the number of lanes just prior to the intersection should be recorded 

a. 0 (No Lanes) – vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

b. 1 

c. 2 

d. 3 

e. 4 

f. 5 

g. 6 

h. 7 

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i. 8+ 

j. Unable to determine 

14. StartingLane: In which of the lanes counted in the question above is the driver 

traveling at the Precipitating Event? - Note: Lanes should be counted from left to 

right

a. Not in through lane 

b. 0 (No Lanes) - vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

c. 1 (Left-most lane or only lane) 

d. 2 

e. 3 

f. 4 

g. 5 

h. 6 

i. 7 

j. 8+ 

k. Unable to determine 

Page 4 of Question Annotation 

15. RoadAlignment: Roadway alignment at the Precipitating Event: 

a. Straight – Road alignment is straight 

b. Curve Left – Road alignment is curved to the left 

c. Curve Right – Road alignment is curved to the right 

d. Unable to determine 

16. RoadGrade: Roadway grade at the Precipitating Event: 

a. Level 

b. Grade Up – profile of road is graded, and vehicle is going up a hill 

c. Hillcrest – vehicle is at a hillcrest (area of transition between an upgrade and a 

downgrade) 

d. Grade Down – profile of road is graded, and vehicle is going down a hill 

e. Dip – vehicle is in a dip 

f. Unable to determine 

17. Locality: Locality at the Precipitating Event: 

a. Interstate/bypass/divided highway with no traffic signals 

b. Bypass/divided highway with traffic signals 

c. Business/industrial - Vehicle passes any type of business or industrial structure 

d. Open country - Other than the roadway, there is nothing visible that is described 

in any of the other categories 

e. Residential - Vehicle passes at least one house or evidence of a residential 

neighborhood but does not drive through a business or industrial area. 

f. Construction zone - Vehicle is in a construction zone (construction equipment, 

barrels, etc. are visible) (This category takes precedence over others)

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g. School - Vehicle passes any type of school building, including adult learning 

institutions (This category takes precedence over others)

h. Church (This category takes precedence over others)

i. Playground - Vehicle passes any type of playground or children's playing field 

(This category takes precedence over others)

j. Other - Locality is one not described in other categories 

k. Unable to determine 

18. TrafficDensity: Traffic density at the Precipitating Event: 

a. N/A – Stopped at Intersection 

b. LOS A1: Free flow – No leading traffic in any lane – Subject driver is unaffected 

in the traffic stream because there are no leading vehicles in any lane. Freedom to 

select desired speeds and to maneuver within the traffic stream is at the highest 

level possible. 

c. LOS A2: Free flow – Leading traffic present in at least one lane - Individual 

drivers are virtually unaffected by the presence of others in the traffic stream. 

Freedom to select desired speeds and to maneuver within the traffic stream is 

extremely high. The general level of comfort and convenience provided to the 

motorist, passenger, or pedestrian is excellent. 

d. LOS B: Flow with some restrictions - In the range of stable flow, but the 

presence of other users in the traffic stream begins to be noticeable. Freedom to 

select desired speeds is relatively unaffected, but there is a slight decline in the 

freedom to maneuver within the traffic stream from LOS A. The level of comfort 

and convenience provided is somewhat less than at LOS A, because the presence 

of others in the traffic stream begins to affect individual behavior. 

e. LOS C: Stable flow, maneuverability and speed are more restricted - In the range 

of stable flow, but marks the beginning of the range of flow in which the 

operation of individual users becomes significantly affected by interactions with 

others in the traffic stream. The selection of speed is now affected by the 

presence of others, and maneuvering within the traffic stream requires substantial 

vigilance on the part of the user. The general level of comfort and convenience 

declines noticeably at this level. 

f. LOS D: Unstable flow - temporary restrictions substantially slow driver - Highdensity, but stable flow. Speed and freedom to maneuver are severely restricted, 

and the driver or pedestrian experiences a generally poor level of comfort and 

convenience. Small increases in traffic flow will generally cause operational 

problems at this level. 

g. LOS E: Flow is unstable, vehicles are unable to pass, temporary stoppages, etc. - 

Operating conditions at or near the capacity level. All speeds are reduced to a 

low, but relatively uniform value. Freedom to maneuver within the traffic stream 

is extremely difficult, and it is generally accomplished by forcing a vehicle or 

pedestrian to "give way" to accommodate such maneuvers. Comfort and 

convenience levels are extremely poor, and driver or pedestrian frustration is 

generally high. Operations at this level are usually unstable, because small 

increases in flow or minor perturbations within the traffic stream will cause 

breakdowns. 

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h. LOS F: Forced traffic flow, low speeds, traffic volumes below capacity - Forced 

or breakdown flow. This condition exists wherever the amount of traffic 

approaching a point exceeds the amount which can traverse the point. Queues 

form behind such locations. Operations within the queue are characterized by 

stop-and-go waves, and they are extremely unstable. Vehicles may progress at 

reasonable speeds for several hundred feet or more then be required to stop in a 

cyclic fashion. LOS F is used to describe the operating conditions within the 

queue, as well as the point of the breakdown. It should be noted, however, that in 

many cases operating conditions of vehicles or pedestrians discharged from the 

queue may be quite good. Nevertheless, it is the point at which arrival flow 

exceeds discharge flow, which causes the queue to form, and LOS F is an 

appropriate designation for such points. 

i. Unable to determine 

Page 5 of Question Annotation 

19. LVPresent: Is there a lead vehicle traveling in the same lane at the Precipitating 

Event? 

a. Yes 

b. No (Skip to Page 6) 

c. Unable to determine 

20. LVObjectID (text): What is the object ID of the lead vehicle reported by the radar at 

the Precipitating Event? 

o If there is a lead vehicle reported by the radar, enter the Object ID 

o If radar data is not available, enter “N/A” 

o If unsure, enter “Unable to determine” 

21. LVActualRange (text): What is the X-Range to the lead vehicle reported by the 

radar at the Precipitating Event? 

o If there is a lead vehicle reported by the radar, enter the X_Range 

o If radar data is not available, enter “N/A” 

o If unsure, enter “Unable to determine” 

22. LVEstRange: Estimate the range to the lead vehicle at the Precipitating Event: 

a. Far (Greater than 40 m or 3 standard lane markings away) 

b. Medium (Between 12 and 40 m or 1-3 standard lane markings away) 

c. Close (Less than 12 m or 1 standard lane marking away) 

d. Unable to determine 

e. N/A (No lead vehicle) 

Lead Vehicle Range Estimate Diagrams 

***Standard lane markings are 10 ft. long, and the distance between each one is 30 ft. Thus, 

from the start of one standard marking to the start of the next is 40 feet or about 12 meters. NonFinal Report 

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standard lane markings (such as during a merge or delineating a turn lane) have different 

measurements and cannot be used in this manner. 

Close (Less than 14 m on radar, or just over one standard lane marking) 

 

 

 

Medium (14 to 40 m on radar or 1-3 standard lane markings) 

Far (Greater than 40 m on radar or more than 3 standard lane markings) 

23. LVActualRate (text): What is the relative X-velocity of the lead vehicle reported by 

the radar at the Precipitating Event? 

o If there is a lead vehicle reported by the radar, enter the X_Velocity 

o If radar data is not available, enter “N/A” 

o If unsure, Enter “Unable to determine” 

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24. LVEstRate: Estimate the closing rate to the lead vehicle at the Precipitating Event: 

a. Distance Rapidly Increasing 

b. Distance Increasing 

c. Distance Constant 

d. Distance Closing 

e. Distance Rapidly Closing 

f. Unable to determine 

g. N/A (No lead vehicle) 

Page 6 of Question Annotation 

25. SVLaneChange: Does the subject driver CHOOSE to change lanes during the 10-

second time interval before the Precipitating Event? This 10-second time interval 

includes 5 seconds before the start of the event to 5 seconds after the start of the event. 

a. No - driver does not change lanes, OR any lane change performed is forced by 

lane closure, merging requirements, or turn lane movements 

b. Yes, planned lane change – driver changes lanes based on a choice to travel in a 

different lane. This does NOT include when the driver makes required merges 

(such as merging onto/off of a highway, moving into a turn lane, or lanes 

ending/beginning – all of which should be answered “No”.) 

c. Yes, evasive/unplanned lane change – driver changes lanes in order to avoid an 

accident, or an animal/object/pedestrian in the forward roadway 

d. Unable to determine 

26. SVTurnSignal: If driver changes lanes as above, does he/she use the turn signal? 

a. Driver does not change lanes 

b. Yes 

c. No 

d. Unable to determine 

27. RVPresent: Is there a trailing rear vehicle traveling in the same lane as the driver at 

the Precipitating Event? 

a. Yes 

b. No (Skip to Page 7) 

c. Unable to determine 

28. RVEstRange: Estimate the range to the rear vehicle at the Precipitating Event: 

a. Far (Greater than 40 m or 3 standard lane markings away) 

b. Medium (Between 12 m and 40 m or 1 to 3 standard lane markings away) 

c. Close (Less than 12 m or 1 standard lane marking away) 

d. Unable to determine 

e. N/A (No rear vehicle) 

Rear Vehicle Range Estimate Diagrams 

***Standard lane markings are 10 ft. long, and the distance between each one is 30 ft. Thus 

from the start of one standard marking to the start of the next is 40 feet or about 12 meters. NonFinal Report 

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standard lane markings (such as during a merge or delineating a turn lane) have different 

measurements and cannot be used in this manner. 

Close (Less than14 m or just over one standard lane marking) 

 

 

Far (Greater than 40 m away or more than 3 standard lane markings) 

 

Medium (14 to 40 m or 1-3 standard lane markings) 

29. RVEstRate: Estimate the closing rate of the rear trailing vehicle at the Precipitating 

Event: 

a. Distance Rapidly Increasing 

b. Distance Increasing 

c. Distance Constant 

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d. Distance Closing 

e. Distance Rapidly Closing 

f. Unable to determine 

g. N/A (No rear vehicle) 

30. RVLaneChange: Does the rear trailing vehicle change lanes to pass the subject 

vehicle within 10 seconds before the Precipitating Event? This 10-second time 

interval includes 5 seconds before the start of the event to 5 seconds after the start of the 

event. 

a. Yes, Rear Vehicle Moves to Pass (PLANNED) – Rear vehicle changes lanes 

based on a choice to travel in a different lane or in order to drive at a faster speed 

than the subject. This does NOT include when the rear vehicle makes required 

merges (such as merging onto/off of a highway, moving into a turn lane, or lanes 

ending/beginning – all of which should be answered “No”). 

b. Yes, Rear Vehicle Moves to Pass (EVASIVE) - rear vehicle changes lanes in 

order to avoid an accident, or an animal/object/pedestrian 

c. No – rear vehicle does not change lanes, OR any lane change performed is forced 

by lane closure, merging requirements, or turn lane movements 

d. Unable to determine 

e. N/A (No rear vehicle) 

Page 7 of Question Annotation 

31. RelationToJunction: Relation to junction at the Precipitating Event: 

l. Non-junction – Subject vehicle is not close to a junction (the area formed by the 

connection of two roadways) 

m. Intersection – Subject vehicle is at or within 1 car length (~20 feet) of an 

intersection (roads cross at the same grade) 

n. Intersection-related – Subject vehicle is within 3 car lengths (~60 feet) of an 

intersection (where roads cross at the same grade), either approaching or exiting 

the intersection 

o. Interchange area – Subject vehicle is within the boundaries of an interchange with 

exit and/or entrance ramps present (a road junction that typically utilizes grade 

separation and one or more ramps to permit traffic on at least one road to pass 

through the junction without crossing any other traffic stream) 

p. Entrance ramp – Subject vehicle is on or entering/exiting an entrance ramp (a 

transition roadway connecting two roadways or used for entering through-traffic 

lanes) 

q. Exit ramp – Subject vehicle is on or entering/exiting an exit ramp (a transition 

roadway connecting two roadways or used for exiting through-traffic lanes) 

r. Driveway, alley access, etc. – Subject vehicle is on or entering/exiting a driveway, 

alley, or some other roadway providing access to property adjacent to the traffic 

way 

s. Rail grade crossing – Subject vehicle is close to the at-grade connection of a 

railroad bed and roadway 

t. Parking lot – subject vehicle is within the boundaries of a parking lot 

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u. Other – subject vehicle is related to a junction in a manner not described in other 

categories. This includes tunnels, toll booths, and bridges 

v. Unable to determine 

32. TrafficControlDevice: Traffic control device (if any) in effect at the Precipitating 

Event: 

q. No traffic control - There is no traffic control applicable to the subject vehicle at 

the time of the event 

r. Traffic signal - A traffic signal (by colors or flashing) is controlling some aspect 

of the traffic flow applicable to the subject vehicle 

s. Stop sign 

t. Yield sign 

u. Construction signs/warnings 

v. Slow or warning sign, other 

w. School-zone related sign 

x. Officer or watchman/traffic guard 

y. Traffic lanes marked - There are markings on the road that contain information or 

warnings applicable to the driving task for the subject vehicle (use if NO other 

types of devices/signs are used to convey the same information). Does not 

include Railroad crossings (see below). 

z. No passing signs 

aa. One-way road or street 

bb. Railroad crossing with markings or signs - A railroad crossing with associated 

signage (including markings on the road, signs, cross bucks) is controlling some 

aspect of traffic flow applicable to the subject vehicle 

cc. Railroad crossing with signals - A railroad crossing with associated signals 

(including flashing lights, traffic lights) is controlling some aspect of traffic flow 

applicable to the subject vehicle 

dd. Railroad crossing with gate and signals - A railroad crossing with associated 

gate(s) with or without signals (including flashing lights, traffic lights) Is 

controlling some aspect of traffic flow applicable to the subject vehicle 

ee. Other - There is some type of traffic control device, not described in previous 

categories, controlling some aspect of traffic flow applicable to the subject vehicle 

ff. Unable to determine 

Page 8 of Question Annotation 

33. IntersectionPresent: What is the first type of intersection entered within 10 seconds 

centered on the Precipitating Event? This 10-second time interval includes the start of 

the event to 10 seconds after the start of the subtask (5 seconds after the precipitating 

event).

g. No Intersection Entered – Skip to Page 9 – if this option is selected, SKIP to 

question 36 on page 9 of the question annotation 

h. Signalized – subject’s path through intersection is controlled by a stoplight only 

i. Stop sign – subject’s path through intersection is controlled by a stop sign only 

j. Yield sign – subject’s path through intersection is controlled by a yield sign only 

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k. Uncontrolled – subject’s path through intersection is not controlled by any means 

(no signs nor stoplights) 

l. Unable to determine 

34. IntersectionScan1: For the intersection coded above, does the driver appropriately 

scan for traffic PRIOR to entering the intersection? Proper scanning consists of 

gazing to roadway junctions and NOT driveways, alleyways, or parking lot entrances. 

For a 4-way intersection, a glance to the left and right is required; for a right 3-way 

intersection, a glance to the right is required; for a left 3-way intersection, a glance to the 

left is required, etc. These glances are required regardless of traffic control status (traffic 

light color, etc.). 

e. Yes, driver scans appropriately 

f. No, driver does not scan 

g. Unable to determine 

h. N/A - No intersection entered 

35. IntersectionViolate: What stopping behavior is exhibited at the intersection coded 

above? (use the unit converter to convert to miles per hour)

h. Stop not required 

i. Proper stop performed 

j. Rolling stop (minimum speed <15 mph, but greater than 0) 

k. Complete stop, but past the stop bar/sign AND in path of cross traffic 

l. No stop when stop required (minimum speed is >=15mph) 

m. Unable to determine 

n. N/A - No intersection entered 

36. IntersectionScan2: If the driver stops as first in queue at a light at the intersection 

coded above BEFORE the Precipitating Event, does he/she scan within 6 seconds of 

when the vehicle starts moving? Proper scanning consists of gazing to roadway 

junctions and NOT driveways, alleyways, or parking lot entrances. For a 4-way 

intersection, a glance to the left and right is required; for a right 3-way intersection, a 

glance to the right is required; for a left 3-way intersection, a glance to the left is 

required, etc. These glances are required regardless of traffic control status (traffic light 

color, etc.).

g. N/A, Driver stops after precipitating event (skip to Page 9) 

h. N/A, driver does not stop (skip to Page 9) 

i. N/A, driver stops, but not first in queue at light (skip to Page 9) 

j. Yes, driver scans before moving 

k. No, driver does not scan before moving 

l. Unable to determine 

m. N/A - No intersection entered (skip to Page 9) 

34. IntersectionPhone: If SV was stopped at intersection as in above question, did subject 

complete all complex cell phone subtasks before the vehicle started moving. 

a. N/A, Cell phone use does not occur while vehicle is stopped. 

b. N/A, Cell phone use while stopped is limited to Holding/wearing or Talking only 

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c. No, Complex cell phone subtasks (other than holding/wearing/talking) continue 

after vehicle starts moving 

d. Yes, all complex cell phone subtask(s) completed before vehicle starts moving. 

e. Unsure 

Page 9 of Question Annotation 

35. NumLaneBust (text): Number of unintentional lane busts occurring during this event 

– enter the total number of unintentional lane busts that occur during the entire event. Do 

NOT count intentional lane busts (such as when the driver must swerve to avoid an 

accident or an animal/object/pedestrian in the road, etc.). If there are no unintentional 

lane busts, enter “0” and skip to Page 10. 

36. BeginLaneBust1 (text): Begin timestamp of FIRST lane bust – enter the timestamp of 

the beginning of the first lane that occurs during this event. The timestamp can be found 

in the Collection Navigator at the lower, right-hand side of Hawkeye. 

37. BeginLaneBust2 (text): Begin timestamp of SECOND lane bust – enter the timestamp 

of the beginning of the second lane that occurs during this event. 

 

38. BeginLaneBust3 (text): Begin timestamp of THIRD lane bust – enter the timestamp of 

the beginning of the first third bust that occurs during this event. 

Page 10 of Question Annotation 

39. SecondaryTask1: Secondary Task 1 – Indicate any secondary tasks (up to 3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

40. SecondaryTask2: Secondary Task 2 – Indicate any secondary tasks (up to 3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

41. SecondaryTask3: Secondary Task 3 – Indicate any secondary tasks (up to 3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

42. SecondaryTaskDesc (textbox): Define/Describe OTHER tasks above – For any 

secondary tasks listed as “other,” “unknown,” “other device,” “reaching for object: 

other,” or “holding object: other” above, provide a description. Also use this space to 

further explain anything unusual about the list distractions.

43. BothHandsOff: If cell phone use is listed above, does the driver take both hands off 

the steering wheel during the cell phone task(s) that occur within the 6-second 

window? 

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Questions for SCEs 

a. N/A - No cell use listed above 

b. No, at least one hand is on the wheel for all cell use 

c. Yes, both hands off wheel at least once during cell use 

Secondary Task Description 

No Secondary Task There are no observable signs of driver distraction 

Lost in thought 

Driver performs multiple non-specific eye glances within 6-second 

period of time (not focusing on objects of glances), or appears to be in a 

daze resulting in potential conflict. 

Looked but did not see 

Driver is looking right at (or looks at) where incident occurs, but shows 

no reaction. Often seen when blind spot is checked, but vehicles present 

are not seen. 

Cell Hand-Held: 

Locate/Reach/Answer When the driver looks for or reaches towards his/her hand-held cell 

phone or manipulates it to answer a call. 

Cell Hand-Held: 

Talk/Listen/Voice 

Commands 

When a driver is talking on a hand-held phone or has the phone up to 

his/her ear as if listening to a phone conversation or waiting for a person 

they are calling to pick up the phone. 

NOTE: If the driver uses the speaker phone function on a hand-held cell 

phone: Code as “HH: Talk/Listen/Voice Commands” if the driver keeps 

the hand-held phone in his/her hand(s) while using the speaker phone 

function. Code as “PHF: Talk/Listen/Voice Commands” if the driver 

puts the phone down (thus, does NOT hold it in his/her hand(s)) while 

using the speaker phone function. 

Cell Hand-Held: Dialing When the driver is pressing buttons or interacting with a touch screen on 

a hand-held cell phone in order to dial a phone number to make a call. 

This can include dialing, searching for a contact’s number, entering a 

voice mail password, etc. 

NOTE: This does NOT include pressing a button to answer a call 

(coded as “HH: Locating/Reaching/Answering”) or pressing a button to 

end a call (coded as “HH: End Task”). 

NOTE: Additionally, “HH: Dialing” does NOT include 

pressing buttons or interacting with a touch screen in 

order to type/read a text message (which should be 

coded as “HH: Text messaging” if driver types or 

“HH: Viewing/Browsing/Reading” if driver reads) or 

browse the Internet/use phone applications (which 

should be coded as “HH: 

Viewing/Browsing/Reading”).

Cell Hand-Held: Text 

messaging 

When a driver is pushing buttons or interacting with a touch screen on a 

hand-held cell phone in order to type a text message. 

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NOTE: This does not include reading a text message, which should be 

coded as “HH: Viewing/Browsing/Reading.” 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

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Secondary Task Description 

Cell Hand-Held: 

Viewing/Browsing/Reading 

When the driver views the hand-held cell phone display with or without 

pressing buttons or manipulating the touch screen for a purpose other 

than making/receiving a call or sending a text message. Examples 

include: when the driver uses the cell phone to check time, read a 

received text message, browse the Internet or email, or use the phone’s 

other applications. 

NOTE: If any viewing and/or button manipulation is seen and there is 

NO record of a call being made/received/ended or a text being sent, then 

use this category. Reading a received text message would be coded 

using this category. 

NOTE: Exceptions to this rule: #1 - When a call is ending, code as “HH: 

End Task” if the driver looks at the phone and/or presses a button to end 

a call. #2 - When a call is being answered, any glances or associated 

button presses should be coded as “HH: Locate/Reach/Answer.” 

Cell Hand-Held: Holding When the driver holds a hand-held cell phone in his/her hand but does 

not interact with it. It does NOT count as holding if the phone is resting 

on the driver’s seat (next to or between legs), or on the driver’s lap (both 

of which would end the cell phone interaction and be coded as no cell 

phone task). 

NOTE (The 5-Second Rule): If the subject is viewing, dialing, or 

performing another task with a hand-held phone, then holds the phone 

without visually or manually interacting with it for at least 5,000 

consecutive timestamps (or 5 consecutive seconds), this “break” period 

should be coded as “HH: Holding.” If the driver resumes another (or the 

same) subtask before the 5-consecutive-second period ends, do NOT 

code “HH: Holding.” Rather, continue to code as the initial task until a 

new task begins. 

NOTE: Holding is assumed in all other hand-held subtasks (“HH:...”) 

and does not need to be coded simultaneously with any other hand-held 

task. However, if the phone is being held during any Portable Hands 

Free (PHF) or Integrated Hands Free (IHF) tasks, then “HH: Holding” 

would need to be simultaneously coded. 

Cell Hand-Held: End Task When the driver completes a specific cell phone objective by either 

pressing a button to end the call, putting the phone down after ending a 

call or text, or flipping/sliding the phone closed after ending a call or 

text. 

Cell Integrated Hands-Free: 

Press Button to 

Begin/Answer 

When the driver presses a button on the steering wheel or center stack in 

order to begin a cell phone interaction. This can include pushing to 

answer a call, pushing to voice dial, or pushing to enter a voice 

command. 

Cell Integrated Hands-Free: 

Talk/Listen/Voice 

Commands 

When a driver talks, listens, or gives voice commands on an integrated 

device. Driver must be observed talking repeatedly with no obvious 

passenger interaction. Additionally, this option should only be used 

when the cell records indicate that the driver has made or received a call 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

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Secondary Task Description 

on an integrated hands-free device. 

Cell Integrated Hands-Free: 

Press button to end 

When the driver presses the button on the steering wheel or center stack 

in order to end the cell phone interaction. 

Cell Portable Hands-Free: 

Locate/Put-on 

Headset/Earpiece 

When the driver looks for or reaches towards a headset or earpiece. If 

more than one task occurs (i.e., driver looks for earpiece, reaches for it 

and then puts it in his ear), the first frame number would be the start of 

the first task (reaching for earpiece) and the last frame number coded 

would be the end of the last task (i.e., placing earpiece in ear). 

Cell Portable Hands-Free: 

Holding/Wearing 

Headset/Earpiece 

When a driver is holding a headset/earpiece in his/her hand or wearing it 

on his/her head but not interacting with it (and not involved in a phone 

conversation). Also code as “PHF: Hold/Wearing” if the driver has been 

holding the earpiece/headset in his/her hand(s) for some time and finally 

moves to put it on. It does NOT count as holding if the headset/earpiece 

is resting on the driver’s seat (next to or between legs), or on the driver’s 

lap.

NOTE: If the subject is talking/listening on a portable hands-free device 

or performing another task with a hand-held phone or portable handsfree device, then holds the headset/earpiece in hand or on his/her head 

without interacting for at least 5 consecutive seconds, this “break” period 

should be coded as “PHF: Hold/Wear Headset/Earpiece.” If the driver 

resumes another task before the 5-consecutive-second period ends, do 

NOT code “PHF: Hold/Wear Headset/Earpiece.” 

NOTE: While coding PHF: Talk/Listen, do NOT intersperse PHF: 

Hold/Wear unless is it clear that a phone call has ended. The driver may 

stop talking for periods of time (including breaks longer than 5 seconds) 

to listen to the conversation. This should be coded straight through as 

PHF: Talk/Listen. 

NOTE: Holding/wearing headset or earpiece is assumed in all other 

Portable Hands Free (“PHF:...”) subtasks and does not need to be coded 

simultaneously with any other PHF task. However, if a headset/earpiece 

is being held or worn during any Hand-Held (HH) or Integrated Hands 

Free (IHF) tasks, then “PHF: Holding/Wearing” would need to be 

simultaneously coded. 

Cell Portable Hands-Free: 

Push Button to 

Begin/Answer 

When the driver presses a button on the headset/earpiece in order to 

begin a cell phone interaction. This can include pushing to answer a call 

or pushing to give a voice command to make a call. This button may be 

located on the headset/earpiece itself, or occasionally somewhere on the 

wire connecting the device to the phone.

NOTE: If instead of pushing a button on the headset/earpiece to answer 

or make a call, the driver pushes a button or dials on a hand-held phone, 

this would be coded as “HH: Dialing” or “HH: Locate/Reach/Answer,” 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

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129 

Secondary Task Description 

even if the subsequent conversation takes place via a portable hands-free 

device. 

Cell Portable Hands-Free: 

Talk/Listen/Voice 

Commands 

When a driver is talking on a headset, earpiece, or other aftermarket 

device, OR listening to a phone conversation, OR waiting for a person 

they are calling to pick up the phone. Driver must be observed talking 

repeatedly with no obvious passenger interaction to conclude that the 

headset/earpiece is in use. 

NOTE: This subtask should be coded if the talking subtask is performed 

on a portable hands-free device, even if the dialing, answering, or callending subtasks are performed using a hand-held phone.

NOTE: If the driver uses the speaker phone function 

on a hand-held cell phone: Code as “Hand-Held: 

Talk/Listen/Voice Commands” if the driver keeps 

the hand-held phone in his/her hand(s) while using 

the speaker phone function. Code as “Portable 

Hands-free: Talk/Listen/Voice Commands” if the 

driver puts the phone down (thus, does NOT hold it 

in his/her hand(s)) while using the speaker phone 

function. 

Cell Portable Hands-Free: 

Push Button to End 

When the driver presses the button on the headset/ear piece in order to 

end the cell phone interaction. This button may be located on the 

headset/earpiece itself, or occasionally somewhere on the wire 

connecting the device to the phone.

NOTE: If instead of pushing a button on the headset/earpiece to end a 

call, the driver pushes a button on a hand-held phone, this would be 

coded as “HH: End Task,” even if the conversation took place via a 

Portable Hands-free device. 

Cell Phone Navigation When the driver is using the navigation feature of a hand-held cell 

phone. Is is not entirely clear what this will look like, but it may occur 

when the phone is in a cradle on the dash, or when the driver is clearly 

using the phone for turn-by-turn navigation purposes.

Cell Other Cell Phone Task When a driver is interacting with a hand-held cell phone, portable handsfree device, or integrated hands-free device in some manner not 

described in previous categories. This includes, but is not limited to, the 

following: 

 When the driver plugs a hand-held phone into a power charger. 

 When the subject is playing with a hand-held phone or portable 

hands-free device, or fiddling with them without any purposeful 

manipulation. 

 When the subject puts a hand-held cell phone into a case after 

holding it in his/her hand for 5 or more consecutive seconds after 

other HH tasks have ended. Includes reaching for the separate case, 

maneuvering phone into the case, and then putting it down or 

holding it (coded as holding if longer than 5 seconds). 
 Appendix A.7 Driver, Vehicle, and Environmental 

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130 

Secondary Task Description 

NOTE: If subject must remove a hand-held cell 

phone from the case before using it, code as “HH: 

Locating/Reaching/Answering.” If the subject is 

putting the phone back INTO case immediately 

following a call or text, code it as “HH: End Task.” 

If the subject is putting the phone back INTO a 

case after “HH: Holding,” code as “Other Cell 

Phone Task.” 

Talking/singing/dancing 

(w/o passenger or cell) 

Driver is moving lips as if in conversation or singing a song. Also use if 

driver is moving his/her arms, head, or other body part in time with the 

beat of music 

Mark this if driver is talking or singing or dancing and there is no 

obvious passenger component (either passenger is clearly not present or 

the driver is not looking in the direction of a passenger seat and does not 

turn head as if communicating with someone). 

Reading/Writing 

Driver is reading or writing on material that is in the vehicle, but not a 

part of the vehicle (i.e., not reading external signs, or radio display). 

This could be reading or writing on directions, paper material, 

packaging. If reading a phone number, record as dialing cell phone. 

Cognitive, other 

Driver is emotionally upset or angry, or engaged in another activity not 

included in other categories, that requires the driver to obviously be 

thinking about something other than driving 

Details about condition or emotional state should be specified in the 

appropriate questions. 

Interacting with passenger 

A passenger is visible or not visible, but the driver is clearly interacting 

with a passenger in either the adjacent or rear seat. This could be talking, 

listening, reacting to (e.g., laughing), moving toward or away from the 

passenger (i.e., reaching for the passenger, or avoiding a pat from the 

person). 

Moving object in vehicle 

An object inside the vehicle is in motion and causes the driver to look 

away from the driving task, either due to the motion of the vehicle or due 

to another passenger throwing the object. (Ex. object fell off seat when 

driver stopped hard at a traffic light) 

Insect in vehicle Interaction with any insect in the vehicle (e.g., swatting at insect, moving 

body to avoid insect, looking around trying to locate insect) 

Pet in vehicle 

Any interaction with pet, including petting, talking to, or moving pet or 

interacting with pet carrier. 

Only code if animal/pet is visible at some point in the trip file or if there 

is history/context with the driver and the driver is exhibiting behaviors 

that are appropriate to having a pet in the vehicle 

Object dropped by driver 

Driver is holding something and it drops and the driver then picks it back 

up 

This category supersedes other "reaching" categories in the situation of 

an object being dropped and immediately retrieved 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

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131 

Secondary Task Description 

Reaching for object, other 

Driver reaches for an object not described in any other category. Once 

the driver has finished reaching for the object and has it in hand (if not 

being moved for intended usage), then it becomes "object in vehicle, 

other," as long as it doesn't fit into any of the other categories (e.g., 

eating, drinking, etc.) 

Holding object, other 

Driver is holding an object not described in other categories. Could be 

food, drink, pen, paper, etc. Must continue for at least 5 seconds without 

other manipulations. If less than 5 seconds, code as previous task (e.g., 

reaching for object, personal hygiene). 

Object in vehicle, other 

Driver clearly is looking at, handling, or manipulating an object (visible 

or not) or thing located in the vehicle, other than those listed in other 

categories 

Operating other electronic 

device 

Driver is manipulating some non-manufacturer-installed electronic 

device (PDA, laptop, mp3 player, etc.) either by pressing buttons, 

viewing, opening/closing, plugging in, etc. Reaching for this object 

should be coded as "Reaching for object, other" 

Adjusting radio or HVAC 

Driver interacts with climate control or radio either by touching the 

buttons on the center stack, dashboard, or steering wheel, or glancing at 

the controls. Includes inserting/retrieving CDs and adjusting vents. 

Adjusting/monitoring other 

devices integral to vehicle 

Driver interacts with a manufacturer-installed device other than those 

listed in other categories, either by touching or glancing at the device. 

Includes interaction with seat belt, door locks, sun visor, etc. Does NOT 

include interacting with driving-critical tasks such as turn signal, 

headlights, gear shift, and windshield wipers. 

Looking at non-driving 

related external 

object/event 

Driver is looking outside of the vehicle in the direction of what is 

obviously an object or incident that is not related to the driving task. 

May include looking at an accident, aspects of construction sites/zones, 

animals/pedestrians that are not in or entering the path of travel. 

Only mark if it is clear that the driver is tracking a specific external 

distraction as he/she drives by. Other non-specific or driving-related 

glances should be coded as "Driving-related inattention to forward 

roadway" 

Eating/drinking 

Driver has food or drink that will be put in his/her mouth with or without 

the use of a utensil. If driver is chewing (except gum) also code as 

Eating/drinking. If driver is simply holding food or drink for 5 or more 

seconds, code as Holding Object: Other 

Smoking/tobacco 

Lighting, smoking, or extinguishing cigar or cigarette. Also includes use 

of chewing tobacco or holding a lit cigarette. Reaching for tobacco 

products should be coded "Reaching for object: other" 

Personal hygiene 

Includes applying make-up (including lotion/chapstick), checking self in 

mirror, purposefully fixing/brushing hair, shaving, tweezing, 

brushing/flossing teeth, putting on/removing/adjusting jewelry (including 

watches), putting on/removing/adjusting contacts or glasses. Reaching 

for hygiene-related items should be coded as "Reaching for object: other"

Does not include swiping hair from eyes or quick/thoughtless 

rubbing/scratching, twirling hair. 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

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132 

Secondary Task Description 

Driving-related inattention 

to forward roadway 

Driver glances away from the direction of travel out a window or at a 

side or center mirror for a driving-related issue (i.e., changing lanes, 

crossing through an intersection). Exception: if the vehicle is backing 

and the driver is looking out of the left window to see the road in the 

direction of travel, this is not coded as a distraction. 

Other Secondary Task 

(define in text box) 

Driver is looking in a location other than the direction of travel, in a 

manner not listed in other categories. 

Unknown 

Can't tell or make a judgment whether there is a distraction 

Ex. Part of the video is missing or there is insufficient information in the 

video to make a determination 

Page 11 of Question Annotation 

44. DriverExpectation: If an external incident occurs within the 6-second window, 

describe the driver’s reaction to it: An external incident is anything unexpected or out 

of the ordinary that presents a safety hazard.

g. No external event occurs 

h. Fully expects, drives appropriately/reacts in a timely manner 

i. Somewhat caught off guard, but quickly reacts in appropriate manner 

j. Very much caught off guard, has a delayed reaction (~ > 0.75 s or 750 

timestamps) 

k. Extremely caught off guard, does not react at all 

l. Unable to determine 

45. Emotion: Prior to any external incident noted above, rate the driver’s emotional 

state during the 6-second window: 

h. Neutral/No Emotion Shown 

i. Happy 

j. Angry/Frustrated/Impatient 

k. Sad 

l. Surprised 

m. Other (Could be Concerned/Opinionated/Apologetic/Guilt/Contempt) 

n. Unable to determine 

Driver Emotion Reaction Definitions 

Emotion Operational Definition 

Unable to Determine  Cannot tell what emotion the driver is showing 

Neutral/No Emotion 

Shown 

 The driver has a straight face, does not smile or laugh, does not 

gesture 

Happy  The driver smiles or laughs 

 The driver gestures in excitement 

Angry/Frustrated 

 The driver lowers/squeezes eyebrows, wrinkling forehead 

 The driver clenches his/her teeth 

 The driver yells (opens mouth wide with eyebrows lowered) 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

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133 

Emotion Operational Definition 

 The driver gestures in anger/frustration 

 The driver raises his/her upper lip or tightens lips 

Sad 

 The driver has droopy eyebrows (raises inner eyebrows, lowers 

outer eyebrows) 

 The driver frowns by lowering the outer corners of his/her lips 

Surprised 

 The driver’s eyebrows raise 

 The driver’s mouth opens 

 The driver gestures 

Other  Emotional reaction that does not fit into any other category 

46. EmotionIntensity: Prior to any external incident noted above, rate the intensity of the 

driver’s emotional state during the 6-second window: 

f. Neutral/No Emotion Shown 

g. Slight (Emotion Somewhat Shown) 

h. Marked or Pronounced (Emotion Very Much Shown) 

i. Severe (Emotion Extremely Shown) 

j. Unable to determine 

Driver Emotional Intensity Reduction Definitions 

Intensity of Emotion Operational Definition 

Unable to Determine  Cannot tell the intensity of the emotion 

Neutral/No Emotion Shown 

 The driver has a straight face, does not smile or laugh, 

does not gesture 

 Note: will always be selected if Neutral/No Emotion is 

selected above 

Slight (Emotion Somewhat 

Shown) 

 The driver no longer has a straight face 

 However, no gesturing or head movement is observed 

Marked or Pronounced 

(Emotion Very Much 

Shown) 

 The driver no longer has a straight face 

 The driver gestures one time in a reserved manner 

 The driver moves his head one time 

Severe (Emotion Extremely 

Shown) 

 The driver has wide eyes and a wide open mouth 

 The driver is screaming 

 The driver gestures wildly, or the driver moves his head 

frequently 

47. RaterSurprise As the analyst, how surprised/shocked/interested were you by the 

video captured during this event? 

f. No heightened level of surprise/shock/interest 

g. Somewhat surprised/shocked/interested 

h. Very much surprised/shocked/interested 

i. Extremely surprised/shocked/interested 

j. Unable to determine 
 Appendix A.7 Driver, Vehicle, and Environmental 

Questions for SCEs 

48. NoteComments (text): General Notes/Comments – include descriptions of any instances 

where you coded “Unable to determine” or “Other” in the questions above. As well as 

notes about any other circumstances that help to explain your responses and/or better 

define the conditions and occurrences of this event. Other notes you should type in 

include (but are not limited to) when the driver gets out of the vehicle during an event 

and particularly extreme weather conditions.

Final Report 

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 Appendix A.8 Characterizatio

Final Report 

135 

A.8 Characterization of Safety-Critical Events 

Event Nature 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Conflict with a lead vehicle 153 (37%) 3 (75%) 0 (0%) 20 (28%) 130 (Conflict with vehicle in adjacent lane 74 (18%) 0 (0%) 0 (0%) 27 (38%) 47 (No known conflict (non-conflict incidents) 72 (17%) 0 (0%) 0 (0%) 0 (0%) 1 (0Conflict with animal 20 (5%) 1 (25%) 0 (0%) 1 (1%) 18 (Conflict with vehicle turning across another vehicle path (opposite direction) 15 (4%) 0 (0%) 0 (0%) 2 (3%) 13 (Conflict with merging vehicle 13 (3%) 0 (0%) 0 (0%) 4 (6%) 9 (3Conflict with vehicle turning into another vehicle path (same direction) 13 (3%) 0 (0%) 0 (0%) 3 (4%) 10 (Conflict with pedestrian 13 (3%) 0 (0%) 0 (0%) 2 (3%) 11 (Conflict with vehicle moving across another vehicle path (through intersection) 11 (3%) 0 (0%) 0 (0%) 3 (4%) 8 (3Conflict with oncoming traffic 8 (2%) 0 (0%) 0 (0%) 4 (6%) 4 (2Conflict with obstacle/object in roadway 8 (2%) 0 (0%) 2 (100%) 3 (4%) 3 (Conflict with a following vehicle 6 (1%) 0 (0%) 0 (0%) 1 (1%) 5 (2Conflict with pedalcyclist 3 (1%) 0 (0%) 0 (0%) 0 (0%) 3 (Single-vehicle conflict 2 (0%) 0 (0%) 0 (0%) 1 (1%) 1 (0Conflict with vehicle turning across another vehicle path (same direction) 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Conflict with parked vehicle 1 (0%) 0 (0%) 0 (0%) 1 (1%) 0 (0Conflict with vehicle turning into another vehicle path (opposite direction) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unknown conflict 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

Total 413 (100%) 4 (100%) 2 (100%) 72 (100%) 264 (1
 Appendix A.8 Characterizatio

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136 

Number of Vehicles/Non-Motorists Involved 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

0 100 (24%) 1 (25%) 2 (100%) 5 (7%) 21 (1 300 (73%) 3 (75%) 0 (0%) 64 (89%) 233 (2 11 (3%) 0 (0%) 0 (0%) 3 (4%) 8 (33 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (04 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (05 or more 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Unknown 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

Total 413 (100%) 4 (100%) 2 (100%) 72 (100%) 264 (1
 Appendix A.8 Characterizatio

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137 

Vehicle Type 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Automobile 139 (34%) 3 (75%) 0 (0%) 33 (46%) 103 (Not applicable 75 (18%) 0 (0%) 0 (0%) 1 (1%) 3 (Sport utility vehicle 75 (18%) 0 (0%) 0 (0%) 18 (25%) 57 (2Van (minivan or standard van) 27 (7%) 0 (0%) 0 (0%) 5 (7%) 22 (Pickup truck 26 (6%) 0 (0%) 0 (0%) 2 (3%) 24 (Animal 20 (5%) 1 (25%) 0 (0%) 1 (1%) 18 (Pedestrian 13 (3%) 0 (0%) 0 (0%) 2 (3%) 11 (Tractor-trailer: Enclosed box 10 (2%) 0 (0%) 0 (0%) 3 (4%) 7 (3Object 6 (1%) 0 (0%) 2 (100%) 3 (4%) 1 (0Unknown vehicle type 4 (1%) 0 (0%) 0 (0%) 2 (3%) 2 (Single-unit straight truck: Box 3 (1%) 0 (0%) 0 (0%) 2 (3%) 1 (0Single-unit straight truck: Dump 3 (1%) 0 (0%) 0 (0%) 0 (0%) 3 (Pedalcyclist 3 (1%) 0 (0%) 0 (0%) 0 (0%) 3 (Tractor-trailer, other 2 (0%) 0 (0%) 0 (0%) 0 (0%) 2 (Greyhound bus 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Single-unit straight truck: Multistop/step van 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Tractor only 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Tractor-trailer: Flatbed 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Tractor-trailer: Multiple box 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Other large construction equipment 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Other vehicle type 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0School bus 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Transit bus 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Conversion bus 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Single-unit straight truck: Garbage/recycling 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Single-unit straight truck: Concrete mixer 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Single-unit straight truck: Beverage 0(0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Single-unit straight truck: Flatbed 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Single-unit straight truck: Tow truck 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Single-unit straight truck, other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Single-unit straight truck, unknown 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Straight truck + trailer 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Tractor-trailer: Livestock 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Tractor-trailer: Lowboy trailer 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0
 Appendix A.8 Characterizatio

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138 

Vehicle Type 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Tractor-trailer: Dump trailer 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Tractor-trailer: Multiple grain 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Motorcycle or moped 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Ambulance 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Fire truck/car 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Police 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

Total 413 (100%) 4 (100%) 2 (100%) 72 (100%) 264 (1
 Appendix A.8 Characterizatio

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139 

Precipitating Event 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Other vehicle ahead - decelerating 81 (20%) 0 (0%) 0 (0%) 7 (10%) 74 (2Other event not attributed to subject vehicle 58 (14%) 0 (0%) 0 (0%) 0 (0%) 1 (0Other vehicle lane change - left in front of subject 39 (9%) 0 (0%) 0 (0%) 7 (10%) 32 (Other vehicle ahead - slowed and stopped 2 seconds or less 38 (9%) 3 (75%) 0 (0%) 9 (13%) 26 (Other vehicle lane change - right in front of subject 21 (5%) 0 (0%) 0 (0%) 8 (11%) 13 (Other vehicle entering intersection - left turn across path 18 (4%) 0 (0%) 0 (0%) 3 (4%) 15 (Animal in roadway 16 (4%) 1 (25%) 0 (0%) 1 (1%) 14 (Other vehicle encroaching into lane, over left lane line 13 (3%) 0 (0%) 0 (0%) 3 (4%) 10 (Other vehicle encroaching into lane, over right lane line 11 (3%) 0 (0%) 0 (0%) 4 (6%) 7 (3Subject in intersection - turning left 10 (2%) 0 (0%) 0 (0%) 1 (1%) 4 (2Other vehicle ahead - stopped on roadway more than 2 seconds 10 (2%) 0 (0%) 0 (0%) 4 (6%) 6 (2Pedestrian in roadway 8 (2%) 0 (0%) 0 (0%) 2 (3%) 6 (2Other vehicle entering intersection - straight across path 7 (2%) 0 (0%) 0 (0%) 3 (4%) 4 (2Subject in intersection - passing through 6 (1%) 0 (0%) 0 (0%) 0 (0%) 1 (0Subject vehicle ahead - decelerating 6 (1%) 0 (0%) 0 (0%) 1 (1%) 5 (2Other vehicle lane change - left, sideswipe threat 6 (1%) 0 (0%) 0 (0%) 4 (6%) 2 (Other vehicle lane change - right, sideswipe threat 6 (1%) 0 (0%) 0 (0%) 4 (6%) 2 (Subject in intersection - turning right 5 (1%) 0 (0%) 0 (0%) 0 (0%) 1 (0Other vehicle entering intersection - turning same direction 5 (1%) 0 (0%) 0 (0%) 2 (3%) 3 (Other vehicle from driveway - turning into same direction 4 (1%) 0 (0%) 0 (0%) 0 (0%) 4 (2Pedestrian approaching roadway 4 (1%) 0 (0%) 0 (0%) 0 (0%) 4 (2Animal approaching roadway 4 (1%) 0 (0%) 0 (0%) 0 (0%) 4 (2Object approaching roadway 4 (1%) 0 (0%) 1 (50%) 2 (3%) 1 (0Subject over left lane line into oncoming traffic way 3 (1%) 0 (0%) 0 (0%) 2 (3%) 1 (0Subject over right edge of road 3 (1%) 0 (0%) 1 (50%) 1 (1%) 1 (0Subject lane change - left behind vehicle 3 (1%) 0 (0%) 0 (0%) 0 (0%) 3 (
 Appendix A.8 Characterizatio

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Precipitating Event 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Other vehicle ahead - at a slower constant speed 3 (1%) 0 (0%) 0 (0%) 0 (0%) 3 (Subject lane change - right in front of vehicle 2 (0%) 0 (0%) 0 (0%) 0 (0%) 2 (Subject lane change - left, sideswipe threat 2 (0%) 0 (0%) 0 (0%) 0 (0%) 2 (Subject lane change - right, sideswipe threat 2 (0%) 0 (0%) 0 (0%) 1 (1%) 1 (0Subject lane change - right, other 2 (0%) 0 (0%) 0 (0%) 0 (0%) 2 (Other vehicle - backing 2 (0%) 0 (0%) 0 (0%) 1 (1%) 1 (0Other vehicle entering intersection - intended path unknown 2 (0%) 0 (0%) 0(0%) 0 (0%) 2 (Pedalcyclist/other non-motorist in roadway 2 (0%) 0 (0%) 0 (0%) 0 (0%) 2 (Object in roadway 2 (0%) 0 (0%) 0 (0%) 0 (0%) 2 (This vehicle lost control - other cause 1 (0%) 0 (0%) 0 (0%) 1 (1%) 0 (0Subject over left edge of road 1 (0%) 0 (0%) 0 (0%) 1 (1%) 0 (0Subject lane change - right behind vehicle 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Subject vehicle ahead - at a slower constant speed 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Other vehicle oncoming - over left line 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0This vehicle lost control - blow-out or flat tire 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0This vehicle lost control - stalled engine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0This vehicle lost control - disabling vehicle failure 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0This vehicle lost control - minor vehicle failure 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0This vehicle lost control - poor road conditions 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0This vehicle lost control - excessive speed 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0This vehicle lost control - unknown cause 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 0Subject over right lane line into oncoming traffic way 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Subject vehicle - end departure 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Subject vehicle ahead - stopped on roadway more than 2 seconds 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Subject vehicle ahead - slowed and stopped 2 seconds or less 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Subject lane change - left in front of vehicle 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Subject lane change - left, other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Subject vehicle making a U-turn 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Subject vehicle ahead - other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle ahead - accelerating 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0
 Appendix A.8 Characterizatio

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Precipitating Event 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Other vehicle - traveling in opposite direction 0 (0%) 0 (0%) 0(0%) 0 (0%) 0 (0Other vehicle - in crossover 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle - making U-turn 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (Other vehicle lane change - left behind subject 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle lane change - right behind subject 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle lane change - left other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle lane change - right other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle oncoming - over right line 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle from parallel/diagonal parking lane 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle entering intersection - turning onto opposite direction 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle from driveway - straight across path 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle from driveway - turning into opposite direction 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle from driveway - intended path unknown 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other vehicle from entrance to limited access highway 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Pedestrian in unknown location 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Pedalcyclist/other non-motorist approaching roadway 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Pedalcyclist/other non-motorist in unknown location 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Animal in unknown location 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Object in unknown location 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unknown 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

142 

Which Vehicle is Considered to be at Fault? 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Subject driver 254 (62%) 3 (75%) 2 (100%) 38 (53%) 140 (Driver 2 124 (30%) 0 (0%) 0 (0%) 30 (42%) 94 (3Unknown 1 (0%) 0 (0%) 0 (0%) 1 (1%) 0 (0Not applicable 32 (8%) 1 (25%) 0 (0%) 3 (4%) 28 (Driver 3 2 (0%) 0 (0%) 0 (0%) 0 (0%) 2 (

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 Appendix A.8 Characterizatio

Final Report 

143 

Subject Driver Reaction 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Braked (no lockup) 329 (80%) 2 (50%) 1 (50%) 39 (54%) 219 (Braked and steered left 39 (9%) 0 (0%) 0 (0%) 18 (25%) 21 (Braked and steered right 32 (8%) 1 (25%) 0 (0%) 12 (17%) 19 (No reaction 7 (2%) 1 (25%) 0 (0%) 1 (1%) 2 (Steered to left 2 (0%) 0 (0%) 0 (0%) 1 (1%) 1 (0Steered to right 2 (0%) 0 (0%) 0 (0%) 1 (1%) 1 (0Accelerated and steered right 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Other actions 1 (0%) 0 (0%) 1 (50%) 0 (0%) 0 (0No driver present 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Braked (lockup) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Braked (lockup unknown) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Released brakes 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Accelerated 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Accelerated and steered left 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unknown if action was attempted 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

144 

Incident Type 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Rear-end, striking 176 (43%) 3 (75%) 0 (0%) 25 (35%) 148 (Sideswipe, same direction (left or right) 65 (16%) 0 (0%) 0 (0%) 26 (36%) 39 (Other 62 (15%) 0 (0%) 1 (50%) 3 (4%) 4 (2Turn across path 23 (6%) 0 (0%) 0 (0%) 4 (6%) 19 (Violation of stop sign or signal at intersection 20 (5%) 0 (0%) 0 (0%) 2 (3%) 1 (0Animal-related 20 (5%) 1 (25%) 0 (0%) 1 (1%) 18 (Pedestrian-related 13 (3%) 0 (0%) 0 (0%) 2 (3%) 11 (Turn into path (same direction) 10 (2%) 0 (0%) 0 (0%) 3 (4%) 7 (3Straight crossing path, not involving sign/signal violation 7 (2%) 0 (0%) 0 (0%) 1 (1%) 6 (2Rear-end, struck 6 (1%) 0 (0%) 0 (0%) 1 (1%) 5 (2Opposite direction (head-on or sideswipe) 4 (1%) 0 (0%) 0 (0%) 2 (3%) 2 (Road departure (left or right) 3 (1%) 0 (0%) 1 (50%) 1 (1%) 1 (0Pedalcyclist-related 3 (1%) 0 (0%) 0 (0%) 0 (0%) 3 (Backing into traffic 1 (0%) 0 (0%) 0 (0%) 1 (1%) 0 (0Road departure (end) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Turn into path (opposite direction) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Backing, fixed object 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unknown 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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Final Report 

145 

Driver Impairments 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

None apparent 298 (72%) 0 (0%) 1 (50%) 41 (57%) 190 (Distracted 99 (24%) 2 (50%) 1 (50%) 27 (38%) 65 (2Drowsy, sleepy, asleep, fatigued 12 (3%) 2 (50%) 0 (0%) 3 (4%) 6 (2Angry 2 (0%) 0 (0%) 0 (0%) 1 (1%) 1 (0Other emotional state 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Other 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0Ill, blackout 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Drugs, medication 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Drugs, alcohol 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other illicit drugs 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Restricted to wheelchair 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Impaired due to previous injury 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Deaf 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unknown 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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Final Report 

146 

Driver Seat Belt Use 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Yes, belt worn 403 (98%) 4 (100%) 2 (100%) 72 (100%) 259 (No, belt NOT worn 10 (2%) 0 (0%) 0 (0%) 0 (0%) 5 (2Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

147 

Ambient Lighting 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Daylight 348 (84%) 3 (75%) 2 (100%) 61 (85%) 228 (Darkness, lighted 28 (7%) 1 (25%) 0 (0%) 6 (8%) 12 (Darkness, not lighted 27 (7%) 0 (0%) 0 (0%) 3 (4%) 17 (Dusk 10 (2%) 0 (0%) 0 (0%) 2 (3%) 7 (3Dawn 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Vehicle is Not Outside 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unable to Determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

148 

Weather Conditions 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

No Adverse Conditions 385 (93%) 4 (100%) 2 (100%) 64 (89%) 250 (Light Rain/Mist 20 (5%) 0 (0%) 0 (0%) 7 (10%) 9 (3Heavy Rain 8 (2%) 0 (0%) 0 (0%) 1 (1%) 5 (2Snowing/Sleeting 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Fog 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Rain + Fog 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Snow + Fog 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Smoke, dust 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

149 

Trafficway Flow 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Divided 280 (68%) 1 (25%) 0 (0%) 50 (69%) 177 (Not divided, standard 2-way traffic way 104 (25%) 3 (75%) 0 (0%) 16 (22%) 68 (2One-way traffic 14 (3%) 0 (0%) 1 (50%) 2 (3%) 10 (Not divided, with center 2-way turn lane 10 (2%) 0 (0%) 0 (0%) 3 (4%) 6 (2No lanes 5 (1%) 0 (0%) 1 (50%) 1 (1%) 3 (Other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

150 

Number of Traffic Lanes 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

CrashRelevan

Conflict

N (%) 

0 (No Lanes) 5 (1%) 0 (0%) 1 (50%) 1 (1%) 3 (1%) 1 11 (3%) 0 (0%) 1 (50%) 2 (3%) 7 (3%) 2 145 (35%) 2 (50%) 0 (0%) 21 (29%) 105 (40%3 110 (27%) 0 (0%) 0 (0%) 20 (28%) 66 (25%4 87 (21%) 1 (25%) 0 (0%) 15 (21%) 54 (20%5 39 (9%) 1 (25%) 0 (0%) 9 (13%) 22 (8%6 16 (4%) 0 (0%) 0 (0%) 4 (6%) 7 (3%) 7 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 8+ 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%) Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 

Total 413 (100%) 4 (100%) 2 (100%) 72 (100%) 264 (100%
 Appendix A.8 Characterizatio

Final Report 

151 

Locality 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Business/industrial 130 (31%) 1 (25%) 2 (100%) 26 (36%) 71 (2Interstate/bypass/divided highway with no traffic signals 117 (28%) 1 (25%) 0 (0%) 22 (31%) 92 (3Bypass/divided highway with traffic signals 49 (12%) 0 (0%) 0 (0%) 4 (6%) 19 (Open country 37 (9%) 1 (25%) 0 (0%) 4 (6%) 23 (Residential 37 (9%) 1 (25%) 0 (0%) 8 (11%) 25 (Construction zone 32 (8%) 0 (0%) 0 (0%) 5 (7%) 26 (1School 9 (2%) 0 (0%) 0 (0%) 2 (3%) 7 (3Church 2 (0%) 0 (0%) 0 (0%) 1 (1%) 1 (0Playground 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

152 

Traffic Density 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

N/A – Stopped at Intersection 5 (1%) 0 (0%) 1 (50%) 1 (1%) 2 (LOS A1: Free flow – No leading traffic in any lane 104 (25%) 0 (0%) 1 (50%) 14 (19%) 45 (LOS A2: Free flow – Leading traffic present in at least one lane 122 (30%) 1 (25%) 0 (0%) 21 (29%) 78 (3LOS B: Flow with some restrictions 125 (30%) 0 (0%) 0 (0%) 25 (35%) 96 (3LOS C: Stable flow, maneuverability and speed are more restricted 35 (8%) 1 (25%) 0 (0%) 6 (8%) 28 (LOS D: Unstable flow - temporary restrictions substantially slow driver 15 (4%) 2 (50%) 0 (0%) 1 (1%) 12 (LOS E: Flow is unstable, vehicles are unable to pass, temporary stoppages, etc. 6 (1%) 0 (0%) 0 (0%) 3 (4%) 3 (LOS F: Forced traffic flow, low speeds, traffic volumes below capacity 1 (0%) 0 (0%) 0 (0%) 1 (1%) 0 (0Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

Total 413 (100%) 4 (100%) 2 (100%) 72 (100%) 264 (1
 Appendix A.8 Characterizatio

Final Report 

153 

Relation to Junction 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

Non-junction 264 (64%) 2 (50%) 0 (0%) 34 (47%) 186 (Intersection 55 (13%) 1 (25%) 1 (50%) 14 (19%) 18 (Interchange area 40 (10%) 1 (25%) 0 (0%) 9 (13%) 28 (Intersection-related 33 (8%) 0 (0%) 0 (0%) 11 (15%) 18 (Entrance ramp 10 (2%) 0 (0%) 0 (0%) 2 (3%) 7 (3Parking lot 6 (1%) 0 (0%) 1 (50%) 1 (1%) 4 (2Exit ramp 3 (1%) 0 (0%) 0 (0%) 0 (0%) 3 (Other 2 (0%) 0 (0%) 0 (0%) 1 (1%) 0 (0Driveway, alley access, etc. 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Rail grade crossing 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

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 Appendix A.8 Characterizatio

Final Report 

154 

Traffic Control Device 

Total SafetyCritical 

Events 

N (%) 

Crashes 

N (%) 

Curb Strikes 

N (%) 

Near-Crashes 

N (%) 

Cra

Rele

Con

N (

No traffic control 263 (64%) 3 (75%) 2 (100%) 50(69%) 201 (Traffic signal 113 (27%) 1 (25%) 0 (0%) 15 (21%) 35 (Slow or warning sign, other 14 (3%) 0 (0%) 0 (0%) 3 (4%) 11 (Stop sign 8 (2%) 0 (0%) 0 (0%) 3 (4%) 3 (Construction signs/warnings 8 (2%) 0 (0%) 0 (0%) 0 (0%) 8 (3Traffic lanes marked 6 (1%) 0 (0%) 0 (0%) 1 (1%) 5 (2Yield sign 1 (0%) 0 (0%) 0 (0%) 0 (0%) 1 (0School-zone related sign 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Officer or watchman/traffic guard 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0No passing signs 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0One-way road or street 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Railroad crossing with markings or signs 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Railroad crossing with signals 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Railroad crossing with gate and signals 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Other 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0Unable to determine 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0

Total 413 (100%) 4 (100%) 2 (100%) 72 (100%) 264 (1
 Appendix A.8 Characterizatio

Figure 8. SCE Rate per Driver by Gender and Age Group 

.

Final Report 

155 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

A.9 Driver, Vehicle, and Environmental Questions for SafetyCritical Event Baseline Periods 

Baseline periods for safety-critical events were identified by randomly selecting 6-second epochs 

of driving for each driver in the Cell Phone Pilot database. These baseline periods were selected 

from all driving events over 5 mph, and are stratified by miles driven. This protocol provides 

instructions on how to complete the reduction for environmental and driver-related factors during 

these baseline events. 

Page 1 of Question Annotation 

37. Seatbelt: Driver seatbelt use at start of 6-second baseline: 

a. Yes, belt worn 

b. No, belt NOT worn 

c. Unable to determine 

38. HHPhoneType: Type of hand-held phone the driver uses for the majority of the 

event: 

a. No hand-held phone used (Skip to Page 2) 

b. Standard keys on front of phone 

c. Vertical flip-phone 

d. Horizontal flip-phone/Slide keyboard 

e. Touch screen 

f. BlackBerry/QWERTY on Front 

g. Unable to determine 

39. PhonePriorLocation: Location of hand-held phone prior to being reached for 

(Reaching subtasks only): applies only to “HH: Locate/Reach/Answer” subtasks 

bb. No hand-held phone used 

cc. Reaching for phone does not occur – choose this option if the subtask being coded 

is an HH task other than “HH: Locate/Reach/Answer” (such as, “HH: 

Talk/Listen,” “HH: Text,” etc.) 

dd. Shirt/Jacket Pocket 

ee. Pants Pocket 

ff. Cup Holder 

gg. On Dash (not in cradle) 

hh. Purse (if seen) 

ii. Passenger seat 

jj. In cradle – usually found attached to dash or windshield 

kk. Glove box 

ll. Center Console storage 

mm. Other 

nn. Unable to determine 

Final Report 

156 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

40. PhoneUseLocation: Location of hand-held phone during majority of event (not for 

reaching or ending subtasks): applies only to “HH: Dial,” “HH: View/Browse,” “HH: 

Talk/Listen,” “HH: Text,” and “HH: Hold” subtasks. No hand-held phone used 

t. N/A, Reaching or ending HH call – choose this option if the subtask being coded 

is “HH: Locate/Reach/Answer” or “HH: End Task.” 

u. In right hand against right ear 

v. In left hand against left ear 

w. In one hand on steering wheel (low) – 5:00-7:00 on a clock. 

x. In both hands resting on steering wheel (low) 

y. In one hand resting on steering wheel (middle) – 2:00-4:00 or 8:00-10:00 on a 

clock. 

z. In both hands resting on steering wheel (middle) 

aa. In one hand resting on steering wheel (high) – 11:00-1:00 on a clock. 

bb. In both hands resting on steering wheel (high) 

cc. In one hand raised out in front of forward view 

dd. In both hands raised out in front of forward window 

ee. In one hand to side of/in front of steering wheel 

ff. In both hands to side of/in front of steering wheel 

gg. In one hand below steering wheel 

hh. In both hands below steering wheel 

ii. In one hand placed in front of mouth 

jj. In both hands placed in front of mouth 

kk. In right hand against left ear (cross body) 

ll. In left hand against right ear (cross body) 

mm. Not in hand – Other 

Page 2 of Question Annotation 

41. AmbientLighting: Ambient Lighting at start of 6-second baseline: 

h. Daylight 

Final Report 

157 

Hand placement on steering wheel diagram 

Middle Middle 

High 

Low 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

i. Dusk – use if the ambient lighting is mostly dark and continues to darken 

throughout the file. Do not use it if the ambient lighting is daylight, but it is 

cloudy. 

j. Darkness, lighted – It is nighttime during the subtask, but the roadway is lighted 

k. Darkness, not lighted – It is nighttime during the subtask, and the roadway is 

NOT lighted 

l. Dawn – use if the ambient lighting is mostly dark and lightens throughout the file. 

Do not use if it the ambient lighting is daylight, but it is cloudy. 

m. Vehicle is Not Outside 

n. Unable to determine 

42. Weather: Weather conditions at start of 6-second baseline: 

a. No Adverse Conditions – includes cloudy/overcast skies with no visible falling 

precipitation 

b. Light Rain/Mist 

c. Heavy Rain 

d. Snowing/Sleeting 

e. Fog 

f. Rain + Fog 

g. Snow + Fog 

h. Smoke, dust - There is smoke and/or dust, either stagnant or blowing, in the air 

i. Other - There is some type of adverse atmospheric condition present, not 

described in other categories 

j. Unable to determine 

43. RoadSurface: Road surface condition at start of 6-second baseline: 

a. Dry - There is no foreign material (rain, snow, oil, etc.) on the roadway in the area 

of the event (nothing on the road to affect the driving task) 

b. Wet - Roadway is completely or partially wet in the area of the event (not snowy, 

icy, muddy, or oily) 

c. Snowy - There is some amount of unmelted snow or slush on the roadway in the 

area of the event, enough to affect the driving task (no ice on the road in the area 

of interest) 

d. Icy - There is some amount of ice on the roadway in the area of the event, enough 

to affect the driving task 

e. Muddy - There is some amount of mud on the roadway in the area of the event, 

enough to affect the driving task 

f. Oily - There is some amount of oil, grease, or other slippery fluid on the roadway 

in the area of the event, enough to affect the driving task 

g. Other - There is some type of foreign substance on the road, not listed in previous 

categories, enough to affect the driving task 

h. Unable to determine 

Page 3 of Question Annotation 

Final Report 

158 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

44. TrafficFlow: Traffic Flow at start of 6-second baseline: Roadway design (including the 

presence or lack of a median) at the start of the event. If the event starts while the driver 

is at an intersection, the traffic flow conditions just prior to the intersection should be 

recorded.

a. Not divided, standard 2-way traffic way - with or without center line, but without 

center 2-way turn lane 

b. Not divided, with center 2-way turn lane 

c. Divided - median strip or barrier separates opposite direction 

d. One-way traffic 

e. No lanes – such as a Parking lot, Driveway, etc. 

f. Other 

g. Unable to determine 

45. ContigTravelLanes: TOTAL number of CONTIGUOUS travel lanes present at start 

of 6-second baseline, including turn, exit-entrance, and oncoming: includes the total 

number of all: lanes in the direction the driver is driving, oncoming lanes, turn lanes, 

entrance/exit ramps, and lanes with parked vehicles. If the event starts while the driver is 

at an intersection, the number of lanes just prior to the intersection should be recorded

a. 0 (No Lanes) - vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

b. 1 

c. 2 

d. 3 

e. 4 

f. 5 

g. 6 

h. 7 

i. 8+ 

j. Unable to determine 

46. NumDirectLanes: Number of travel through lanes in the DIRECTION OF TRAVEL 

ONLY at start of 6 second baseline: includes only the total number of lanes in the 

direction the driver is driving. Do NOT include: oncoming lanes, turn lanes, 

entrance/exit ramps, or lanes with parked vehicles. If the event starts while the driver is at 

an intersection, the number of lanes just prior to the intersection should be recorded 

a. 0 (No Lanes) – vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

b. 1 

c. 2 

d. 3 

e. 4 

f. 5 

g. 6 

h. 7 

i. 8+ 

j. Unable to determine 

Final Report 

159 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

47. StartingLane: In which of the lanes counted in the question above is the driver 

traveling at start of 6-second baseline? - Note: Lanes should be counted from left to 

right

a. Not in through lane 

b. 0 (No Lanes) - vehicle is not in an area intended for traffic. This option should be 

used if the driver is in a parking lot area or on a roadway with no true lanes. 

c. 1 (Left-most lane or only lane) 

d. 2 

e. 3 

f. 4 

g. 5 

h. 6 

i. 7 

j. 8+ 

k. Unable to determine 

Page 4 of Question Annotation 

48. RoadAlignment: Roadway alignment at start of 6-second baseline: 

a. Straight – Road alignment is straight 

b. Curve Left – Road alignment is curved to the left 

c. Curve Right – Road alignment is curved to the right 

d. Unable to determine 

49. RoadGrade: Roadway grade at start of 6-second baseline: 

a. Level 

b. Grade Up – profile of road is graded, and vehicle is going up a hill 

c. Hillcrest – vehicle is at a hillcrest (area of transition between an upgrade and a 

downgrade) 

d. Grade Down – profile of road is graded, and vehicle is going down a hill 

e. Dip – vehicle is in a dip 

f. Unable to determine 

50. Locality: Locality at start of 6-second baseline: 

a. Interstate/bypass/divided highway with no traffic signals 

b. Bypass/divided highway with traffic signals 

c. Business/industrial - Vehicle passes any type of business or industrial structure 

d. Open country - Other than the roadway, there is nothing visible that is described 

in any of the other categories 

e. Residential - Vehicle passes at least one house or evidence of a residential 

neighborhood but does not drive through a business or industrial area. 

f. Construction zone - Vehicle is in a construction zone (construction equipment, 

barrel, etc. are visible) (This category takes precedence over others)

g. School - Vehicle passes any type of school building, including adult learning 

institutions (This category takes precedence over others)

h. Church (This category takes precedence over others)

Final Report 

160 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

i. Playground - Vehicle passes any type of playground or children's playing field 

(This category takes precedence over others)

j. Other - Locality is one not described in other categories 

k. Unable to determine 

51. TrafficDensity: Traffic density at start of 6-second baseline: 

a. N/A – Stopped at Intersection 

b. LOS A1: Free flow – No leading traffic in any lane – Subject driver is unaffected 

in the traffic stream because there are no leading vehicles in any lane. Freedom to 

select desired speeds and to maneuver within the traffic stream is at the highest 

level possible. 

c. LOS A2: Free flow – Leading traffic present in at least one lane - Individual 

drivers are virtually unaffected by the presence of others in the traffic stream. 

Freedom to select desired speeds and to maneuver within the traffic stream is 

extremely high. The general level of comfort and convenience provided to the 

motorist, passenger, or pedestrian is excellent. 

d. LOS B: Flow with some restrictions - In the range of stable flow, but the 

presence of other users in the traffic stream begins to be noticeable. Freedom to 

select desired speeds is relatively unaffected, but there is a slight decline in the 

freedom to maneuver within the traffic stream from LOS A. The level of comfort 

and convenience provided is somewhat less than at LOS A, because the presence 

of others in the traffic stream begins to affect individual behavior. 

e. LOS C: Stable flow, maneuverability and speed are more restricted - In the range 

of stable flow, but marks the beginning of the range of flow in which the 

operation of individual users becomes significantly affected by interactions with 

others in the traffic stream. The selection of speed is now affected by the 

presence of others, and maneuvering within the traffic stream requires substantial 

vigilance on the part of the user. The general level of comfort and convenience 

declines noticeably at this level. 

f. LOS D: Unstable flow - temporary restrictions substantially slow driver - Highdensity, but stable flow. Speed and freedom to maneuver are severely restricted, 

and the driver or pedestrian experiences a generally poor level of comfort and 

convenience. Small increases in traffic flow will generally cause operational 

problems at this level. 

g. LOS E: Flow is unstable, vehicles are unable to pass, temporary stoppages, etc. - 

Operating conditions at or near the capacity level. All speeds are reduced to a 

low, but relatively uniform value. Freedom to maneuver within the traffic stream 

is extremely difficult, and it is generally accomplished by forcing a vehicle or 

pedestrian to "give way" to accommodate such maneuvers. Comfort and 

convenience levels are extremely poor, and driver or pedestrian frustration is 

generally high. Operations at this level are usually unstable, because small 

increases in flow or minor perturbations within the traffic stream will cause 

breakdowns. 

h. LOS F: Forced traffic flow, low speeds, traffic volumes below capacity - Forced 

or breakdown flow. This condition exists wherever the amount of traffic 

approaching a point exceeds the amount which can traverse the point. Queues 

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form behind such locations. Operations within the queue are characterized by 

stop-and-go waves, and they are extremely unstable. Vehicles may progress at 

reasonable speeds for several hundred feet or more then be required to stop in a 

cyclic fashion. LOS F is used to describe the operating conditions within the 

queue, as well as the point of the breakdown. It should be noted, however, that in 

many cases operating conditions of vehicles or pedestrians discharged from the 

queue may be quite good. Nevertheless, it is the point at which arrival flow 

exceeds discharge flow, which causes the queue to form, and LOS F is an 

appropriate designation for such points. 

i. Unable to determine 

Page 5 of Question Annotation 

52. LVPresent: Is there a lead vehicle traveling in the same lane at start of 6-second 

baseline? 

a. Yes 

b. No (Skip to Page (6) 

c. Unable to determine 

53. LVObjectID (text): What is the object ID of the lead vehicle reported by the radar at 

start of 6-second baseline? 

o If there is a lead vehicle reported by the radar, enter the Object ID 

o If radar data is not available, enter “N/A” 

o If unsure, enter “Unable to determine” 

54. LVActualRange (text): What is the X-Range to the lead vehicle reported by the 

radar at start of 6-second baseline? 

o If there is a lead vehicle reported by the radar, enter the X_Range 

o If radar data is not available, enter “N/A” 

o If unsure, enter “Unable to determine” 

55. LVEstRange: Estimate the range to the lead vehicle at start of 6-second baseline: 

a. Far (Greater than 40 m or 3 standard lane markings away) 

b. Medium (Between 12 and 40 m or 1-3 standard lane markings away) 

c. Close (Less than 12 m or 1 standard lane marking away) 

d. Unable to determine 

e. N/A (No lead vehicle) 

Lead Vehicle Range Estimate Diagrams 

***Standard lane markings are 10 ft. long, and the distance between each one is 30 ft. Thus, 

from the start of one standard marking to the start of the next is 40 feet or about 12 meters. Nonstandard lane markings (such as during a merge or delineating a turn lane) have different 

measurements and cannot be used in this manner. 

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Close (Less than 14 m on radar, or just over one standard lane marking) 

Medium (14 to 40 m on radar or 1-3 standard lane markings) 

Far (Greater than 40 m on radar or more than 3 standard lane markings) 

56. LVActualRate (text): What is the relative X-velocity of the lead vehicle reported by 

the radar at start of 6-second baseline? 

o If there is a lead vehicle reported by the radar, enter the X_Velocity 

o If radar data is not available, enter “N/A” 

o If unsure, Enter “Unable to determine” 

57. LVEstRate: Estimate the closing rate to the lead vehicle at start of 6-second baseline: 

a. Distance Rapidly Increasing 

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b. Distance Increasing 

c. Distance Constant 

d. Distance Closing 

e. Distance Rapidly Closing 

f. Unable to determine 

g. N/A (No lead vehicle) 

Page 6 of Question Annotation 

58. SVLaneChange: Does the subject driver CHOOSE to change lanes during the 10-

second time interval (10,000 timestamps) CENTERED on the start of 6-second 

baseline? This 10-second time interval includes 4 seconds (4,000 timestamps) after the 

baseline ends. The beginning and ending of this time interval are provided for you 

in Columns J and K (light red) of the Excel log.

a. No - driver does not change lanes, OR any lane change performed is forced by 

lane closure, merging requirements, or turn lane movements 

b. Yes, planned lane change – driver changes lanes based on a choice to travel in a 

different lane. This does NOT include when the driver makes required merges 

(such as merging onto/off of a highway, moving into a turn lane, or lanes 

ending/beginning – all of which should be answered “No”). 

c. Yes, evasive/unplanned lane change – driver changes lanes in order to avoid an 

accident, or an animal/object/pedestrian in the forward roadway 

d. Unable to determine 

59. SVTurnSignal: If driver changes lanes as above, does he/she use the turn signal? 

a. Driver does not change lanes 

b. Yes 

c. No 

d. Unable to determine 

60. RVPresent: Is there a trailing rear vehicle traveling in the same lane as the driver at 

start of 6-second baseline? 

a. Yes 

b. No (Skip to Page 7) 

c. Unable to determine 

61. RVEstRange: Estimate the range to the rear vehicle at start of 6-second baseline: 

a. Far (Greater than 40 m or 3 standard lane markings away) 

b. Medium (Between 12 m and 40 m or 1 to 3 standard lane markings away) 

c. Close (Less than 12 m or 1 standard lane marking away) 

d. Unable to determine 

e. N/A (No rear vehicle) 

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Rear Vehicle Range Estimate Diagrams 

***Standard lane markings are 10 ft. long, and the distance between each one is 30 ft. Thus, 

from the start of one standard marking to the start of the next is 40 feet or about 12 meters. Nonstandard lane markings (such as during a merge or delineating a turn lane) have different 

measurements and cannot be used in this manner. 

Close (Less than14 m or just over one standard lane marking) 

Medium (14 to 40 m or 1-3 standard lane markings) 

 

Far (Greater than 40 m away or more than 3 standard lane markings) 

62. RVEstRate: Estimate the closing rate of the rear trailing vehicle at start of 6-second 

baseline: 

a. Distance Rapidly Increasing 

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b. Distance Increasing 

c. Distance Constant 

d. Distance Closing 

e. Distance Rapidly Closing 

f. Unable to determine 

g. N/A (No rear vehicle) 

63. RVLaneChange: Does the rear trailing vehicle change lanes to pass the subject 

vehicle within 10 seconds (or 10,000 timestamps) starting at start of 6-second 

baseline? This 10-second time interval includes 4 seconds (4,000 timestamps) after the 

baseline ends. The beginning and ending of this time interval are provided for you 

in Columns H and I (light red) of the Excel log.

a. Yes, Rear Vehicle Moves to Pass (PLANNED) – Rear vehicle changes lanes 

based on a choice to travel in a different lane or in order to drive at a faster speed 

than the subject. This does NOT include when the rear vehicle makes required 

merges (such as merging onto/off of a highway, moving into a turn lane, or lanes 

ending/beginning – all of which should be answered “No”). 

b. Yes, Rear Vehicle Moves to Pass (EVASIVE) - rear vehicle changes lanes in 

order to avoid an accident, or an animal/object/pedestrian 

c. No – rear vehicle does not change lanes, OR any lane change performed is forced 

by lane closure, merging requirements, or turn lane movements 

d. Unable to determine 

e. N/A (No rear vehicle) 

Page 7 of Question Annotation 

64. RelationToJunction: Relation to junction at start of 6-second baseline: 

w. Non-junction – Subject vehicle is not close to a junction (the area formed by the 

connection of two roadways) 

x. Intersection – Subject vehicle is at or within 1 car length (~20 feet) of an 

intersection (roads cross at the same grade) 

y. Intersection-related – Subject vehicle is within 3 car lengths (~60 feet) of an 

intersection (where roads cross at the same grade), either approaching or exiting 

the intersection 

z. Interchange area – Subject vehicle is within the boundaries of an interchange with 

exit and/or entrance ramps present (a road junction that typically utilizes grade 

separation and one or more ramps to permit traffic on at least one road to pass 

through the junction without crossing any other traffic stream) 

aa. Entrance ramp – Subject vehicle is on or entering/exiting an entrance ramp (a 

transition roadway connecting two roadways or used for entering through-traffic 

lanes) 

bb. Exit ramp – Subject vehicle is on or entering/exiting an exit ramp (a transition 

roadway connecting two roadways or used for exiting through-traffic lanes) 

cc. Driveway, alley access, etc. – Subject vehicle is on or entering/exiting a driveway, 

alley, or some other roadway providing access to property adjacent to the traffic 

way 

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dd. Rail grade crossing – Subject vehicle is close to the at-grade connection of a 

railroad bed and roadway 

ee. Parking lot – subject vehicle is within the boundaries of a parking lot 

ff. Other – subject vehicle is related to a junction in a manner not described in other 

categories. This includes tunnels, toll booths, and bridges 

gg. Unable to determine 

65. TrafficControlDevice: Traffic control device (if any) in effect at start of 6-second 

baseline: 

gg. No traffic control - There is no traffic control applicable to the subject vehicle at 

the time of the event 

hh. Traffic signal - A traffic signal (by colors or flashing) is controlling some aspect 

of the traffic flow applicable to the subject vehicle 

ii. Stop sign 

jj. Yield sign 

kk. Construction signs/warnings 

ll. Slow or warning sign, other 

mm. School-zone related sign 

nn. Officer or watchman/traffic guard 

oo. Traffic lanes marked - There are markings on the road that contain information or 

warnings applicable to the driving task for the subject vehicle (use if NO other 

types of devices/signs are used to convey the same information). Does not 

include Railroad crossings (see below). 

pp. No passing signs 

qq. One-way road or street 

rr. Railroad crossing with markings or signs - A railroad crossing with associated 

signage (including markings on the road, signs, cross bucks) is controlling some 

aspect of traffic flow applicable to the subject vehicle 

ss. Railroad crossing with signals - A railroad crossing with associated signals 

(including flashing lights, traffic lights) is controlling some aspect of traffic flow 

applicable to the subject vehicle 

tt. Railroad crossing with gate and signals - A railroad crossing with associated 

gate(s) with or without signals (including flashing lights, traffic lights) is 

controlling some aspect of traffic flow applicable to the subject vehicle 

uu. Other - There is some type of traffic control device, not described in previous 

categories, controlling some aspect of traffic flow applicable to the subject vehicle 

vv. Unable to determine 

Page 8 of Question Annotation 

66. IntersectionPresent: What is the first type of intersection entered within 10 seconds 

(or 10,000 timestamps) starting at start of 6-second baseline? This 10-second time 

interval includes 4 seconds (4,000 timestamps) after the baseline ends. The beginning 

and ending of this time interval are provided for you in Columns H and I (light red) 

of the Excel log. 

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m. No Intersection Entered – Skip to Page 9 – if this option is selected, SKIP to 

question 36 on page 9 of the question annotation 

n. Signalized – subject’s path through intersection is controlled by a stoplight only 

o. Stop sign – subject’s path through intersection is controlled by a stop sign only 

p. Yield sign – subject’s path through intersection is controlled by a yield sign only 

q. Uncontrolled – subject’s path through intersection is not controlled by any means 

(no signs nor stoplights) 

r. Unable to determine 

67. IntersectionScan1: For the intersection coded above, does the driver appropriately 

scan for traffic PRIOR to entering the intersection? Proper scanning consists of 

gazing to roadway junctions and NOT driveways, alleyways, or parking lot entrances. 

For a 4-way intersection, a glance to the left and right is required; for a right 3-way 

intersection, a glance to the right is required; for a left 3-way intersection, a glance to the 

left is required, etc. These glances are required regardless of traffic control status (traffic 

light color, etc.). 

i. Yes, driver scans appropriately 

j. No, driver does not scan 

k. Unable to determine 

l. N/A - No intersection entered 

68. IntersectionViolate: What stopping behavior is exhibited at the intersection coded 

above? (use the unit converter to convert to miles per hour)

o. Stop not required 

p. Proper stop performed 

q. Rolling stop (minimum speed <15 mph, but greater than 0) 

r. Complete stop, but past the stop bar/sign AND in path of cross traffic 

s. No stop when stop required (minimum speed is >=15mph) 

t. Unable to determine 

u. N/A - No intersection entered 

69. IntersectionScan2: If the driver stops as first in queue at a light at the intersection 

coded above, does he/she scan within 6 seconds (or 6,000 timestamps) before the 

vehicle starts moving? Proper scanning consists of gazing to roadway junctions and 

NOT driveways, alleyways, or parking lot entrances. For a 4-way intersection, a glance 

to the left and right is required; for a right 3-way intersection, a glance to the right is 

required; for a left 3-way intersection, a glance to the left is required, etc. These glances 

are required regardless of traffic control status (traffic light color, etc.).

n. N/A, driver does not stop (skip to Page 9) 

o. N/A, driver stops, but not first in queue at light (skip to Page 9) 

p. Yes, driver scans before moving 

q. No, driver does not scan before moving 

r. Unable to determine 

s. N/A - No intersection entered (skip to Page 9) 

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49. IntersectionPhone: If SV was stopped at intersection as in above question, did subject 

complete all complex cell phone subtasks before the vehicle started moving. 

f. N/A, Cell phone use does not occur while vehicle is stopped. 

g. N/A, Cell phone use while stopped is limited to Holding/wearing or Talking only 

h. No, Complex cell phone subtasks (other than holding/wearing/talking) continue 

after vehicle starts moving 

i. Yes, all complex cell phone subtask(s) completed before vehicle starts moving. 

j. Unsure 

Page 9 of Question Annotation 

50. NumLaneBust (text): Number of unintentional lane busts occurring during this event 

– enter the total number of unintentional lane busts that occur during the entire event. Do 

NOT count intentional lane busts (such as when the driver must swerve to avoid an 

accident or an animal/object/pedestrian in the road, etc.). If there are no unintentional 

lane busts, enter “0” and skip to Page 10. 

51. BeginLaneBust1 (text): Begin timestamp of FIRST lane bust – enter the timestamp of 

the beginning of the first lane that occurs during this event. The timestamp can be found 

in the Collection Navigator at the lower, right-hand side of Hawkeye. 

52. BeginLaneBust2 (text): Begin timestamp of SECOND lane bust – enter the timestamp 

of the beginning of the second lane that occurs during this event. 

 

53. BeginLaneBust3 (text): Begin timestamp of THIRD lane bust – enter the timestamp of 

the beginning of the first third bust that occurs during this event. 

Page 10 of Question Annotation 

54. SecondaryTask1: Secondary Task 1 – Indicate any secondary tasks (up to (3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

55. SecondaryTask2: Secondary Task 2 – Indicate any secondary tasks (up to (3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

56. SecondaryTask3: Secondary Task 3 – Indicate any secondary tasks (up to (3) that the 

driver engages in during the length of the event. If more than 3 secondary tasks are 

observed, list the 3 most severe/most distracting tasks. Secondary tasks to record are 

provided in the chart below.

57. SecondaryTaskDesc (textbox): Define/Describe OTHER tasks above – For any 

secondary tasks listed as “other,” “unknown,” “other device,” “reaching for object: 

other,” or “holding object: other” above, provide a description. Also use this space to 

further explain anything unusual about the list distractions.

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58. BothHandsOff: If cell phone use is listed above, does the driver take both hands off 

the steering wheel during the cell phone task(s) that occur within the 6-second 

window? 

d. N/A - No cell use listed above 

e. No, at least one hand is on the wheel for all cell use 

f. Yes, both hands off wheel at least once during cell use 

Secondary Task Description 

No Secondary Task There are no observable signs of driver distraction 

Lost in thought 

Driver performs multiple non-specific eye glances within 6-second 

period of time (not focusing on objects of glances), or appears to be in a 

daze resulting in potential conflict. 

Looked but did not see 

Driver is looking right at (or looks at) where incident occurs, but shows 

no reaction. Often seen when blind spot is checked, but vehicles present 

are not seen. 

Cell Hand-Held: 

Locate/Reach/Answer When the driver looks for or reaches towards his/her hand-held cell 

phone or manipulates it to answer a call. 

Cell Hand-Held: 

Talk/Listen/Voice 

Commands 

When a driver is talking on a hand-held phone or has the phone up to 

his/her ear as if listening to a phone conversation or waiting for a person 

they are calling to pick up the phone. 

NOTE: If the driver uses the speaker phone function on a hand-held cell 

phone: Code as “HH: Talk/Listen/Voice Commands” if the driver keeps 

the hand-held phone in his/her hand(s) while using the speaker phone 

function. Code as “PHF: Talk/Listen/Voice Commands” if the driver 

puts the phone down (thus, does NOT hold it in his/her hand(s)) while 

using the speaker phone function. 

Cell Hand-Held: Dialing When the driver is pressing buttons or interacting with a touch screen on 

a hand-held cell phone in order to dial a phone number to make a call. 

This can include dialing, searching for a contact’s number, entering a 

voice mail password, etc. 

NOTE: This does NOT include pressing a button to 

answer a call (coded as “HH: Locating/Reaching/ 

Answering”) or pressing a button to end a call 

(coded as “HH: End Task”). 

NOTE: Additionally, “HH: Dialing” does NOT include pressing 

buttons or interacting with a touch screen in order to type/read a text 

message (which should be coded as “HH: Text messaging” if driver 

Final Report 

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types or “HH: Viewing/Browsing/Reading” if driver reads) or browse 

the Internet/use phone applications (which should be coded as “HH: 

Viewing/Browsing/Reading”).
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

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Secondary Task Description 

Cell Hand-Held: Text 

messaging 

When a driver is pushing buttons or interacting with a touch screen on a 

hand-held cell phone in order to type a text message. 

NOTE: This does not include reading a text message, which should be 

coded as “HH: Viewing/Browsing/Reading.” 

Cell Hand-Held: 

Viewing/Browsing/Reading 

When the driver views the hand-held cell phone display with or without 

pressing buttons or manipulating the touch screen for a purpose other 

than making/receiving a call or sending a text message. Examples 

include: when the driver uses the cell phone to check time, read a 

received text message, browse the Internet or email, or use the phone’s 

other applications. 

NOTE: If any viewing and/or button manipulation is seen and there is 

NO record of a call being made/received/ended or a text being sent, then 

use this category. Reading a received text message would be coded 

using this category. 

NOTE: Exceptions to this rule: #1 - When a call is ending, code as “HH: 

End Task” if the driver looks at the phone and/or presses a button to end 

a call. #2 - When a call is being answered, any glances or associated 

button presses should be coded as “HH: Locate/Reach/Answer.” 

Cell Hand-Held: Holding When the driver holds a hand-held cell phone in his/her hand but does 

not interact with it. It does NOT count as holding if the phone is resting 

on the driver’s seat (next to or between legs), or on the driver’s lap (both 

of which would end the cell phone interaction and be coded as no cell 

phone task). 

NOTE (The 5-Second Rule): If the subject is viewing, dialing, or 

performing another task with a hand-held phone, then holds the phone 

without visually or manually interacting with it for at least 5,000 

consecutive timestamps (or 5 consecutive seconds), this “break” period 

should be coded as “HH: Holding.” If the driver resumes another (or the 

same) subtask before the 5-consecutive-second period ends, do NOT 

code “HH: Holding.” Rather, continue to code as the initial task until a 

new task begins. 

NOTE: Holding is assumed in all other hand-held subtasks (“HH:...”) 

and does not need to be coded simultaneously with any other hand-held 

task. However, if the phone is being held during any Portable Hands 

Free (PHF) or Integrated Hands Free (IHF) tasks, then “HH: Holding” 

would need to be simultaneously coded. 

Cell Hand-Held: End Task When the driver completes a specific cell phone objective by either 

pressing a button to end the call, putting the phone down after ending a 

call or text, or flipping/sliding the phone closed after ending a call or 

text. 

Cell Integrated Hands-Free: 

Press Button to 

Begin/Answer 

When the driver presses a button on the steering wheel or center stack in 

order to begin a cell phone interaction. This can include pushing to 

answer a call, pushing to voice dial, or pushing to enter a voice 

command. 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

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Secondary Task Description 

When the driver presses the button on the steering wheel or center stack 

in order to begin the cell phone interaction. 

Cell Integrated Hands-Free: 

Talk/Listen/Voice 

Commands 

When a driver talks, listens, or gives voice commands on an integrated 

device. Driver must be observed talking repeatedly with no obvious 

passenger interaction. Additionally, this option should only be used 

when the cell records indicate that the driver has made or received a call 

on an integrated hands-free device. 

Cell Integrated Hands-Free: 

Press button to end When the driver presses the button on the steering wheel or center stack 

in order to end the cell phone interaction. 

Cell Portable Hands-Free: 

Locate/Put-on 

Headset/Earpiece 

When the driver looks for or reaches towards a headset or earpiece. If 

more than one task occurs (e.g., driver looks for earpiece, reaches for it 

and then puts it in his ear), the first frame number would be the start of 

the first task (reaching for earpiece) and the last frame number coded 

would be the end of the last task (i.e., placing earpiece in ear.) 

Cell Portable Hands-Free: 

Holding/Wearing 

Headset/Earpiece 

When a driver is holding a headset/earpiece in his/her hand or wearing it 

on his/her head but not interacting with it (and not involved in a phone 

conversation). Also code as “PHF: Hold/Wearing” if the driver has been 

holding the earpiece/headset in his/her hand(s) for some time and finally 

moves to put it on. It does NOT count as holding if the headset/earpiece 

is resting on the driver’s seat (next to or between legs), or on the driver’s 

lap.

NOTE: If the subject is talking/listening on a 

portable hands-free device or performing another 

task with a hand-held phone or portable hands-free 

device, then holds the headset/earpiece in hand or 

on his/her head without interacting for at least 

5,000 timestamps (or 5 consecutive seconds), this 

“break” period should be coded as “PHF: 

Hold/Wear Headset/Earpiece.” If the driver 

resumes another task before the 5,000-consecutivetimestamp period ends, do NOT code “PHF: 

Hold/Wear Headset/Earpiece.” 

NOTE: While coding PHF: Talk/Listen, do NOT intersperse PHF: 

Hold/Wear unless is it clear that a phone call has ended. The driver may 

stop talking for periods of time (including breaks longer than 5 seconds) 

to listen to the conversation. This should be coded straight through as 

PHF: Talk/Listen. 

NOTE: Holding/wearing headset or earpiece is assumed in all other 

Portable Hands Free (“PHF:...”) subtasks and does not need to be coded 

simultaneously with any other PHF task. However, if a headset/earpiece 

is being held or worn during any Hand-Held (HH) or Integrated Hands 

Free (IHF) tasks, then “PHF: Holding/Wearing” would need to be 

simultaneously coded. 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

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Secondary Task Description 

Cell Portable Hands-Free: 

Push Button to 

Begin/Answer 

When the driver presses a button on the headset/earpiece in order to 

begin a cell phone interaction. This can include pushing to answer a call 

or pushing to give a voice command to make a call. This button may be 

located on the headset/earpiece itself, or occasionally somewhere on the 

wire connecting the device to the phone.

NOTE: If instead of pushing a button on the 

headset/earpiece to answer or make a call, the 

driver pushes a button or dials on a hand-held 

phone, this would be coded as “HH: Dialing” or 

“HH: Locate/Reach/Answer,” even if the 

subsequent conversation takes place via a Portable 

Hands Free device.

Cell Portable Hands-Free: 

Talk/Listen/Voice 

Commands 

When a driver is talking on a headset, earpiece, or other aftermarket 

device, OR listening to a phone conversation, OR waiting for a person 

they are calling to pick up the phone. Driver must be observed talking 

repeatedly with no obvious passenger interaction to conclude that the 

headset/earpiece is in use. 

NOTE: This subtask should be coded if the talking 

subtask is performed on a portable hands-free 

device, even if the dialing, answering, or callending subtasks are performed using a hand-held 

phone.

NOTE: If the driver uses the speaker phone function on a hand-held cell 

phone: Code as “Hand-held: Talk/Listen/Voice Commands” if the driver 

keeps the hand-held phone in his/her hand(s) while using the speaker 

phone function. Code as “Portable Hands-Free: Talk/Listen/Voice 

Commands” if the driver puts the phone down (thus, does NOT hold it in 

his/her hand(s)) while using the speaker phone function. 

Cell Portable Hands-Free: 

Push Button to End 

When the driver presses the button on the headset/ear piece in order to 

end the cell phone interaction. This button may be located on the 

headset/earpiece itself, or occasionally somewhere on the wire 

connecting the device to the phone.

NOTE: If instead of pushing a button on the headset/earpiece to end a 

call, the driver pushes a button on a hand-held phone, this would be 

coded as “HH: End Task,” even if the conversation took place via a 

Portable Hands Free device. 

Cell Phone Navigation When the driver is using the navigation feature of a hand-held cell 

phone. It is not entirely clear what this will look like, but it may occur 

when the phone is in a cradle on the dash, or when the driver is clearly 

using the phone for turn-by-turn navigation purposes.

NOTE: Please note this interaction in the Comments section of Excel 

log so that a closer examination can be performed.
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

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Secondary Task Description 

Cell Other Cell Phone Task When a driver is interacting with a hand-held cell phone, portable handsfree device, or integrated hands-free device in some manner not 

described in previous categories. This includes, but is not limited to, the 

following: 

 When the driver plugs a hand-held phone into a power charger. 

 When the subject is playing with a hand-held phone or portable 

hands-free device, or fiddling with them without any purposeful 

manipulation. 

 When the subject puts a hand-held cell phone into a case after 

holding it in his/her hand for 5 or more consecutive seconds 

(5,000 + consecutive timestamps) after other HH tasks have 

ended. Includes reaching for the separate case, maneuvering 

phone into the case, and then putting it down or holding it 

(coded as holding if longer than 5 seconds, or 5,000 consecutive 

timestamps). 

NOTE: If subject must remove a hand-held cell phone from the case 

before using it, code as “HH: Locating/Reaching/Answering.” If the 

subject is putting the phone back INTO case immediately following a 

call or text, code it as “HH: End Task.” If the subject is putting the phone 

back INTO a case after “HH: Holding,” code as “Other Cell Phone 

Task.” 

NOTE: Define the observed behaviors in the Comments section of 

Excel log. 

Talking/singing/dancing 

(w/o passenger or cell) 

Driver is moving lips as if in conversation or singing a song. Also use if 

driver is moving his/her arms, head, or other body part in time with the 

beat of music 

Mark this if driver is talking or singing or dancing and there is no 

obvious passenger component (either passenger is clearly not present or 

the driver is not looking in the direction of a passenger seat and does not 

turn head as if communicating with someone). 

Reading/Writing 

Driver is reading or writing on material that is in the vehicle, but not a 

part of the vehicle (i.e., not reading external signs, or radio display). 

This could be reading or writing on directions, paper material, 

packaging. If reading a phone number, record as dialing cell phone. 

Cognitive, other 

Driver is emotionally upset or angry, or engaged in another activity not 

included in other categories, that requires the driver to obviously be 

thinking about something other than driving 

Details about condition or emotional state should be specified in the 

appropriate questions. 

Interacting with passenger 

A passenger is visible or not visible, but the driver is clearly interacting 

with a passenger in either the adjacent or rear seat. This could be talking, 

listening, reacting to (e.g., laughing), moving toward or away from the 

passenger (i.e., reaching for the passenger, or avoiding a pat from the 

person). 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

Final Report 

175 

Secondary Task Description 

Moving object in vehicle 

An object inside the vehicle is in motion and causes the driver to look 

away from the driving task, either due to the motion of the vehicle or due 

to another passenger throwing the object. (Ex. object fell off seat when 

driver stopped hard at a traffic light) 

Insect in vehicle Interaction with any insect in the vehicle (e.g., swatting at insect, moving 

body to avoid insect, looking around trying to locate insect) 

Pet in vehicle 

Any interaction with pet, including petting, talking to, or moving pet or 

interacting with pet carrier. 

Only code if animal/pet is visible at some point in the trip file or if there 

is history/context with the driver and the driver is exhibiting behaviors 

that are appropriate to having a pet in the vehicle 

Object dropped by driver 

Driver is holding something and it drops and the driver then picks it back 

up 

This category supersedes other "reaching" categories in the situation of 

an object being dropped and immediately retrieved 

Reaching for object, other 

Driver reaches for an object not described in any other category. Once 

the driver has finished reaching for the object and has it in hand (if not 

being moved for intended usage), then it becomes "object in vehicle, 

other," as long as it doesn't fit into any of the other categories (e.g., 

eating, drinking, etc.) 

Holding object, other 

Driver is holding an object not described in other categories. Could be 

food, drink, pen, paper, etc. Must continue for at least 5 seconds without 

other manipulations. If less than 5 seconds, code as previous task (e.g., 

reaching for object, personal hygiene). 

Object in vehicle, other 

Driver clearly is looking at, handling, or manipulating an object (visible 

or not) or thing located in the vehicle, other than those listed in other 

categories 

Operating other electronic 

device 

Driver is manipulating some non-manufacturer-installed electronic 

device (PDA, laptop, mp3 player, etc.) either by pressing buttons, 

viewing, opening/closing, plugging in, etc. Reaching for this object 

should be coded as "Reaching for object, other" 

Adjusting radio or HVAC 

Driver interacts with climate control or radio either by touching the 

buttons on the center stack, dashboard, or steering wheel, or glancing at 

the controls. Includes inserting/retrieving CDs and adjusting vents. 

Adjusting/monitoring other 

devices integral to vehicle 

Driver interacts with a manufacturer-installed device other than those 

listed in other categories, either by touching or glancing at the device. 

Includes interaction with seat belt, door locks, sun visor, etc. Does NOT 

include interacting with driving-critical tasks such as turn signal, 

headlights, gear shift, and windshield wipers. 

Looking at non-drivingrelated external 

object/event 

Driver is looking outside of the vehicle in the direction of what is 

obviously an object or incident that is not related to the driving task. 

May include looking at an accident, aspects of construction sites/zones, 

animals/pedestrians that are not in or entering the path of travel. 

Only mark if it is clear that the driver is tracking a specific external 

distraction as they drive by. Other non-specific or driving-related glances 

should be coded as "Driving related inattention to forward roadway" 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

Final Report 

176 

Secondary Task Description 

Eating/drinking 

Driver has food or drink that will be put in his/her mouth with or without 

the use of a utensil. If driver is chewing (except gum) also code as 

Eating/drinking. If driver is simply holding food or drink for 5 or more 

seconds, code as Holding Object: Other 

Smoking/tobacco 

Lighting, smoking, or extinguishing cigar or cigarette. Also includes use 

of chewing tobacco or holding a lit cigarette. Reaching for tobacco 

products should be coded "Reaching for object: other" 

Personal hygiene 

Includes applying make-up (including lotion/chapstick), checking self in 

mirror, purposefully fixing/brushing hair, shaving, tweezing, 

brushing/flossing teeth, putting on/removing/adjusting jewelry (including 

watches), putting on/removing/adjusting contacts or glasses. Reaching 

for hygiene-related items should be coded as "Reaching for object: 

other.” 

Does not include swiping hair from eyes or quick/thoughtless 

rubbing/scratching, twirling hair. 

Driving-related inattention 

to forward roadway 

Driver glances away from the direction of travel out a window or at a 

side or center mirror for a driving-related issue (i.e., changing lanes, 

crossing through an intersection). Exception: if the vehicle is backing 

and the driver is looking out of the left window to see the road in the 

direction of travel, this is not coded as a distraction. 

Other Secondary Task 

(define in Text box) 

Driver is looking in a location other than the direction of travel, in a 

manner not listed in other categories. 

Unknown 

Can't tell or make a judgment whether there is a distraction 

Ex. Part of the video is missing or there is insufficient information in the 

video to make a determination 

Page 11 of Question Annotation 

59.DriverExpectation: If an external incident occurs within the 6-second 

window, describe the driver’s reaction to it: An external incident is 

anything unexpected or out of the ordinary that presents a safety hazard.

m. No external event occurs 

n. Fully expects, drives appropriately/reacts in a timely manner 

o. Somewhat caught off guard, but quickly reacts in appropriate manner 

p. Very much caught off guard, has a delayed reaction (~ > 0.75 s or 750 

timestamps) 

q. Extremely caught off guard, does not react at all 

r. Unable to determine 

60.Emotion: Prior to any external incident noted above, rate the driver’s 

emotional state during the 6-second window: 

o. Neutral/No Emotion Shown 

p. Happy 

q. Angry/Frustrated/Impatient 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

Final Report 

177 

r. Sad 

s. Surprised 

t. Other (Could Be Concerned/Opinionated/Apologetic/Guilt/Contempt) 

u. Unable to Determine 

Driver Emotion Reaction Definitions 

Emotion Operational Definition 

Unable to Determine  Cannot tell what emotion the driver is showing 

Neutral/No Emotion Shown  The driver has a straight face, does not smile or laugh, does not gesture 

Happy  The driver smiles or laughs 

 The driver gestures in excitement 

Angry/Frustrated 

 The driver lowers/squeezes eyebrows, wrinkling forehead 

 The driver clenches his/her teeth 

 The driver yells (opens mouth wide with eyebrows lowered) 

 The driver gestures in anger/frustration 

 The driver raises his/her upper lip or tightens lips 

Sad 

 The driver has droopy eyebrows (raises inner eyebrows, lowers outer 

eyebrows) 

 The driver frowns by lowering the outer corners of his/her lips 

Surprised 

 The driver’s eyebrows raise 

 The driver’s mouth opens 

 The driver gestures 

Other  Emotional reaction that does not fit into any other category 

 Please define in the Notes section on the Excel Log 

61.EmotionIntensity: Prior to any external incident noted above, rate the 

intensity of the driver’s emotional state during the 6-second window: 

k. Neutral/No Emotion Shown 

l. Slight (Emotion Somewhat Shown) 

m. Marked or Pronounced (Emotion Very Much Shown) 

n. Severe (Emotion Extremely Shown) 

o. Unable to determine 

Driver Emotional Intensity Reduction Definitions 

Intensity of Emotion Operational Definition 

Unable to Determine  Cannot tell the intensity of the emotion 

Neutral/No Emotion Shown 

 The driver has a straight face, does not smile or laugh, 

does not gesture 

 Note, will always be selected if Neutral/No Emotion is 

selected above 
 Appendix A.9 Driver, Vehicle, and 

Environmental Questions for SCE Baselines 

Final Report 

178 

Intensity of Emotion Operational Definition 

Slight (Emotion Somewhat Shown)  The driver no longer has a straight face 

 However, no gesturing or head movement is observed 

Marked or Pronounced (Emotion Very 

Much Shown) 

 The driver no longer has a straight face 

 The driver gestures one time in a reserved manner 

 The driver moves his head one time 

Severe (Emotion Extremely Shown) 

 The driver has wide eyes and a wide open mouth 

 The driver is screaming 

 The driver gestures wildly, or the driver moves his head 

frequently 

62.RaterSurprise As the analyst, how surprised/shocked/interested were you 

by the video captured during this event? 

k. No heightened level of surprise/shock/interest 

l. Somewhat surprised/shocked/interested 

m. Very much surprised/shocked/interested 

n. Extremely surprised/shocked/interested 

o. Unable to determine 

63.NoteComments (text): General Notes/Comments – include descriptions of 

any instances where you coded “Unable to determine” or “Other” in the 

questions above. As well as notes about any other circumstances that help to 

explain your responses and/or better define the conditions and occurrences 

of this event. Other notes you should type in include (but are not limited to) 

when the driver gets out of the vehicle during an event and particularly 

extreme weather conditions.
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

179 

A.10 Investigation of Drivers’ Cell Phone Use 

A.10.1 Duration of Calls and Text Messages by Cell Phone Type 

The duration of the sampled phone interaction for call and text samples was tested across cell 

phone types using a series of Kruskal-Wallis tests. Below are the results for the follow-up tests 

comparing two cell phone types or text messaging/browsing at a time. All comparisons were 

found significant, except portable hands-free and integrated hands-free phone interactions when 

driving below 8 km/h.

Table 41. Results of Kruskal-Wallis Tests on Duration Between Phone Types 

Comparison 

Above 8 

km/h 

χ2

Above 8 

km/h 

p value 

Below 8 

km/h 

χ2

Below 8 

km/h 

p value 

Hand-Held Versus Portable Hands-Free 35.6 < .0001 8.9 .0028 

Hand-Held Versus Integrated Hands-Free 4.0 .0453 6.9 .0084 

Hand-Held Versus Text/Browse 180.9 < .0001 75.9 < .0001 

Portable Hands-Free Versus Integrated HandsFree 14.5 .0001 0.9 .3421 

Portable Hands-Free Versus Text/Browse 179.0 < .0001 46.4 < .0001 

Integrated Hands-Free Versus Text/Browse 149 < .0001 67.6 < .0001 
Appendix A.10 Investigation o

Descriptive statistics for cell phone subtasks performed above 8 km/h are presented in Table 42. Results from infperformed on subtask durations are presented in the following section. 

Table 42. Descriptive Statistics for Cell Phone Subtask Durations 

Cell Phone Type Cell Phone Subtask N Mean (s) SE Max (s) Min (s) 25th Percentile (s) 50th Percentile (s) 

Per

Hand-Held HH: Talk/Listen 525 178.7 12.1 2045 0.9 35.3 68.5 Hand-Held HH: Dial 309 12.4 0.5 64.8 0.6 6.5 10.3 Hand-Held HH: Browse/Read, HH: Talk/Listen 133 4.4 0.8 68 0.3 1 1.6 Hand-Held HH: Locate/Answer 331 4.3 0.2 20.3 0.5 2.3 3.5 Hand-Held HH: End Task 461 4 0.1 21.2 0.1 1.9 3.3 Portable Hands-Free PHF: Talk/Listen 156 297.7 27 1733.5 0.8 59.8 173.6 Portable Hands-Free PHF: Locate/Put On 15 12 2.8 39.8 0.1 6.3 8.7 Portable Hands-Free HH: Dial 29 10.4 1.2 27.8 2.3 5.6 8.5 Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 35 4.1 0.8 17.4 0.5 1 2.7 Portable Hands-Free HH: Locate/Answer 43 3.6 0.5 21.1 0.1 1.7 2.7 Portable Hands-Free PHF: End Task 33 3 0.5 16.4 0.6 1.6 2.2 Portable Hands-Free PHF: Begin/Answer 13 2.9 1.1 15.3 0.4 0.9 1.2 Integrated Hands-Free IHF: Talk/Listen 237 226.8 21.6 2425.6 2.9 47.4 87.0 Integrated Hands-Free HH: Dial 67 12.9 1.3 47.4 1.5 5.5 9.5 Integrated Hands-Free 

HH: Browse/Read, IHF: Talk/Listen 31 6.8 1 28.8 0.5 4 4.8 

Integrated Hands-Free IHF: Begin/Answer 120 4.6 0.6 37.6 0.5 1.6 2.6 Integrated Hands-Free HH: Locate/Answer 72 3.9 0.4 15.3 0.1 2 2.7 Integrated Hands-Free IHF: End Task 154 2.9 0.2 10 0.1 1.3 2.3 Text/Browse HH: Text 207 34.6 2.5 302.2 0.7 11.8 23.7 

Final Report 

180 
Appendix A.10 Investigation o

Final Report 

181 

Cell Phone Type Cell Phone Subtask N Mean (s) SE Max (s) Min (s) 25th Percentile (s) 50th Percentile (s) 

Per

Text/Browse HH: Browse/Read 286 13.7 0.9 87.4 0.7 4.7 9.4 Text/Browse HH: Locate/Answer 301 3.1 0.1 19.5 0.1 1.8 2.5 Text/Browse HH: End Task 352 2 0.1 24.2 0.1 0.9 1.4 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

182 

A.10.2 Frequency and Duration Talk/Listen Subtask 

The count and average duration in seconds with standard error is listed for the talk/listen subtask 

across cell phone types by speed level in Table 43. Only talk/listen subtasks with a valid speed 

measure were included. 

Table 43. Frequency and Average Duration of Talk/Listen Subtask Across Cell Phone 

Types by Speed Level 

Speed Level Cell Phone Type N 

Mean 

Duration 

(s) 

SE 25th

Percentile 

75th

Percentile 

85th

Percentile 

Above 8 km/h Hand-Held 525 178.7 12.1 35.3 184.9 328.1 

Above 8 km/h Portable Hands-Free 156 297.7 27.0 59.8 387.9 609.5 

Above 8 km/h Integrated Hands-Free 237 226.8 21.6 47.4 241.7 410.1 

Below 8 km/h Hand-Held 260 124.0 10.4 32.1 136.0 229.2 

Below 8 km/h Portable Hands-Free 60 302.6 56.8 38.0 432.2 683.5 

Below 8 km/h Integrated Hands-Free 97 221.3 32.4 49.0 258.6 394.8 

Table 44. Results of ANOVA for Log Duration of Talk/Listen Subtask for Driving Speed 

Above 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 2 50.3 25.1 16.2 <.0001 

Error 915 1418.7 1.6 

Corrected Total 917 1469.0 

Table 45. Results of ANOVA for Log Duration of Locate/Answer or Locate/Put on Subtask 

for Driving Speed Below 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 2 24.3 12.2 8.3 0.0003 

Error 414 604.1 1.5 

Corrected Total 416 628.4 

Table 46. Confidence Intervals (95%) for Difference Between Log Means of Duration of 

Talk/Listen Subtask Across Cell Phone Types by Speed Level 

Speed Level Cell Phone Type 

Comparison 

Difference

Between 

Log 

Means 

95% 

Confidence 

Lower 

Limits for Log 

Task Time 

95% 

Confidence 

Upper 

Limits for Log 

Task Time 

Above 8 km/h HH: Talk/Listen Versus IHF: 

Talk/Listen* 

-0.2693 -0.4980 -0.0405 

Above 8 km/h HH: Talk/Listen Versus PHF: 

Talk/Listen* 

-0.6287 -0.8953 -0.3622 

Above 8 km/h PHF: Talk/Listen Versus IHF: 

Talk/Listen* 

0.3594 0.0581 0.6608 

Below 8 km/h HH: Talk/Listen Versus IHF: 

Talk/Listen* 

-0.5063 -0.8444 -0.1683 

Below 8 km/h HH: Talk/Listen Versus PHF: 

Talk/Listen* 

-0.4855 -0.8925 -0.0786 

Below 8 km/h PHF: Talk/Listen Versus IHF: 

Talk/Listen 

-0.0208 -0.4875 0.4459 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

183 

A.10.3 Frequency and Duration of Subtasks 

For the sampled cell phone calls and text messages, observed cell-phone-related subtasks were 

noted by reductionists. The frequency and duration of the following subtasks were calculated 

across cell phone types by speed level: (1) locate/answer or locate/put on, (2) hand-held dialing 

or portable hands-free/integrated hands-free begin/answer, (3) browse/read during talk/listen, and 

(4) end task. In Table 47, the frequency and average duration of the locate/answer or locate/put 

on subtask is displayed. The results of the ANOVA on the log transformation of task time for the 

subtask are shown in Table 48 (speed above 8 km/h) and Table 49 (speed below 8 km/h). 

Following, in Table 50, are confidence intervals for the difference in duration for the subtask 

when compared across two cell phone types at a time. If the confidence interval did not contain 

zero, the difference was considered statistically significant. 

Table 47. Frequency and Average Duration of Locate/Answer or Locate/Put on Subtask 

Across Cell Phone Types by Speed Level 

Speed Level Cell Phone Type N 

Mean 

Duration

(s) 

SE 

Duration 

Above 8 km/h Hand-Held 331 4.3 331 

Above 8 km/h Integrated Hands-Free 72 3.9 72 

Above 8 km/h Portable Hands-Free 43 3.6 43 

Above 8 km/h Text/Browse 301 3.1 301 

Below 8 km/h Hand-Held 191 4.7 191 

Below 8 km/h Integrated Hands-Free 45 4.0 45 

Below 8 km/h Portable Hands-Free 27 4.2 27 

Below 8 km/h Text/Browse 168 3.2 168 

Table 48. Results of ANOVA for Log Duration of Locate/Answer or Locate/Put on Subtask 

for Driving Speed Above 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 3 15.3 5.1 12.0 <.0001 

Error 743 316.3 0.4 

Corrected Total 746 331.6 

Table 49. Results of ANOVA for Log Duration of Locate/Answer or Locate/Put on Subtask 

for Driving Speed Below 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 3 6.3 2.1 3.7 0.0112 

Error 427 238.1 0.6 

Corrected Total 430 244.3 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

184 

Table 50. Confidence Intervals (95%) for Difference Between Log Means for 

Locate/Answer or Locate/Put on Subtask Across Cell Phone Types by Speed Level 

Speed Level Cell Phone Type 

Comparison 

Difference

Between 

Log Means 

95% 

Confidence 

Lower 

Limits for Log 

Task Time 

95% 

Confidence 

Upper 

Limits for 

Log Task 

Time 

Above 8 km/h Hand-Held Versus Portable Hands-Free* 0.2851 0.0128 0.5574 

Above 8 km/h Hand-Held Versus Integrated Hands-Free 0.1630 -0.0555 0.3814 

Above 8 km/h Hand-Held Versus Text/Browse* 0.3036 0.1698 0.4374 

Above 8 km/h Portable Hands-Free Versus Integrated HandsFree -0.1221 -0.4459 0.2016 

Above 8 km/h Portable Hands-Free Versus Text/Browse 0.0185 -0.2554 0.2923 

Above 8 km/h Integrated Hands-Free Versus Text/Browse 0.1406 -0.0798 0.3610 

Below 8 km/h Hand-Held Versus Portable Hands-Free 0.0933 -0.3027 0.4892 

Below 8 km/h Hand-Held Versus Integrated Hands-Free 0.1818 -0.1373 0.5001 

Below 8 km/h Hand-Held Versus Text/Browse* 0.2610 0.0573 0.4647 

Below 8 km/h Portable Hands-Free Versus Integrated HandsFree 0.0885 -0.3803 0.5574 

Below 8 km/h Portable Hands-Free Versus Text/Browse 0.1677 -0.2316 0.5670 

Below 8 km/h Integrated Hands-Free Versus Text/Browse 0.0792 -0.2441 0.4024 

In Table 51, the frequency and average duration of the dialing or begin/answer subtask is 

displayed. The results of the ANOVA on the log transformation of task time for the subtask are 

shown in Table 52 (speed above 8 km/h) and Table 53 (speed below 8 km/h). Following, in 

Table 54, are confidence intervals for the difference in duration for the subtask when compared 

across two cell phone types at a time. If the confidence interval did not contain zero, the 

difference was considered statistically significant. 

Table 51. Frequency and Average Duration of Hand-Held Dialing or Portable HandsFree/Integrated Hands-Free Begin/Answer Subtask Across Cell Phone Types by Speed 

Level 

Speed Level Subtask N 

Mean 

Duration

(s) 

SE 

Duration 

Above 8 km/h HH: Dial 309 12.4 0.5 

Above 8 km/h IHF: Begin/Answer 120 4.6 0.6 

Above 8 km/h PHF: Begin/Answer 13 2.9 1.0 

Below 8 km/h HH: Dial 201 15.9 0.9 

Below 8 km/h IHF: Begin/Answer 45 6.8 1.0 

Below 8 km/h PHF: Begin/Answer 3 0.7 2.3 

Table 52. Results of ANOVA for Log Duration of Hand-Held Dialing or Portable HandsFree/Integrated Hands-Free Begin/Answer Subtask for Driving Speed Above 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 2 148.3 74.1 119.5 <.0001 

Error 439 272.2 0.6 

Corrected Total 441 420.5 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

185 

Table 53. Results of ANOVA for Log Duration of Hand-Held Dialing or Portable HandsFree/Integrated Hands-Free Begin/Answer Subtask for Driving Speed Below 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 2 67.2 33.6 50.6 <.0001 

Error 246 163.4 0.7 

Corrected Total 248 230.6 

Table 54. Confidence Intervals (95%) for Difference Between Log Means of Duration of 

Hand-Held Dialing or Portable Hands-Free/Integrated Hands-Free Begin/Answer Subtask 

Across Cell Phone Types by Speed Level 

Speed Level Cell Phone Type 

Comparison 

Difference

Between 

Log 

Means 

95% 

Confidence 

Lower 

Limits for Log 

Task Time 

95% 

Confidence 

Upper 

Limits for Log 

Task Time 

Above 8 km/h HH: Dial Versus IHF: Begin/Answer* 1.1898 0.9906 1.3890 

Above 8 km/h HH: Dial Versus PHF: Begin/Answer* 1.7656 1.2413 2.2900 

Above 8 km/h PHF: Begin/Answer Versus IHF: 

Begin/Answer* 

-0.5759 -1.1166 -0.0351 

Below 8 km/h HH: Dial Versus IHF: Begin/Answer* 1.0044 0.6874 1.3213 

Below 8 km/h HH: Dial Versus PHF: Begin/Answer* 3.3705 2.2527 4.4884 

Below 8 km/h PHF: Begin/Answer Versus IHF: 

Begin/Answer* 

-2.3662 -3.5122 -1.2202 

In Table 55, the frequency and average duration of the browsing/reading while talking/listening 

subtask is displayed. The results of the ANOVA on the log transformation of task time for the 

subtask are shown in Table 56 (speed above 8 km/h) and Table 57 (speed below 8 km/h). 

Following, in Table 58, are confidence intervals for the difference in duration for the subtask 

when compared across two cell phone types at a time. If the confidence interval did not contain 

zero, the difference was considered statistically significant. 

Table 55. Frequency and Average Duration of Browse/Read While Talking/Listening 

Subtask Across Cell Phone Types by Speed Level 

Speed Level Subtask N Mean (s) SE 

Above 8 km/h HH: Browse/Read, HH: Talk/Listen 133 4.4 0.8 

Above 8 km/h HH: Browse/Read, IHF: Talk/Listen 31 6.8 1.0 

Above 8 km/h HH: Browse/Read, PHF: Talk/Listen 35 4.1 0.8 

Below 8 km/h HH: Browse/Read, HH: Talk/Listen 53 5.0 0.8 

Below 8 km/h HH: Browse/Read, IHF: Talk/Listen 23 12.2 3.1 

Below 8 km/h HH: Browse/Read, PHF: Talk/Listen 15 6.2 1.5 

Table 56. Results of ANOVA for Duration of Browse/Read While Talking/Listening 

Subtask for Driving Speed Above 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 2 18.7 9.4 8.54 0.0003 

Error 196 214.6 1.1 

Corrected Total 198 233.3 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Table 57. Results of ANOVA for Duration of Browse/Read While Talking/Listening 

Subtask for Driving Speed Below 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 2 11.3 5.6 5.4 0.0064 

Error 88 92.7 1.1 

Corrected Total 90 104 

Table 58. Confidence Intervals (95%) for Difference Between Log Means of Duration of 

Browse/Read While Talking/Listening Subtask Across Cell Phone Types by Speed Level 

Speed Level Cell Phone Type 

Comparison 

Difference

Between 

Log 

Means 

95% Confidence 

Lower Limits for 

Log Task Time 

95% Confidence 

Upper Limits for 

Log Task Time 

Above 8 

km/h 

IHF: Talk/Listen Versus PHF: 

Talk/Listen* 0.6854 0.0760 1.2949 

Above 8 

km/h 

IHF: Talk/Listen Versus HH: 

Talk/Listen* 0.8625 0.3697 1.3553 

Above 8 

km/h 

PHF: Talk/Listen Versus HH: 

Talk/Listen -0.1771 -0.2924 0.6465 

Below 8 

km/h 

IHF: Talk/Listen Versus PHF: 

Talk/Listen 0.6276 -0.1844 1.4396 

Below 8 

km/h 

IHF: Talk/Listen Versus HH: 

Talk/Listen* 0.8377 0.2268 1.4486 

Below 8 

km/h 

PHF: Talk/Listen Versus HHF: 

Talk/Listen 0.2101 -0.5054 0.9257 

In Table 59, the frequency and average duration of the browsing/reading while talking/listening 

subtask is displayed. The results of the ANOVA on the log transformation of task time for the 

subtask are shown in Table 60 (speed above 8 km/h) and Table 61 (speed below 8 km/h). 

Following, in Table 62, are confidence intervals for the difference in duration for the subtask 

when compared across two cell phone types at a time. If the confidence interval did not contain 

zero, the difference was considered statistically significant. 

Table 59. Frequency and Average Duration of End Task Subtask Across Cell Phone Types 

by Speed Level 

Speed Level Cell Phone Type N Mean 

Task Time (s) 

SE 

Task Time 

Above 8 km/h Hand-Held 461 4.0 0.1 

Above 8 km/h Integrated Hands-Free 154 2.9 0.2 

Above 8 km/h Portable Hands-Free 33 3.0 0.5 

Above 8 km/h Text/Browse 352 2.0 0.1 

Below 8 km/h Hand-Held 226 3.7 0.2 

Below 8 km/h Integrated Hands-Free 47 2.6 0.2 

Below 8 km/h Portable Hands-Free 17 2.6 0.4 

Below 8 km/h Text/Browse 190 2.3 0.2 

Final Report 

186 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

187 

Table 60. Results of ANOVA for Log Duration of End Task Subtask for Driving Speed 

Above 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 3 133.0 44.3 61.0 <.0001 

Error 996 723.6 0.7 

Corrected Total 999 856.6 

Table 61. Results of ANOVA for Log Duration of End Task Subtask for Driving Speed 

Below 8 km/h 

Source df Sum of Squares Mean Square F Statistic p value 

Model 3 22.3 7.4 10.8 <.0001 

Error 394 269.6 0.7 

Corrected Total 397 291.9 

Table 62. Confidence Intervals (95%) for Difference Between Log Means of End Task 

Subtask Across Cell Phone Types by Speed Level 

Cell Phone Type 

Comparison 

Difference 

Between 

Log Means 

95% 

Confidence 

Lower Limits 

for Log Task 

Time 

95% 

Confidence 

Upper Limits 

for Log Task 

Time 

Hand-Held Versus Portable Hands-Free 0.2616 -0.1337 0.6569 

Hand-Held Versus Integrated Hands-Free* 0.3500 0.1459 0.5542 

Hand-Held Versus Text/Browse* 0.8155 0.6602 0.9707 

Portable Hands-Free Versus Integrated Hands-Free 0.0884 -0.3323 0.5092 

Portable Hands-Free Versus Text/Browse* 0.5539 0.1546 0.9532 

Integrated Hands-Free Versus Text/Browse* 0.4655 0.2536 0.6774 

Hand-Held Versus Portable Hands-Free 0.1792 -0.3552 0.7137 

Hand-Held Versus Integrated Hands-Free 0.2877 -0.0530 0.6284 

Hand-Held Versus Text/Browse* 0.4999 0.2908 0.7091 

Portable Hands-Free Versus Integrated Hands-Free 0.1085 -0.4930 0.7099 

Portable Hands-Free Versus Text/Browse 0.3207 -0.2173 0.8587 

Integrated Hands-Free Versus Text/Browse 0.2123 -0.1340 0.5585 

A.10.4 Frequency of Non-Cell Secondary Tasks 

For the sampled cell phone calls and text messages, observed non-cell-phone-related secondary 

tasks were noted by reductionists. The frequency of the following secondary tasks was calculated 

across cell phone types: adjusting radio or HVAC, eating or drinking, reading/writing, and 

adjusting/monitoring other devices integral to vehicle. In Table 63, the frequency counts of the 

subtasks with and without the secondary task “adjusting radio/HVAC” are displayed. In Table 

64, the frequency counts of the subtasks with and without the secondary task “eating or drinking” 

are displayed. In Table 65, the frequency counts of the subtasks with and without the secondary 

task “reading/writing” are displayed. In Table 66, the frequency counts of the subtasks with and 

without the secondary task “adjusting/monitoring other devices integral to vehicle” are 

displayed. 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

188 

Table 63. Frequency Counts for Secondary Task “Adjusting Radio/HVAC Observed” 

Cell Phone Type 

Adjusting the 

Radio/HVAC 

Not Observed 

Adjusting the 

Radio/HVAC 

Observed 

Total 

Hand-Held 2651 64 2715 

Integrated Hands-Free 1009 20 1029 

Portable Hands-Free 480 12 492 

Text/Browse 1920 29 1949 

Table 64. Frequency Counts for Secondary Task “Eating/Drinking” 

Cell Phone Type Eating/Drinking 

Not Observed 

Eating/Drinking 

Observed Total 

Hand-Held 2711 4 2715 

Integrated Hands-Free 1023 6 1029 

Portable Hands-Free 489 3 492 

Text/Browse 1945 4 1949 

Table 65. Frequency Counts for Secondary Task “Reading/Writing” 

Cell Phone Type Reading/Writing 

Not Observed 

Reading/Writing 

Observed Total 

Hand-Held 2702 3 2715 

Integrated Hands-Free 1022 7 1029 

Portable Hands-Free 489 3 492 

Text/Browse 1944 5 1949 

Table 66. Frequency Counts for Secondary Task “Adjusting/Monitoring Other Devices 

Integral to Vehicle” 

Cell Phone Type 

Adjusting/Monitoring Other 

Devices Integral to Vehicle 

Not Observed 

Adjusting/Monitoring Other 

Devices Integral to Vehicle 

Observed 

Total 

Hand-Held 2704 11 2715

Integrated Hands-Free 1020 9 1029

Portable Hands-Free 490 2 492

Text/Browse 1943 6 1949
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

189 

 A.10.5 Percentage of Subtasks With Both Hands Removed From 

Steering Wheel 

In sampled cell phone hand-held subtasks, reductionists recorded whether drivers had both, one, 

or no hands on the steering wheel while interacting with their cell phone. The position of a 

driver’s hands was noted for all hand-held subtasks, even if a phone interaction was portable 

hands-free or integrated hands-free (assigned because of the talk/listen subtask). The results of a 

series of Fisher’s tests investigating how the percentage of subtasks with both hands off the 

steering wheel changes across cell phone types are presented in Table 67. At both speed levels, 

hand-held phone interactions had a significantly lower percentage of subtasks with both hands 

off the steering wheel than did integrated hands-free phone interactions and text/browse 

interactions. Portable hands-free phone interactions had a significantly lower percentage of 

subtasks with both hands off the steering wheel than did integrated hands-free phone interactions 

and text/browse phone interactions when driving speed was below 8 km/h. 

Table 67. Fisher’s Exact Test Results for Percentage of Subtasks With Both Hands 

Removed From Steering Wheel Across Cell Phone Types by Speed Level 

Cell Phone Type Comparison 

Above 8 km/h 

Fisher’s Exact test 

p value 

Below 8 km/h 

Fisher’s Exact test 

p value 

Hand-Held Versus Portable Hands-Free .0983 .2972 

Hand-Held Versus Integrated Hands-Free .0024 < .0001 

Hand-Held Versus Text/Browse < .0001 < .0001 

Portable Hands-Free Versus Integrated Hands-Free .7411 .0296 

Portable Hands-Free Versus Text/Browse .6049 < .0001 

Integrated Hands-Free Versus Text/Browse 1.0000 .0777 

In Table 68, the counts and percentage of subtasks with both hands off the steering wheel are 

listed for individual subtask categories by speed level. In nearly every subtask, the percentage of 

observations with both hands off the steering wheel is higher when driving below 8 km/h than 

when driving above 8 km/h. 
Appendix A.10 Investigation o

Final Report 

190 

Table 68. Count and Percentage of Observations With Both Hands Removed From Steering Wheel A

Subtasks by Speed Level 

Cell Phone Type Subtask 

Above 8 km/h

Count 

Above 8 km/h 

Percentage With Both 

Hands Removed (%) 

Below 8 km/h

Count 

P

H

Hand-Held HH: Locate/Answer - - 1 Hand-Held HH: Dial 309 4.2 194 Hand-Held HH: Browse/Read, HH: Talk/Listen 133 0.8 50 Hand-Held HH: Talk/Listen 526 0.2 252 Hand-Held HH: End Task 1 0.0 1 Portable Hands-Free HH: Dial - - 1 Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 0 0.0 30 Portable Hands-Free PHF: Talk/Listen 34 5.9 14 Integrated Hands-Free HH: Dial 2 50.0 - Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen - - 1 Text/Browse HH: Browse/Read 67 9.0 51 Text/Browse HH: Text 30 3.3 23 Text/Browse HH: End Task 286 2.8 176 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

The results of a series of Fisher’s tests on the percentage of subtasks with both hands off the 

steering wheel during the browse/read during talking/listening subtask are listed in Table 69. 

When driving below 8 km/h, HH talk/listen and PHF-talk/listen had significantly lower 

percentages of observations of both hands off wheel than did text/browse subtasks. When driving 

below 8 km/h, IHF talk/listen had a significantly lower percentage of observations of both hands 

off wheel than did text messaging during text/browse sample. When driving below 8 km/h or 

above 8 km/h, browse/read during a text/browse sample had a significantly lower percentage of 

observations of both hands off wheel than did text messaging during text/browse sample. When 

driving above 8 km/h, HH talk/listen had a significantly lower percentage of observations of both 

hands off wheel than did text messaging during text/browse sample. 

Final Report 

191 
Appendix A.10 Investigation o

Final Report 

192 

Table 69. Fisher’s Exact Test Results for Percentage of Browse/Read During Talking/Listening Subtask 

Removed From Steering Wheel Across Cell Phone Types by Speed Level 

Browse/Read Comparison 

Above 8 km/h 

Fisher’s Exact test p value

B

Fisher

Hand-Held Talk/Listen Versus Integrated Hands-Free Talk/Listen .3352 Hand-Held Talk/Listen Versus Portable Hands-Free Talk/Listen .1057 Hand-Held Talk/Listen Versus Hand-Held Browse/Read During Text Sample .2830 Hand-Held Talk/Listen Versus Hand-Held Text During Text Sample < .0001 Portable Hands-Free Talk/Listen Versus Integrated Hands-Free Talk/Listen 1.000 Portable Hands-Free Talk/Listen Versus Hand-Held Browse/Read During Text Sample .2879 Portable Hands-Free Talk/Listen Versus Hand-Held Text During Text Sample .3912 Integrated Hands-Free Talk/Listen Versus Hand-Held Browse/Read During Text Sample .5974 Integrated Hands-Free Talk/Listen Versus Hand-Held Text During Text Sample .2205 Hand-Held Browse/Read During Text Sample Versus Hand-Held Text During Text Sample < .0001 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Final Report 

193 

A.10.6 Where Phone Was Held During Subtask 

When drivers were using a hand-held phone for any subtask, reductionists noted where the driver 

held the phone during use. For this analysis, the first hand-held phone subtask was chosen for 

each phone interaction with hand-held phone use. The phone location categories available for 

reductionists to choose from were grouped into visibility classifications. The visibility 

classifications refer to the visibility of phone use to a passing car. The visibility classifications 

included “high,” “moderate,” or “low” (Table 70). Phone use locations above the steering wheel 

or above the driver’s side window line were labeled as high visibility. Phone use locations midsteering wheel or at the driver’s side window line were labeled moderate visibility. Phone use 

locations low on the steering wheel or below the driver’s side window line were labeled low 

visibility. 

Table 70. Reduction Categories for Phone Location During Use and Corresponding 

Visibility Classification 

Phone Location During Subtask From Reduction Visibility Classification 

In both hands resting on steering wheel (high) High Visibility 

In both hands resting on steering wheel (low) Low Visibility 

In both hands resting on steering wheel (middle) Moderate Visibility 

In both hands to side of/in front of steering wheel Moderate Visibility 

In left hand against left ear High Visibility 

In one hand below steering wheel Low Visibility 

In one hand placed in front of mouth High Visibility 

In one hand resting on steering wheel (high) High Visibility 

In one hand resting on steering wheel (middle) Moderate Visibility 

In one hand to side of/in front of steering wheel Moderate Visibility 

In one hand on steering wheel (low) Low Visibility 

In one hand raised out in front of forward view High Visibility 

In one hand to side of steering wheel Moderate Visibility 

In right hand against left ear (cross body) High Visibility 

In left hand against right ear (cross body) High Visibility 

In both hands below steering wheel Low Visibility 

In right hand against right ear High Visibility 

In both hands placed in front of mouth High Visibility 

A.10.7 Where Phone Was Kept Prior to Reaching 

When a driver reached for his/her cell phone prior to use, reductionists noted the reaching 

location. The observed locations and the percentage of reaching instances are plotted in Figure 9. 

The category “Other” includes reaching onto the floor, to the instrument panel, or to the window 

visor. 
Appendix A.10 Investigation of Drivers’ Cell Phone Use 

Figure 9. Phone Reaching Locations and Observed Percentages 

A.10.8 Low and High Task Demand Analyses 

The average duration, with standard error, for all cell phone subtasks in low and high task 

demand environments is listed in Table 71. For each subtask, the difference in duration between 

low and high task demand environments was tested using a Kruskal-Wallis test. Subtasks with a 

significant difference included portable hands-free end task, integrated hands-free end task, and 

browsing/reading in a text/browse sample. 

Final Report 

194 

0%

5%

10%

15%

20%

25%

30%

35%

40%

Percentage

Reaching Locations
Appendix A.10 Investigation o

Final Report 

195 

Table 71. Cell Phone Subtask Duration in Low and High Task Demands With Significance Tes

Subtask Low Task Demand Mean Duration (s) Low Task Demand SE High Task Demand Mean Duration (s) High Task Demand SE 

Hand-Held: Locate/Answer 3.9 0.2 3.7 0.2 Hand-Held: Dialing 12.4 0.8 13.1 0.7 Hand-Held: Talk/Listen 148.5 16.6 194.7 19.4 Hand-Held: Browse/Read & Talk/Listen 5.8 2.0 4.2 0.7 Hand-Held: End Task 2.8 0.2 3.5 0.2 Portable Hands-Free: Locate/Put On 10.6 3.7 6.2 1.6 Portable Hands-Free: Begin/Answer 3.0 2.0 1.0 0.4 Portable Hands-Free: Talk/Listen 259.8 51.0 365.1 57.2 Portable Hands-Free: Browse/Read & Talk/Listen 3.7 1.0 5.6 1.6 Portable Hands-Free: End Task 4.2 1.1 2.3 0.2 Integrated Hands-Free: Begin/Answer 5.0 1.3 5.5 0.8 Integrated Hands-Free: Talk/Listen 235.0 41.1 235.5 34.5 Integrated Hands-Free: Browse/Read & Talk/Listen 7. 1.5 7.4 1.5 Integrated Hands-Free: End Task 3.1 0.3 2.4 0.2 Text/Browse: Browse/Read 17.3 2.2 12.3 2.2 Text/Browse: Text 36.8 4.2 28.6 2.5 
 Appendix A.11 Risk Rate Approach Estimation Details 

Final Report 

196 

A.11 Risk Rate Approach Estimation Details 

All data used in the risk rate estimates were above 8 km/h. 

A.11.1 Estimating Overall Talk/Listen Time 

The amount of time drivers spent talking on a cell phone while driving was estimated as follows. 

First, the difference between the call duration as specified in the cell phone records and the 

duration of the reduced talking/listening subtask was determined for each call in the sample of 

reduced cell phone calls. The average amount of time lost per call (i.e., the mean difference) was 

computed by stratifying across: 

 The original cell phone groupings that drivers were assigned when they were recruited 

(HH, PHF, and IHF) 

 The call direction (inbound, outgoing, and unknown) 

Average lost time per call = average of (cell-record-based call time – reduction based talk/listen 

time) 

Table 72 shows the mean time lost per call stratified by originally assigned cell phone grouping 

and call direction. Note: selection criteria were used to include only differences greater or equal 

to 0 and less than 2 minutes. Calls with negative differences or large positive differences were 

likely the result of multiple calls occurring within a very short time of each other. 

Table 72. Average Time Lost per Call in the Cell Phone Records Stratified by Call 

Direction and Cell Phone Type Group Drivers Were Originally Assigned 

Originally Assigned 

Group 

Mean Time Lost per 

Incoming Call (Min) 

Mean Time Lost per 

Outgoing Call (Min) 

Mean Time Lost per 

Call of Unknown 

Direction (Min) 

HH 0.583 0.418 0.483 

PHF 0.568 0.432 0.483 

IHF 0.541 0.438 0.445 

The total estimated talk time was then computed by applying the above weights to the number of 

calls made by each driver in the cell phone records. 

Total estimated talk time 

for driver i in group y = Total estimated incoming talk time + Total estimated 

outgoing talk time + Total estimated talk time for calls of 

unknown direction 

= (total records-based incoming talk time – #incoming 

calls*mean time lost per incoming call for group y) + (total 

records-based outgoing talk time - #outgoing calls*mean 

time lost per outgoing call for group y) + (total recordsbased talk time for calls of unknown direction - #calls of 

unknown direction*mean time lost per call of unknown 

direction for group y) 
 Appendix A.11 Risk Rate Approach Estimation Details 

Final Report 

197 

A.11.2 Estimating Talk/Listen Time for the Three Cell Phone Types 

The goal of this step was to estimate how much time drivers in an assigned cell phone type group 

spent talking on the various types of cell phones. This was done as follows. For each originally 

assigned cell phone type group, the total talk/listen time spent by drivers on each cell phone type 

was computed using the reduced cell phone interaction data. The proportion of time spent on 

each cell phone type was then computed for each group. The tables below present the proportion 

of time spent talking on the three types of cell phones computed by stratifying across each group 

(Table 73, Table 74, and Table 75). Note: every row sums to 1. 

Table 73. Proportion of Talk Time Spent on an HH, PHF, or IHF Cell Phone During 

Incoming Calls in the Cell Phone Records 

Originally Assigned 

Group 

Proportion of Total 

Incoming Talk Time 

on HH Cell Phone 

Proportion of Total 

Incoming Talk Time 

on IHF Cell Phone 

Proportion of Total 

Incoming Talk Time 

on PHF Cell Phone 

HH 0.835 0.012 0.153 

PHF 0.520 0.082 0.399 

IHF 0.351 0.626 0.023 

Table 74. Proportion of Talk Time Spent on an HH, PHF, or IHF Cell Phone During 

Outgoing Calls in the Cell Phone Records 

Originally Assigned 

Group 

Proportion of Total 

Outgoing Talk Time 

on HH Cell Phone 

Proportion of Total 

Outgoing Talk Time 

on IHF Cell Phone 

Proportion of Total 

Outgoing Talk Time 

on PHF Cell Phone 

HH 0.974 0.000 0.026 

PHF 0.483 0.099 0.418 

IHF 0.180 0.762 0.058 

Table 75. Proportion of Talk Time Spent on an HH, PHF, or IHF Cell Phone During Calls 

of Unknown Direction in the Cell Phone Records 

Originally Assigned 

Group 

Proportion of Total 

Unknown Direction 

Talk Time on HH 

Cell Phone 

Proportion of Total 

Unknown Direction 

Talk Time on IHF 

Cell Phone 

Proportion of Total 

Unknown Direction 

Talk Time on PHF 

Cell Phone 

HH 1.000 0.000 0.000 

PHF 0.554 0.216 0.229 

IHF 0.224 0.776 0.000 

Total estimated talk time on cell phone type x for a driver i in group y = 

Total estimated incoming call time for driver i * proportion of cell phone 

type x, incoming, group y + Total estimated outgoing call time for driver i

* proportion of cell phone type x, outgoing, group y + Total estimated 

unknown call time for driver i * proportion of cell phone type x, unknown, 

group y
 Appendix A.11 Risk Rate Approach Estimation Details 

Final Report 

198 

A.11.3 Estimating Visual-Manual Subtask Time During Calls 

The time spent performing visual-manual subtasks during a call was estimated as follows. First, 

the amount of time spent performing visual-manual subtasks for a given HH, PHF, or IHF 

interaction was computed by subtracting the reduced talk time from the overall length of the 

reduced cell phone interaction. The average visual-manual time per call was then computed by 

stratifying by the originally assigned cell phone group and the call direction. 

Table 76. Average Amount of Time Spent Performing Visual-Manual Subtasks per Call 

Originally Assigned 

Group 

Mean Visual-Manual 

Subtask Time for 

Incoming Calls (Min) 

Mean Visual-Manual 

Subtask Time for 

Outgoing Calls (Min) 

Mean Visual-Manual 

Subtask Time for 

Calls of Unknown 

Direction (Min) 

HH 0.170 0.340 0.220 

PHF 0.152 0.317 0.267 

IHF 0.112 0.251 0.288 

Total estimated time spent 

performing visual-manual 

subtasks during calls = (#incoming calls * mean visual-manual subtask 

time for incoming calls) + (#outgoing calls * mean 

visual-manual subtask time for outgoing calls) + 

(#unknown calls * mean visual-manual subtask time 

for calls of unknown direction) 

A.11.4 Estimating Visual-Manual Subtask Time During Text 

Messages 

The time spent performing visual-manual subtasks during a text message was estimated. The 

procedure used considers that there were drivers that provided text records, and drivers that did 

not provide text records. The total duration of the visual-manual subtasks performed in the 

sampled text messages was computed. The average total visual-manual subtask duration was 

then computed by stratifying by originally assigned cell phone type group and the direction of 

the text message. 

Table 77. Average Amount of Time Spent Performing Visual-Manual Subtasks per Text 

Originally Assigned 

Group 

Mean Visual-Manual 

Subtask Time for 

Incoming Text 

messages (Min) 

Mean Visual-Manual 

Subtask Time for 

Outgoing Text 

messages (Min) 

Mean Visual-Manual 

Subtask Time for Text 

messages of Unknown 

Direction (Min) 

HH 0.627 0.718 0.535 

PHF 0.819 1.046 0.000 

IHF 0.465 0.699 0.398 
 Appendix A.11 Risk Rate Approach Estimation Details 

Final Report 

199 

The estimation equation used for the drivers that provided text records is as follows: 

Total estimated time spent 

performing visual-manual 

subtasks during text messages = (# incoming text messages * mean visual-manual 

subtask time for incoming text messages) + 

(#outgoing text messages * mean visual-manual 

subtask time for outgoing text messages) + 

(#unknown text messages * mean visual-manual 

subtask time for text messages of unknown 

direction) 

The estimation equation used for the drivers that did not provide text records is as follows. First, 

the text messaging rate (as measured by duration of text messaging per driving hour) was 

computed by originally assigned cell phone group using the available text records. The text 

messaging rates were then applied to the drivers without text records. The equation is shown 

below and the text messaging rates are shown in Table 78. 

Total estimated time spent 

performing visual-manual 

subtasks during text messages = total driving hours * average time of text messaging 

per hour of driving 

Table 78. Average Text Messaging Duration by Cell Phone Group 

Originally Assigned 

Group 

Number of 

Drivers 

Total Driving Time 

Above 8 km/h (Hr) 

Total Text Time 

(Min) 

Average Text 

Messaging Duration 

per hour of driving 

(Min) 

HH 34 49997.1 777.3 0.93 

PHF 42 93662.7 3001.0 1.92 

IHF 45 83205.8 807.1 0.58 

Note that there are five drivers (three in the PHF group, two in the IHF group) with an 

extraordinarily high text messaging rate. Their rates were larger than the mean rate plus three 

standard deviations. Nevertheless, were kept in the estimates. 

A.11.5 Estimating Overall Visual-Manual Time 

The total estimated time spent performing visual-manual subtasks was computed by adding the 

total estimated visual-manual time for calls to the total estimated visual-manual time for text 

messages. 

Total estimated visual-manual time = total call-based visual-manual time + total text-based 

visual-manual time 
 Appendix A.11 Risk Rate Approach Estimation Details 

Final Report 

200 

A.11.6 Estimating the Visual-Manual Time for the Three Cell 

Phone Types 

In determining how to distribute the total visual-manual subtask time across the three cell phone 

types, the time spent performing visual-manual subtasks when text messaging was exclusively 

assigned to HH cell phone use. Next, the total time spent performing visual-manual subtasks 

during HH, PHF, and IHF calls was computed using the reduced cell phone samples (computed 

for each call as the duration of the cell phone interaction minus the duration of the talk/listen 

time). This was done separately for the drivers in each of the originally assigned cell phone type 

groups. 

The proportion of the total time spent performing visual-manual subtasks during calls was then 

determined as follows. For each group, the total visual-manual time for a call was computed for 

each type of cell phone. The proportion of time for a given cell phone type was computed by 

dividing into the total visual-manual time. Note: every row sums up to 1 when full precision 

numbers are used. 

Table 79. Proportion of Visual-Manual Time Spent on an HH, PHF, or IHF Cell Phone 

During Incoming Calls 

Originally Assigned 

Group 

Proportion of Total 

Incoming Visual-Manual 

Time on HH Cell Phone 

Proportion of Total 

Incoming Visual-Manual 

Time on IHF Cell Phone 

Proportion of Total 

Incoming Visual-Manual 

Time on PHF Cell Phone 

HH 0.911 0.004 0.085 

PHF 0.396 0.074 0.531 

IHF 0.214 0.776 0.010 

Table 80. Proportion of Visual-Manual Time Spent on an HH, PHF, or IHF Cell Phone 

During Outgoing Calls 

Originally Assigned 

Group 

Proportion of Total 

Outgoing Visual-Manual 

Time on HH Cell Phone 

Proportion of Total 

Outgoing Visual-Manual 

Time on IHF Cell Phone 

Proportion of Total 

Outgoing Visual-Manual 

Time on PHF Cell Phone 

HH 0.975 0.000 0.025 

PHF 0.577 0.024 0.399 

IHF 0.219 0.648 0.133 

Table 81. Proportion of Visual-Manual Time Spent on an HH, PHF, or IHF Cell Phone 

During Calls of Unknown Direction 

Originally Assigned 

Group 

Proportion of Total 

Unknown Direction 

Visual-Manual Time on 

HH Cell Phone 

Proportion of Total 

Unknown Direction 

Visual-Manual Time on 

IHF Cell Phone 

Proportion of Total 

Unknown Direction 

Visual-Manual Time on 

PHF Cell Phone 

HH 1.000 0.000 0.000 

PHF 0.653 0.143 0.205 

IHF 0.717 0.283 0.000 
 Appendix A.11 Risk Rate Approach Estimation Details 

Total VM time on an HH 

cell phone for a driver i in 

group y = 

Total incoming call-based VM time for driver i * 

proportion of time on HH cell phone, incoming, group y + 

Total outbound call-based VM time for driver i * 

proportion of time on HH cell phone, outgoing, group y + 

Total unknown direction call-based VM time for driver i * 

proportion of time on HH cell phone, unknown, group y 

+ Total text-based VM time for driver i

Total VM time on a PHF 

cell phone for a driver i in 

group y = 

Total incoming call-based VM time for driver i * 

proportion of time on PHF cell phone, incoming, group y + 

Total outbound call-based VM time for driver i * 

proportion of time on PHF cell phone, outgoing, group y + 

Total unknown direction call-based VM time for driver i * 

proportion of time on PHF cell phone, unknown, group y 

Total VM time on an IHF 

cell phone for a driver i in 

group y = 

Total incoming call-based VM time for driver i * 

proportion of time on IHF cell phone, incoming, group y + 

Total outbound call-based VM time for driver i * 

proportion of time on IHF cell phone, outgoing, group y + 

Total unknown direction call-based VM time for driver i * 

proportion of time on IHF cell phone, unknown, group y 

A.11.7 Estimating the Total Cell Phone Use Time 

Total Estimated cell phone use time = total estimated talk time + total estimated visual-manual 

time 

A.11.8 Estimating the Total Cell Phone Use Time for the Three Cell 

Phone Types 

Total Estimated cell phone use time on HH cell phone = total estimated talk time on HH cell 

phone + total estimated visual-manual time on HH cell phone 

Total Estimated cell phone use time on PHF cell phone = total estimated talk time on PHF cell 

phone + total estimated visual-manual time on PHF cell phone 

Final Report 

201 
 Appendix A.11 Risk Rate Approach Estimation Details 

Total Estimated cell phone use time on IHF cell phone = total estimated talk time on IHF cell 

phone + total estimated visual-manual time on IHF cell phone 

A.11.9 Estimating the Total General Driving Time 

The total estimated time spent not using a cell phone was computed as follows. 

Total estimated general driving time = total driving time – total estimated cell phone use time 

Final Report 

202 
 Appendix A.12 Driver Performance ANOVA Results 

A.12 Driver Performance ANOVA Results 

A.12.1 Percent TEORT 

Figure 10 shows the mean percent TEORT when drivers initiated various cell phone subtasks 

above 8 km/h. Figure 10, as well as the other analyses of driver performance in this appendix, 

only plot the call samples that were categorized as one of the three cell phone types or were a 

sampled text message. They also plot all the data that were available for each subtask, and are 

not graphical representations of the matched samples that were tested in the inferential tests. 

Figure 10. Drivers’ Mean Percent TEORT When Initiating a Cell Phone Subtask Above 8 

km/h 

A.12.2 TEORT Duration 

Figure 11 shows the mean TEORT duration when drivers initiated various cell phone subtasks 

above 8 km/h. 

Final Report 

203 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

204 

Figure 11. Drivers’ Mean TEORT Duration When Initiating a Cell Phone Subtask Above 8 

km/h. 

Table 82 presents the ANOVA results for the between-subjects comparisons of TEORT 

durations for subtasks that perform a similar function. Tukey-Kramer tests were performed to 

identify where the significant differences existed. 

Table 82. ANOVA Results for Between-Subject Comparisons of TEORT Durations for 

Subtasks that Perform a Similar Function 

Action Subtask 

Mean 

EORT 

Duration (s)

SE n df1 df2 F Statistic p-value 

Locate Device HH: Locate/Answer 1.5 0.1 1.5 2 169 1.84 .1624 

Locate Device HH: Locate/Answer for PHF 1.6 0.6 1.6 2 169 1.84 .1624 

Locate Device HH: Locate/Answer for IHF 2.5 0.4 2.5 2 169 1.84 .1624 

Initiate Call HH: Dial 7.8A 0.4 309 4 200 11.94 < .0001 

Initiate Call HH: Dial for PHF 6.8A 0.8 29 4 200 11.94 < .0001 

Initiate Call HH: Dial for IHF 8.3A 0.8 67 4 200 11.94 < .0001 
 Appendix A.12 Driver Performance ANOVA Results 

Action Subtask 

Mean 

EORT 

Duration (s)

SE n df1 df2 F Statistic p-value 

Initiate Call PHF: Begin/Answer 0.5B 0.2 13 4 200 11.94 < .0001 

Initiate Call IHF: Begin/Answer 2.5B 0.4 120 4 200 11.94 < .0001 

End Use HH: End Task 1.8A 0.1 461 2 191 4.18 .0166 

End Use PHF: End Task 0.5B 0.1 33 2 191 4.18 .0166 

End Use IHF: End Task 1.3A 0.1 154 2 191 4.18 .0166 

A.12.3 Speed Standard Deviation 

Figure 12 shows the mean speed standard deviation of the vehicle when drivers initiated various 

cell phone subtasks above 8 km/h. 

Figure 12. Drivers’ Mean Speed Standard Deviation When Initiating a Cell Phone Subtask 

Above 8 km/h 

Final Report 

205 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

206 

For each subtask and matched baseline sample that had a valid speed measure, a one-way withinsubject ANOVA was performed to investigate whether the mean speed standard deviation when 

initiating the subtask differed from the mean speed standard deviation during the baseline 

sample. Table 83 presents the ANOVA summary results for each test. 

Table 83. ANOVA Results for Within-Subject Comparisons of Speed Standard Deviation 

Between Each Subtask and Its Matched Baseline 

Cell Phone Type Subtask Baseline 

Mean SE Subtask Mean SE n df1 df2

F 

Statistic

p

value 

Hand-Held HH: Locate/Answer 4.81 0.29 5.05 0.32 202 1 87 0.38 .5387 

Hand-Held HH: Dial 4.75 0.36 4.61 0.42 131 1 64 3.08 .0842 

Hand-Held HH: Talk/Listen 4.79 0.28 5.09 0.33 207 1 91 0.03 .8528 

Hand-Held HH: Browse/Read, HH: Talk/Listen 3.81 0.42 4.57 0.50 56 1 34 0.82 .3706 

Hand-Held HH: End Task 4.96 0.31 6.32 0.46 179 1 84 4.50 .0368 

Portable Hands-Free PHF: Locate/Put On 4.28 0.70 3.67 0.83 4 1 2 0.68 .4950 

Portable Hands-Free PHF: Begin/Answer 6.98 3.28 7.55 3.44 8 1 5 0.00 .9654 

Portable Hands-Free HH: Locate/Answer 4.80 0.93 6.67 1.12 23 1 12 1.78 .2066 

Portable Hands-Free HH: Dial 5.75 1.53 7.06 1.72 13 1 7 0.49 .5078 

Portable Hands-Free PHF: Talk/Listen 5.01 0.84 5.95 0.80 49 1 22 0.86 .3647 

Portable Hands-Free PHF: End Task 4.63 2.09 5.84 1.80 9 1 6 0.61 .4648 

Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 3.43 1.18 5.86 1.10 16 1 12 3.30 .0945 

Integrated Hands-Free IHF: Begin/Answer 4.51 0.47 4.66 0.70 69 1 36 0.22 .6433 

Integrated Hands-Free HH: Locate/Answer 4.87 0.69 3.65 0.66 39 1 25 3.94 .0582 

Integrated Hands-Free HH: Dial 4.47 0.75 3.89 1.03 31 1 21 0.42 .5256 

Integrated Hands-Free IHF: Talk/Listen 4.29 0.38 4.60 0.53 109 1 49 0.07 .7862 

Integrated Hands-Free IHF: End Task 3.95 0.41 5.19 0.72 77 1 43 4.39 .0422 

Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 2.95 0.54 3.90 1.01 14 1 11 1.15 .3075 

Text/Browse HH: Locate/Answer 4.54 0.32 5.22 0.41 192 1 55 2.08 .1545 

Text/Browse HH: Browse/Read 4.43 0.35 4.70 0.44 157 1 47 0.01 .9320 

Text/Browse HH: Text 4.24 0.41 3.84 0.40 112 1 26 0.06 .8150 

Text/Browse HH: End Task 4.62 0.33 5.15 0.36 178 1 49 1.25 .2696 

To investigate whether changes in speed standard deviation when performing a subtask differed 

across cell phone types, speed difference scores were created by subtracting the matched baseline 

speed standard deviation from the subtask speed standard deviation. The difference scores were 

grouped by cell phone type and compared using one-way between-subjects ANOVAs. Table 84 

presents the mean speed standard deviation differences for the subtasks and their respective test 

statistics. No significant differences were found. 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

207 

Table 84. Mean Speed Standard Deviation Difference Scores for Various Subtasks Across 

Cell Phone Types 

Action Subtask Mean Difference SE n df1 df2 F Statistic p

value 

Locate Device HH: Locate/Answer 0.24 0.38 202 2 127 2.21 .1143 

Locate Device HH: Locate/Answer for PHF 1.50 1.07 27 2 127 2.21 .1143 

Locate Device HH: Locate/Answer for IHF -1.22 0.96 39 2 127 2.21 .1143 

Initiate Call HH: Dial -0.13 0.52 131 4 133 0.79 .5367 

Initiate Call HH: Dial for PHF 1.31 2.35 13 4 133 0.79 .5367 

Initiate Call HH: Dial for IHF -0.58 1.26 31 4 133 0.79 .5367 

Initiate Call PHF: Begin/Answer 0.57 4.23 8 4 133 0.79 .5367 

Initiate Call IHF: Begin/Answer 0.15 0.76 69 4 133 0.79 .5367 

Talk/Listen HH: Talk/Listen 0.31 0.39 207 2 162 0.41 .6649 

Talk/Listen PHF: Talk/Listen 0.94 1.07 49 2 162 0.41 .6649 

Talk/Listen IHF: Talk/Listen 0.32 0.56 109 2 162 0.41 .6649 

Browse and Talk HH: Browse/Read, HH: Talk/Listen 0.67 0.67 56 2 57 0.40 .6695 

Browse and Talk HH: Browse/Read, PHF: Talk/Listen 2.43 1.40 16 2 57 0.40 .6695 

Browse and Talk HH: Browse/Read, IHF: Talk/Listen 0.95 1.08 14 2 57 0.40 .6695 

End Use HH: End Task 1.35 0.55 179 2 133 0.23 .7921 

End Use PHF: End Task 1.21 1.60 9 2 133 0.23 .7921 

End Use IHF: End Task 1.24 0.77 77 2 133 0.23 .7921 

A.12.4 Headway Standard Deviation 

Figure 13 shows the mean headway standard deviation of the vehicle when drivers initiated 

various cell phone subtasks above 8 km/h. Similarly to speed standard deviation, headway 

standard deviation was computed over the first 20 s from the start of the subtask. 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

208 

Figure 13. Drivers’ Mean Headway Standard Deviation When Initiating a Cell Phone 

Subtask Above 8 km/h 

For each subtask and matched baseline sample that had a valid headway measure, a one-way 

within-subject ANOVA was performed to investigate whether the mean headway standard 

deviation when initiating the subtask differed from the mean headway standard deviation during 

the baseline sample. Table 85 presents the ANOVA summary results for each test. 

Table 85. ANOVA Results for Within-Subject Comparisons of Headway Standard 

Deviation Between Each Subtask and Its Matched Baseline 

Cell Phone Type Subtask Baseline 

Mean SE Subtask Mean SE n df1 df2

F 

Statistic

p

value 

Hand-Held HH: Locate/Answer 0.06 0.01 1.09 0.99 51 1 32 0.39 .5346 

Hand-Held HH: Dial 0.07 0.01 0.12 0.02 36 1 23 3.94 .0593 

Hand-Held HH: Talk/Listen 0.06 0.01 0.07 0.01 50 1 32 0.25 .6184 

Hand-Held HH: Browse/Read, HH: Talk/Listen 0.05 0.01 0.07 0.02 18 1 12 0.51 .4893 

Hand-Held HH: End Task 0.06 0.01 0.11 0.02 40 1 25 3.92 .0587 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

209 

Cell Phone Type Subtask Baseline 

Mean SE Subtask Mean SE n df1 df2

F 

Statistic

p

value 

Portable Hands-Free PHF: Locate/Put On 0.06 0.00 0.07 0.03 2 - - - - 

Portable Hands-Free PHF: Begin/Answer 0.52 0.40 0.09 0.03 3 - - - - 

Portable Hands-Free HH: Locate/Answer 0.03 0.01 0.09 0.03 5 - - - - 

Portable Hands-Free HH: Dial 0.03 0.02 0.08 0.03 4 - - - - 

Portable Hands-Free PHF: Talk/Listen 0.15 0.09 0.08 0.04 14 1 10 0.91 .3627 

Portable Hands-Free PHF: End Task 0.05 0.02 0.05 0.02 3 - - - - 

Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 0.15 0.10 0.11 0.06 6 - - - - 

Integrated Hands-Free IHF: Begin/Answer 0.07 0.01 0.08 0.02 16 1 12 0.47 .5060 

Integrated Hands-Free HH: Locate/Answer 0.09 0.02 0.12 0.04 15 1 11 0.55 .4754 

Integrated Hands-Free HH: Dial 0.08 0.03 0.14 0.04 10 1 8 1.70 .2291 

Integrated Hands-Free IHF: Talk/Listen 0.07 0.01 0.07 0.01 32 1 23 0.09 .7634 

Integrated Hands-Free IHF: End Task 0.09 0.02 0.09 0.03 17 1 14 0.05 .8206 

Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 0.06 0.02 0.07 0.02 8 1 6 0.53 .4955 

Text/Browse HH: Locate/Answer 0.08 0.03 0.06 0.01 34 1 23 0.65 .4273 

Text/Browse HH: Browse/Read 0.05 0.01 0.05 0.01 35 1 22 0.00 .9502 

Text/Browse HH: Text 0.08 0.02 0.06 0.02 18 1 12 2.24 .1606 

Text/Browse HH: End Task 0.08 0.03 0.09 0.02 32 1 19 0.00 .9761 

To investigate whether changes in headway standard deviation when performing a subtask 

differed across cell phone types, headway standard deviation difference scores were created by 

subtracting the matched baseline headway standard deviation from the subtask headway standard 

deviation. The difference scores were grouped by cell phone type and compared using one-way 

between-subjects ANOVAs. Table 86 presents the mean headway standard deviation differences 

for the subtasks and their respective test statistics. No significant differences were found. 

Table 86. Mean Headway Standard Deviation Difference Scores for Various Subtasks 

Across Cell Phone Types 

Action Subtask Mean Difference SE n df1 df2 F Statistic p

value 

Locate Device HH: Locate/Answer 1.03 0.99 51 2 46 0.08 .9189 

Locate Device HH: Locate/Answer for PHF 0.04 0.02 9 2 46 0.08 .9189 

Locate Device HH: Locate/Answer for IHF 0.03 0.04 15 2 46 0.08 .9189 

Initiate Call HH: Dial 0.05 0.02 36 - - - - 

Initiate Call HH: Dial for PHF 0.07 0.05 4 - - - - 

Initiate Call HH: Dial for IHF 0.06 0.06 10 - - - - 

Initiate Call PHF: Begin/Answer -0.43 0.38 3 - - - - 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

210 

Action Subtask Mean Difference SE n df1 df2 F Statistic p

value 

Initiate Call IHF: Begin/Answer 0.00 0.02 16 4 47 4.63 .0031 

Talk/Listen HH: Talk/Listen 0.01 0.01 50 2 65 2.34 .1048 

Talk/Listen PHF: Talk/Listen -0.07 0.09 14 2 65 2.34 .1048 

Talk/Listen IHF: Talk/Listen 0.00 0.01 32 2 65 2.34 .1048 

Browse and Talk HH: Browse/Read, HH: Talk/Listen 0.01 0.02 18 2 23 1.24 .3067 

Browse and Talk HH: Browse/Read, PHF: Talk/Listen -0.05 0.04 6 2 23 1.24 .3067 

Browse and Talk HH: Browse/Read, IHF: Talk/Listen 0.01 0.03 8 2 23 1.24 .3067 

End Use HH: End Task 0.05 0.02 40 2 41 1.06 .3571 

End Use PHF: End Task 0.00 0.02 3 2 41 1.06 .3571 

End Use IHF: End Task 0.01 0.04 16 2 41 1.06 .3571 

A.12.5 Unintentional Lane Bust Rate 

Figure 14 shows the mean unintentional lane bust rate when drivers initiated various cell phone 

subtasks above 8 km/h. The unintentional lane bust rate was computed as the number of 

unintentional lane busts that occurred during the sample interval divided by the duration of the 

sample interval. 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

211 

Figure 14. Drivers’ Mean Unintentional Lane Bust Rate When Performing a Cell Phone 

Subtask Above 8 km/h 

For each subtask and matched baseline sample that had a valid unintentional lane bust rate, a 

one-way within-subject ANOVA was performed to investigate whether the mean unintentional 

lane bust rate when initiating the subtask differed from the mean unintentional lane bust rate 

during the baseline sample. Table 87 presents the ANOVA summary results for each test. 

Table 87. ANOVA Results for Within-Subject Comparisons of Unintentional Lane Bust 

Rate Between Each Subtask and Its Matched Baseline 

Cell Phone Type Subtask Baseline 

Mean SE Subtask Mean SE n df1 df2

F 

Statistic

p

value 

Hand-Held HH: Locate/Answer .003 .001 0.005 0.002 202 1 87 1.62 .2065 

Hand-Held HH: Dial .005 .001 0.003 0.001 131 1 64 2.29 .1350 

Hand-Held HH: Talk/Listen .003 .001 0.001 0.000 207 1 91 5.90 .0171 

Hand-Held HH: Browse/Read, HH: 

Talk/Listen 

.005 .002 0.009 0.007 56 1 34 0.04 .8480 

Hand-Held HH: End Task .003 .001 0.004 0.003 179 1 84 0.18 .6746 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

212 

Cell Phone Type Subtask Baseline 

Mean SE Subtask Mean SE n df1 df2

F 

Statistic

p

value 

Portable Hands-Free PHF: Locate/Put On .000 .000 0.000 0.000 4 - - - - 

Portable Hands-Free PHF: Begin/Answer .000 .000 0.000 0.000 8 1 5 - - 

Portable Hands-Free HH: Locate/Answer .002 .002 0.000 0.000 23 1 12 1.38 .2627 

Portable Hands-Free HH: Dial .000 .000 0.006 0.006 13 1 7 0.75 .4146 

Portable Hands-Free PHF: Talk/Listen .003 .002 0.000 0.000 47 1 21 2.14 .1581 

Portable Hands-Free PHF: End Task .000 .000 0.000 0.000 9 1 6 - - 

Portable Hands-Free HH: Browse/Read, PHF: 

Talk/Listen 

.009 .007 0.000 0.000 16 1 12 2.12 .1714 

Integrated HandsFree IHF: Begin/Answer .003 .001 0.015 0.010 69 1 36 1.17 .2871 

Integrated HandsFree HH: Locate/Answer .001 .001 0.011 0.008 39 1 25 1.26 .2719 

Integrated HandsFree HH: Dial .000 .000 0.006 0.004 31 1 21 1.77 .1973 

Integrated HandsFree IHF: Talk/Listen .002 .001 0.000 0.000 109 1 49 3.19 .0801 

Integrated HandsFree IHF: End Task .003 .001 0.027 0.020 77 1 43 0.94 .3366 

Integrated HandsFree HH: Browse/Read, IHF: 

Talk/Listen 

.000 .000 0.000 0.000 14 1 11 - - 

Text/Browse HH: Locate/Answer .005 .001 0.009 0.005 191 1 55 0.58 .4482 

Text/Browse HH: Browse/Read .005 .001 0.005 0.002 156 1 47 0.07 .7891 

Text/Browse HH: Text .004 .001 0.005 0.002 112 1 26 0.05 .8200 

Text/Browse HH: End Task .004 .001 0.005 0.003 177 1 49 2.42 .1262 

To investigate whether changes in unintentional lane bust rate when performing a subtask 

differed across cell phone types, unintentional lane bust rate difference scores were created by 

subtracting the matched baseline unintentional lane bust rate from the subtask unintentional lane 

bust rate. The difference scores were grouped by cell phone type and compared using one-way 

between-subjects ANOVAs. Table 88 presents the mean unintentional lane bust rate differences 

for the subtasks and their respective test statistics. No significant differences were found. 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

213 

Table 88. Mean Unintentional Lane Bust Rate Difference Scores for Various Subtasks 

Across Cell Phone Types 

Action Subtask Mean Difference SE n df1 df2 F Statistic p

value 

Locate Device HH: Locate/Answer 0.001 0.002 202 2 127 0.82 .4434 

Locate Device HH: Locate/Answer for PHF -0.002 0.002 27 2 127 0.82 .4434 

Locate Device HH: Locate/Answer for IHF 0.009 0.008 39 2 127 0.82 .4434 

Initiate Call HH: Dial -0.002 0.002 131 4 133 0.99 .4131 

Initiate Call HH: Dial for PHF 0.006 0.006 13 4 133 0.99 .4131 

Initiate Call HH: Dial for IHF 0.006 0.004 31 4 133 0.99 .4131 

Initiate Call PHF: Begin/Answer 0.000 0.000 8 4 133 0.99 .4131 

Initiate Call IHF: Begin/Answer 0.012 0.009 69 4 133 0.99 .4131 

Talk/Listen HH: Talk/Listen -0.003 0.001 207 2 161 0.50 .6094 

Talk/Listen PHF: Talk/Listen -0.003 0.002 47 2 161 0.50 .6094 

Talk/Listen IHF: Talk/Listen -0.002 0.001 109 2 161 0.50 .6094 

Browse and Talk HH: Browse/Read, HH: Talk/Listen 0.005 0.006 56 2 57 1.59 .2130 

Browse and Talk HH: Browse/Read, PHF: Talk/Listen -0.009 0.007 16 2 57 1.59 .2130 

Browse and Talk HH: Browse/Read, IHF: Talk/Listen 0.000 0.000 14 2 57 1.59 .2130 

End Use HH: End Task 0.001 0.002 179 2 133 0.92 .3996 

End Use PHF: End Task 0.000 0.000 9 2 133 0.92 .3996 

End Use IHF: End Task 0.024 0.020 77 2 133 0.92 .3996 

A.12.6 Peak Deceleration 

Figure 15 shows the mean peak deceleration of the vehicle within 10 seconds of the driver 

initiating a cell phone subtask above 8 km/h. 
 Appendix A.12 Driver Performance ANOVA Results 

Figure 15. Drivers’ Mean Peak Deceleration When Initiating a Cell Phone Subtask Above 8 

km/h 

For each subtask and matched baseline sample that had a valid acceleration measure, a one-way 

within-subject ANOVA was performed to investigate whether the mean peak deceleration when 

initiating the subtask differed from the mean peak deceleration during the baseline sample. Table 

89 presents the ANOVA summary results for each test. 

Final Report 

214 
 Appendix A.12 Driver Performance ANOVA Results 

Table 89. ANOVA Results for Within-Subject Comparisons of Peak Deceleration Between 

Each Subtask and Its Matched Baseline 

Cell Phone Type Subtask Baseline 

Mean SE Subtask Mean SE n df1 df2

F 

Statistic

p

value 

Hand-Held HH: Locate/Answer 0.077 0.006 0.088 0.007 202 1 87 0.21 .6490 

Hand-Held HH: Dial 0.073 0.007 0.076 0.007 131 1 64 0.40 .5300 

Hand-Held HH: Talk/Listen 0.079 0.006 0.084 0.006 207 1 91 0.26 .6114 

Hand-Held HH: Browse/Read, HH: Talk/Listen 0.079 0.011 0.083 0.011 56 1 34 0.49 .4907 

Hand-Held HH: End Task 0.078 0.007 0.105 0.008 179 1 84 5.51 .0212 

Portable Hands-Free PHF: Locate/Put On 0.054 0.040 0.030 0.009 4 1 2 1.07 .4102 

Portable Hands-Free PHF: Begin/Answer 0.096 0.033 0.073 0.046 8 1 5 0.07 .8054 

Portable Hands-Free HH: Locate/Answer 0.102 0.018 0.110 0.016 23 1 12 0.00 .9811 

Portable Hands-Free HH: Dial 0.111 0.031 0.085 0.017 13 1 7 0.12 .7367 

Portable Hands-Free PHF: Talk/Listen 0.087 0.012 0.092 0.013 49 1 22 0.02 .8919 

Portable Hands-Free PHF: End Task 0.078 0.027 0.077 0.029 9 1 6 0.28 .6174 

Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 0.059 0.017 0.089 0.020 16 1 12 2.51 .1391 

Integrated Hands-Free IHF: Begin/Answer 0.074 0.009 0.072 0.009 69 1 36 0.05 .8287 

Integrated Hands-Free HH: Locate/Answer 0.061 0.013 0.073 0.009 39 1 25 0.21 .6513 

Integrated Hands-Free HH: Dial 0.061 0.015 0.059 0.008 31 1 21 0.22 .6448 

Integrated Hands-Free IHF: Talk/Listen 0.067 0.007 0.073 0.007 109 1 49 0.03 .8567 

Integrated Hands-Free IHF: End Task 0.067 0.008 0.076 0.009 77 1 43 0.23 .6311 

Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 0.060 0.007 0.063 0.019 14 1 11 0.04 .8468 

Text/Browse HH: Locate/Answer 0.078 0.005 0.087 0.006 192 1 55 3.27 .0759 

Text/Browse HH: Browse/Read 0.080 0.006 0.078 0.006 157 1 47 0.32 .5734 

Text/Browse HH: Text 0.078 0.006 0.072 0.007 112 1 26 0.17 .6848 

Text/Browse HH: End Task 0.078 0.005 0.079 0.007 178 1 49 0.33 .5655 

To investigate whether changes in peak deceleration when performing a subtask differed across 

cell phone types, peak deceleration difference scores were created by subtracting the matched 

baseline peak deceleration from the subtask peak deceleration. The difference scores were 

grouped by cell phone type and compared using one-way between-subjects ANOVAs. Table 90 

presents the mean peak deceleration differences for the subtasks and their respective test 

statistics. No significant differences were found. 

Final Report 

215 
 Appendix A.12 Driver Performance ANOVA Results 

Final Report 

216 

Table 90. Mean Peak Deceleration Difference Scores for Various Subtasks Across Cell 

Phone Types 

Action Subtask Mean Difference SE n df1 df2 F Statistic p

value 

Locate Device HH: Locate/Answer 0.011 0.007 202 2 127 0.07 .9312 

Locate Device HH: Locate/Answer for PHF 0.003 0.019 27 2 127 0.07 .9312 

Locate Device HH: Locate/Answer for IHF 0.012 0.015 39 2 127 0.07 .9312 

Initiate Call HH: Dial 0.003 0.009 131 4 133 0.06 .9936 

Initiate Call HH: Dial for PHF -0.026 0.031 13 4 133 0.06 .9936 

Initiate Call HH: Dial for IHF -0.002 0.015 31 4 133 0.06 .9936 

Initiate Call PHF: Begin/Answer -0.023 0.063 8 4 133 0.06 .9936 

Initiate Call IHF: Begin/Answer -0.002 0.012 69 4 133 0.06 .9936 

Talk/Listen HH: Talk/Listen -0.003 0.001 207 2 161 0.50 .6094 

Talk/Listen PHF: Talk/Listen -0.003 0.002 47 2 161 0.50 .6094 

Talk/Listen IHF: Talk/Listen -0.002 0.001 109 2 161 0.50 .6094 

Browse and Talk HH: Browse/Read, HH: Talk/Listen 0.000 0.011 56 2 57 1.29 .2831 

Browse and Talk HH: Browse/Read, PHF: Talk/Listen 0.030 0.019 16 2 57 1.29 .2831 

Browse and Talk HH: Browse/Read, IHF: Talk/Listen 0.002 0.020 14 2 57 1.29 .2831 

End Use HH: End Task 0.027 0.009 179 2 133 0.77 .4640 

End Use PHF: End Task -0.002 0.040 9 2 133 0.77 .4640 

End Use IHF: End Task 0.010 0.012 77 2 133 0.77 .4640 
 Appendix A.12 Driver Performance ANOVA Results 

A.12.7 Driver Performance When Using a Cell Phone near 

Intersections 

Figure 16 shows the percentage of subtasks in which the driver scanned before entering the 

intersection. 

Figure 16. Percentage of Cell Phone Subtask Above 8 km/h Where Driver Scanned 

Intersection 

Final Report 

217 
 Appendix A.13 Driver Adaptation ANOVA 

Results 

A.13 Driver Adaptation ANOVA Results 

A.13.1 Speed 

Figure 17 shows the mean speed of the vehicle when drivers initiated various cell phone subtasks 

above 8 km/h. 

Figure 17. Drivers’ Mean Speed When Initiating a Cell Phone Subtask Above 8 km/h 

For each subtask and matched baseline sample that had a valid speed measure, a one-way withinsubject ANOVA was performed to investigate whether the mean speed when initiating the 

subtask differed from the mean speed during the baseline sample. Table 91 presents the ANOVA 

summary results for each test. 

Final Report 

218 
 Appendix A.13 Driver A

Final Report 

219 

Table 91. ANOVA Results for Within-Subject Comparisons of Mean Speed Between Each Subtask and I

Cell Phone Type Subtask Baseline Mean SE Subtask Mean SE n df1 df2 

Sta

Hand-Held HH: Locate/Answer 69.0 2.1 69.5 2.1 202 1 87 0Hand-Held HH: Dial 70.1 2.7 72.2 2.6 131 1 64 2Hand-Held HH: Talk/Listen 68.8 2.1 67.4 2.1 207 1 91 0Hand-Held HH: Browse/Read, HH: Talk/Listen 74.4 4.2 69.6 4.3 56 1 34 1Hand-Held HH: End Task 69.6 2.3 68.2 2.3 179 1 84 0Portable Hands-Free PHF: Locate/Put On 89.0 7.5 93.3 8.5 4 1 2 0Portable Hands-Free PHF: Begin/Answer 82.2 10.1 70.2 13.6 8 1 5 1Portable Hands-Free HH: Locate/Answer 70.9 5.6 61.1 7.4 23 1 12 3Portable Hands-Free HH: Dial 73.5 6.9 68.0 9.3 13 1 7 2Portable Hands-Free PHF: Talk/Listen 74.8 4.0 68.1 4.7 49 1 22 2Portable Hands-Free PHF: End Task 80.7 10.7 68.5 11.1 9 1 6 0Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 80.2 6.5 75.5 9.3 16 1 12 0Integrated Hands-Free IHF: Begin/Answer 72.7 3.7 75.4 3.1 69 1 36 2Integrated Hands-Free HH: Locate/Answer 67.9 4.7 71.3 3.9 39 1 25 0Integrated Hands-Free HH: Dial 72.5 5.6 78.7 4.1 31 1 21 2Integrated Hands-Free IHF: Talk/Listen 74.9 2.9 75.0 2.7 109 1 49 1Integrated Hands-Free IHF: End Task 73.5 3.3 74.6 3.4 77 1 43 1Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 91.5 6.2 77.5 7.1 14 1 11 12Text/Browse HH: Locate/Answer 79.3 2.1 79.6 2.1 192 1 55 0Text/Browse HH: Browse/Read 82.5 2.3 81.8 2.2 157 1 47 1Text/Browse HH: Text 81.1 2.9 81.3 2.7 112 1 26 0Text/Browse HH: End Task 78.4 2.3 75.5 2.3 178 1 49 1
 Appendix A.13 Driver A

To investigate whether changes in speed when performing a subtask differed across cell phone types, speed diffecreated by subtracting the matched baseline speed from the subtask speed. The difference scores were grouped bcompared using one-way between-subjects ANOVAs. Table 92 presents the mean speed differences for the subtarespective test statistics. 

Table 92. Mean Speed Difference Scores for Various Subtasks Across Cell Phone Type

Action Subtask Mean Difference SE n df1 df2 F Statistic

Locate Device HH: Locate/Answer 0.5 1.3 202 2 127 1.42 Locate Device HH: Locate/Answer for PHF -7.6 4.3 27 2 127 1.42 Locate Device HH: Locate/Answer for IHF 3.4 3.7 39 2 127 1.42 Initiate Call HH: Dial 2.1 1.6 131 4 133 2.34 Initiate Call HH: Dial for PHF -5.5 4.0 13 4 133 2.34 Initiate Call HH: Dial for IHF 6.2 4.1 31 4 133 2.34 Initiate Call PHF: Begin/Answer -12.0 10.4 8 4 133 2.34 Initiate Call IHF: Begin/Answer 2.6 2.1 69 4 133 2.34 Talk/Listen HH: Talk/Listen -1.5 1.6 207 2 162 3.09 Talk/Listen PHF: Talk/Listen -6.7 4.2 49 2 162 3.09 Talk/Listen IHF: Talk/Listen 0.2 2.1 109 2 162 3.09 Browse and Talk HH: Browse/Read, HH: Talk/Listen -4.7 2.9 56 2 57 0.97 Browse and Talk HH: Browse/Read, PHF: Talk/Listen -4.7 7.1 16 2 57 0.97 Browse and Talk HH: Browse/Read, IHF: Talk/Listen -13.9 3.8 14 2 57 0.97 End Use HH: End Task -1.4 1.9 179 2 133 0.79 End Use PHF: End Task -12.2 13.7 9 2 133 0.79 End Use IHF: End Task 2.0 2.8 77 2 133 0.79 

Final Report 

220 
 Appendix A.13 Driver A

A.13.2 Headway 

Figure 18 shows the mean headway of the vehicle when drivers initiated various cell phone subtasks above 8 km

Figure 18. Drivers’ Mean Headway When Initiating a Cell Phone Subtask Above 8 km

Final Report 

221 
 Appendix A.13 Driver A

Final Report 

222 

For each subtask and matched baseline sample that had a valid headway measure, a one-way within-subject ANOto investigate whether the mean headway when initiating the subtask differed from the mean headway during the Table 93 presents the ANOVA summary results for each test. 

Table 93. ANOVA Results for Within-Subject Comparisons of Mean Headway Between Each Subtask 

Baseline 

Cell Phone Type Subtask Baseline Mean SE Subtask Mean SE n df1 df2 

Stat

Hand-Held HH: Locate/Answer 0.5 0.0 0.6 0.0 72 1 43 1Hand-Held HH: Dial 0.5 0.0 0.7 0.1 42 1 27 3Hand-Held HH: Talk/Listen 0.6 0.0 0.6 0.0 65 1 40 2Hand-Held HH: Browse/Read, HH: Talk/Listen 0.5 0.1 0.5 0.1 22 1 15 0Hand-Held HH: End Task 0.5 0.0 0.5 0.0 58 1 34 0Portable Hands-Free PHF: Locate/Put On 0.2 0.0 0.3 0.1 2 - - Portable Hands-Free PHF: Begin/Answer 0.4 0.1 0.6 0.2 3 - - Portable Hands-Free HH: Locate/Answer 0.3 0.1 0.5 0.1 9 1 4 2Portable Hands-Free HH: Dial 0.3 0.0 0.4 0.1 5 - - Portable Hands-Free PHF: Talk/Listen 0.4 0.1 0.5 0.1 18 1 12 1Portable Hands-Free PHF: End Task 0.4 0.2 0.3 0.1 3 - - Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 0.5 0.1 0.6 0.1 8 1 6 0Integrated Hands-Free IHF: Begin/Answer 0.5 0.1 0.5 0.1 23 1 18 0Integrated Hands-Free HH: Locate/Answer 0.7 0.1 0.7 0.1 19 1 14 0Integrated Hands-Free HH: Dial 0.6 0.1 0.6 0.1 14 1 11 0Integrated Hands-Free IHF: Talk/Listen 0.7 0.1 0.6 0.1 42 1 28 2Integrated Hands-Free IHF: End Task 0.6 0.1 0.6 0.1 22 1 18 0Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 0.7 0.2 0.8 0.1 10 1 8 0Text/Browse HH: Locate/Answer 0.5 0.0 0.5 0.1 62 1 33 0
 Appendix A.13 Driver A

Final Report 

223 

Cell Phone Type Subtask Baseline Mean SE Subtask Mean SE n df1 df2 

Stat

Text/Browse HH: Browse/Read 0.5 0.0 0.5 0.1 49 1 29 0Text/Browse HH: Text 0.4 0.1 0.6 0.1 29 1 15 5Text/Browse HH: End Task 0.5 0.1 0.6 0.1 52 1 27 0

To investigate whether changes in headway when performing a subtask differed across cell phone types, headwawere created by subtracting the matched baseline headway from the subtask headway. The difference scores werphone type and compared using one-way between-subjects ANOVAs. Table 94 presents the mean headway diffesubtasks and their respective test statistics. 

Table 94. Mean Headway Difference Scores for Various Subtasks Across Cell Phone Typ

Action Subtask Mean Difference SE n df1 df2 F Statistic

Locate Device HH: Locate/Answer 0.0 0.0 72 2 62 1.11 Locate Device HH: Locate/Answer for PHF 0.2 0.1 11 2 62 1.11 Locate Device HH: Locate/Answer for IHF 0.0 0.1 19 2 62 1.11 Initiate Call HH: Dial 0.1 0.1 42 - - - Initiate Call HH: Dial for PHF 0.1 0.1 5 - - - Initiate Call HH: Dial for IHF 0.0 0.1 14 - - - Initiate Call PHF: Begin/Answer 0.1 0.3 3 - - - Initiate Call IHF: Begin/Answer -77.4 6.0 26 - - - Talk/Listen HH: Talk/Listen 0.1 0.1 65 2 80 2.42 Talk/Listen PHF: Talk/Listen 0.1 0.1 18 2 80 2.42 Talk/Listen IHF: Talk/Listen -0.1 0.1 42 2 80 2.42 Browse and Talk HH: Browse/Read, HH: Talk/Listen 0.0 0.1 22 2 29 0.22 Browse and Talk HH: Browse/Read, PHF: Talk/Listen 0.1 0.1 8 2 29 0.22 Browse and Talk HH: Browse/Read, IHF: Talk/Listen 0.1 0.2 10 2 29 0.22 
 Appendix A.13 Driver A

Final Report 

224 

Action Subtask Mean Difference SE n df1 df2 F Statistic

End Use HH: End Task 0.0 0.1 58 2 54 0.37 End Use PHF: End Task -0.1 0.1 3 2 54 0.37 End Use IHF: End Task 0.0 0.1 21 2 54 0.37 

A.13.3 TTC 

Figure 19 shows the mean TTC of the vehicle when drivers initiated various cell phone subtasks above 8 km/h. 
 Appendix A.13 Driver A

Figure 19. Drivers’ Mean TTC When Initiating a Cell Phone Subtask Above 8 km/h 

For each subtask and matched baseline sample that had a valid TTC measure, a one-way within-subject ANOVA investigate whether the mean TTC when initiating the subtask differed from the mean TTC during the baseline sa

presents the ANOVA summary results for each test. 

Final Report 

225 
 Appendix A.13 Driver A

Final Report 

226 

Table 95. ANOVA Results for Within-Subject Comparisons of Mean TTC Between Each Subtask and It

Cell Phone Type Subtask Baseline Mean SE Subtask Mean SE n df1 df2 

Stat

Hand-Held HH: Locate/Answer 50.8 10.8 73.2 24.2 24 1 18 0Hand-Held HH: Dial 53.4 18.4 50.9 12.8 12 1 11 0Hand-Held HH: Talk/Listen 62.2 15.6 101.7 28.8 20 1 15 1Hand-Held HH: Browse/Read, HH: Talk/Listen 115.6 38.1 70.2 40.1 5 - - Hand-Held HH: End Task 60.0 12.2 43.5 12.4 22 1 17 0Portable Hands-Free PHF: Locate/Put On 195.2 . 18.7 - 1 - - Portable Hands-Free PHF: Begin/Answer 43.2 37.1 24.2 12.8 2 - - Portable Hands-Free HH: Locate/Answer 58.4 45.4 8.3 0.2 2 - - Portable Hands-Free HH: Dial - - - - - - - Portable Hands-Free PHF: Talk/Listen 65.0 29.5 52.3 19.7 6 - - Portable Hands-Free PHF: End Task - - - - - - - Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 61.3 27.8 22.2 8.2 4 - - Integrated Hands-Free IHF: Begin/Answer 24.9 8.4 112.4 94.3 5 - - Integrated Hands-Free HH: Locate/Answer 54.4 22.2 131.7 49.1 3 - - Integrated Hands-Free HH: Dial 12.1 8.9 83.1 47.0 2 - - Integrated Hands-Free IHF: Talk/Listen 41.5 8.2 67.6 20.8 13 1 10 2Integrated Hands-Free IHF: End Task 25.5 5.3 130.7 62.6 9 1 7 2Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 93.7 2.7 69.3 35.2 2 - - Text/Browse HH: Locate/Answer 78.0 17.7 61.7 15.3 26 1 18 0Text/Browse HH: Browse/Read 59.6 18.6 46.5 11.8 19 1 14 0Text/Browse HH: Text 56.7 17.1 74.9 28.1 6 - - Text/Browse HH: End Task 52.1 24.0 35.1 6.8 13 1 9 0
 Appendix A.13 Driver A

A.13.4 SV Lane Change Behavior 

Figure 20 shows the percentage of subtasks performed above 8 km/h where the SV was observed to change lanes interval spanning 5 seconds prior to the start of the subtask up to 5 seconds after the start of the subtask. 

Figure 20. Drivers’ Mean Headway When Initiating a Cell Phone Subtask Above 8 km

Final Report 

227 
 Appendix A.13 Driver A

Final Report 

228 

For each subtask and matched baseline sample, a McNemar Change test was performed to investigate whether th

subtasks in which the SV changed lanes differed from the proportion of baseline periods in which the SV change

presents the summary results for each test. 

Table 96. Results for Within-Subject Comparisons of SV Lane Change Behavior Between Each Subtask 

Baseline 

Cell Phone Type Subtask Baseline Percent Subtask Percent n 

χ2McNemar 

Hand-Held HH: Locate/Answer 3.96 9.90 202 6.00000 Hand-Held HH: Dial 4.58 8.40 131 1.66667 Hand-Held HH: Talk/Listen 3.38 6.28 207 2.00000 Hand-Held HH: Browse/Read, HH: Talk/Listen 1.85 1.79 56 0.00000 Hand-Held HH: End Task 3.91 2.79 179 0.33333 Portable Hands-Free PHF: Locate/Put On 0.00 0.00 4 - Portable Hands-Free PHF: Begin/Answer 12.50 12.50 8 0.00000 Portable Hands-Free HH: Locate/Answer 4.35 4.35 1 - Portable Hands-Free HH: Dial 0.00 0.00 13 . Portable Hands-Free PHF: Talk/Listen 6.12 4.08 49 0.20000 Portable Hands-Free HH: Locate/Answer 4.35 4.35 1 - Integrated Hands-Free IHF: Begin/Answer 5.80 2.90 69 1.00000 Integrated Hands-Free HH: Locate/Answer 7.69 10.26 39 0.14286 Integrated Hands-Free HH: Dial 6.45 3.23 31 0.33333 Integrated Hands-Free IHF: Talk/Listen 8.33 5.56 108 0.81818 Integrated Hands-Free IHF: End Task 8.00 3.95 76 1.00000 Text/Browse HH: Locate/Answer 5.21 7.81 192 1.08696 Text/Browse HH: Browse/Read 5.10 4.46 157 0.09091 
 Appendix A.13 Driver A

Final Report 

229 

Cell Phone Type Subtask Baseline Percent Subtask Percent n 

χ2McNemar 

Text/Browse HH: Text 3.30 5.49 91 0.66667 Text/Browse HH: End Task 4.40 1.26 159 2.77778 

To investigate whether changes in SV lane change behavior when performing a subtask differed across cell phonwere grouped into the following three categories: 

1. SV changed lanes during subtask, but not during baseline 2. SV changed lanes in both baseline and subtask, or SV did not change lanes in both baseline and subtask 3. SV changed lanes during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types using a chi-squar

presents the percentage of samples for each of the three categories and the respective chi-square p-value. 
 Appendix A.13 Driver A

Final Report 

230 

Table 97. Results for Between-Subjects Comparisons of SV Lane Change Behavior Across Cell P

Action Subtask 

SV LC During 

Subtask, but Not 

During Baseline 

Same LC 

Behavior 

During 

Baseline and 

Subtask 

SV LC During 

Baseline, but 

Not During 

Subtask 

n df 

Locate Device HH: Locate/Answer 8.91 88.12 2.97 202 Locate Device PHF: Locate/Put On 0.00 100.00 0.00 4 Locate Device HH: Locate/Answer on PHF 4.35 91.30 4.35 23 Locate Device HH: Locate/Answer on IHF 10.26 82.05 7.69 39 Initiate Call HH: Dial 7.63 88.55 3.82 131 Initiate Call HH: Dial on PHF 0.00 100.00 0.00 13 Initiate Call HH: Dial on IHF 3.23 90.32 6.45 31 Initiate Call PHF: Begin/Answer 12.50 75.00 12.50 8 Initiate Call IHF: Begin/Answer 1.45 94.20 4.35 69 Talk/Listen HH: Talk/Listen 5.80 91.30 2.90 207 Talk/Listen PHF: Talk/Listen 4.08 89.80 6.12 49 Talk/Listen IHF: Talk/Listen 3.70 89.81 6.48 108 Talk and Browse HH: Browse/Read, HH: Talk/Listen 1.79 96.43 1.79 56 Talk and Browse HH: Browse/Read, PHF: Talk/Listen 6.25 93.75 0.00 16 Talk and Browse HH: Browse/Read, IHF: Talk/Listen 0.00 92.86 7.14 14 End Use HH: End Task 1.40 96.65 1.96 358 End Use PHF: End Task 0.00 88.89 11.11 9 End Use IHF: End Task 3.95 88.16 7.89 76 
 Appendix A.13 Driver A

Final Report 

231 

A.13.5 SV Lane Position 

Figure 21 shows the percentage of subtasks performed above 8 km/h where the SV was traveling in the right-mo

the subtask. 

Figure 21. Percentage of Samples in Which Vehicle Traveled in Right-Most Lane When Initiating a Cell P

8 km/h 
 Appendix A.13 Driver A

Final Report 

232 

For each subtask and matched baseline sample, a McNemar Change test was performed to investigate whether th

subtasks in which the SV traveled in the right-most lane differed from the proportion of baseline periods in which the right-most lane. Table 98 presents the summary results for each test. 

Table 98. Results for Within-Subject Comparisons of SV Right Lane Position Between Each Subtask and 

Cell Phone Type Subtask Baseline Percent Subtask Percent n 

χ2McNemar 

Hand-Held HH: Locate/Answer 40.65 33.33 123 3.00000 Hand-Held HH: Dial 42.25 42.25 71 0.00000 Hand-Held HH: Talk/Listen 38.39 41.07 112 0.24324 Hand-Held HH: Browse/Read, HH: Talk/Listen 25.64 31.71 41 0.81818 Hand-Held HH: End Task 34.62 40.38 104 1.00000 Portable Hands-Free HH: Text, PHF: Talk/Listen 0.00 66.67 3 - Portable Hands-Free PHF: Begin/Answer 83.33 83.33 6 - Portable Hands-Free HH: Dial 55.56 44.44 9 1.00000 Portable Hands-Free PHF: Talk/Listen 37.14 34.29 35 0.14286 Portable Hands-Free PHF: End Task 28.57 28.57 7 - Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 58.33 50.00 12 1.00000 Integrated Hands-Free IHF: Begin/Answer 38.64 29.55 44 2.00000 Integrated Hands-Free HH: Locate/Answer 30.43 43.48 23 1.28571 Integrated Hands-Free HH: Dial 40.00 55.00 20 1.28571 Integrated Hands-Free IHF: Talk/Listen 37.68 37.68 69 0.00000 Integrated Hands-Free IHF: End Task 45.00 35.00 40 1.60000 Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 18.18 45.45 11 3.00000 Text/Browse HH: Locate/Answer 39.68 38.10 126 0.14286 Text/Browse HH: Browse/Read 32.35 35.29 102 0.39130 
 Appendix A.13 Driver A

Final Report 

233 

Cell Phone Type Subtask Baseline Percent Subtask Percent n 

χ2McNemar 

Text/Browse HH: Text 31.88 28.99 69 0.28571 Text/Browse HH: End Task 38.00 34.00 100 0.88889 

To investigate whether changes in SV lane position behavior when performing a subtask differed across cell pho

were grouped into the following three categories: 

1. SV in right-most lane during subtask, but not during baseline 2. SV in right-most lane for both baseline and subtask, or SV not in right-most lane for both baseline and su3. SV in right-most lane during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types using a chi-squarpresents the percentage of samples for each of the three categories and the respective chi-square p-value. 

Table 99. Results for Between-Subjects Comparisons of SV Lane Change Behavior Across Cell P

Action Subtask 

SV LC During 

Subtask, but Not 

During Baseline 

Same LC 

Behavior 

During 

Baseline 

and 

Subtask 

SV LC During 

Baseline, but Not 

During Subtask 

n df 

Locate Device HH: Locate/Answer 7.32 78.05 14.63 123 - Locate Device PHF: Locate/Put On 66.67 33.33 0.00 3 - Locate Device HH: Locate/Answer on PHF 0.00 94.12 5.88 17 - Locate Device HH: Locate/Answer on IHF 21.74 69.57 8.70 23 - Initiate Call HH: Dial 11.27 77.46 11.27 71 - Initiate Call HH: Dial on PHF 0.00 88.89 11.11 9 - Initiate Call HH: Dial on IHF 25.00 65.00 10.00 20 - Initiate Call PHF: Begin/Answer 0.00 100.00 0.00 6 - 
 Appendix A.13 Driver A

Final Report 

234 

Action Subtask 

SV LC During 

Subtask, but Not 

During Baseline 

Same LC 

Behavior 

During 

Baseline 

and 

Subtask 

SV LC During 

Baseline, but Not 

During Subtask 

n df 

Initiate Call IHF: Begin/Answer 4.55 81.82 13.64 44 - Talk/Listen HH: Talk/Listen 17.86 66.96 15.18 112 Talk/Listen PHF: Talk/Listen 8.57 80.00 11.43 35 Talk/Listen IHF: Talk/Listen 17.39 65.22 17.39 69 Talk and Browse HH: Browse/Read, HH: Talk/Listen 17.07 73.17 9.76 41 Talk and Browse HH: Browse/Read, PHF: Talk/Listen 0.00 91.67 8.33 12 Talk and Browse HH: Browse/Read, IHF: Talk/Listen 27.27 72.73 . 11 End Use HH: End Task 10.10 82.69 7.21 208 - End Use PHF: End Task 28.57 42.86 28.57 7 - End Use IHF: End Task 7.50 75.00 17.50 40 - 
 Appendix A.14 Downstream Effects from 

Drivers Using a Cell Phone 

A.14 Downstream Effects From Drivers Using a Cell 

Phone ANOVA Results 

A.14.1 Range to Rear Vehicle 

Figure 22 shows the percentage of subtasks performed above 8 km/h where the Rear Vehicle 

(RV) was rated to be traveling closely behind the SV (less than 20 m) at the start of the subtask. 

Figure 22. Percentage of Samples in Which the RV Traveled Closely Behind the SV When 

Initiating a Cell Phone Subtask Above 8 km/h 

For each subtask and matched baseline sample, a McNemar Change test was performed to 

investigate whether the proportion of subtasks in which the RV was close to the SV differed 

from the proportion of baseline periods in which the RV was close to the SV. Table 100 presents 

the ANOVA summary results for each test. 

Final Report 

235 
 Appendix A.14 Downstream Effects from 

Drivers Using a Cell Phone 

Table 100. Results for Within-Subject Comparisons of RV Tailgating Behavior Between 

Each Subtask and Its Matched Baseline 

Cell Phone Type Subtask Baseline 

Percent Subtask Percent n χ2

McNemar

pvalue 

Hand-Held HH: Locate/Answer 3.90 6.49 77 1.00000 .6250 

Hand-Held HH: Dial 6.00 6.00 50 0.00000 1.0000

Hand-Held HH: Talk/Listen 4.35 7.25 69 1.00000 .6250 

Hand-Held HH: Browse/Read, HH: Talk/Listen 0.00 30.00 20 0.81818 .5488 

Hand-Held HH: End Task 5.36 14.29 56 2.27273 .2266 

Portable Hands-Free PHF: Locate/Put On 0.00 0.00 1 - - 

Portable Hands-Free HH: Locate/Answer 0.00 10.00 10 - - 

Portable Hands-Free HH: Dial 16.67 0.00 6 - - 

Portable Hands-Free PHF: Talk/Listen 4.76 9.52 21 0.33333 1.0000

Portable Hands-Free PHF: End Task 0.00 0.00 1 - - 

Portable Hands-Free HH: Locate/Answer 25.00 25.00 4 - - 

Integrated Hands-Free HH: Locate/Answer 8.70 0.00 23 - - 

Integrated Hands-Free HH: Dial 0.00 0.00 15 - - 

Integrated Hands-Free IHF: Talk/Listen 0.00 0.00 13 - - 

Integrated Hands-Free IHF: End Task 5.56 0.00 36 - - 

Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 9.09 13.64 22 0.20000 1.0000

Text/Browse HH: Locate/Answer 9.09 7.58 66 0.14286 1.0000

Text/Browse HH: Browse/Read 12.50 7.14 56 1.28571 .4531 

Text/Browse HH: Text 10.26 10.26 39 0.00000 1.0000

Text/Browse HH: End Task 11.48 9.84 61 0.11111 1.0000

To investigate whether the likelihood of the RV traveling close to the SV when performing a 

subtask differed across cell phone types, the samples were grouped into the following three 

categories: 

1. RV traveling close to SV during subtask, but not during baseline 

2. RV traveling close to SV for both baseline and subtask, or RV not traveling close to SV 

for both baseline and subtask 

3. RV traveling close to SV during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types 

using a chi-squared test. Table 101 presents the percentage of samples for each of the three 

categories and the respective chi-square p-value. 

Final Report 

236 
 Appendix A.14 Downstream Effects from D

Final Report 

237 

Table 101. Results for Between-Subjects Comparisons of RV Tailgating Behavior Across Cell Ph

Action Subtask 

RV Close During 

Subtask, but Not 

During Baseline 

Same RV 

Distance 

During 

Baseline 

and 

Subtask 

RV Close During 

Baseline, but Not 

During Subtask 

n df 

Locate Device HH: Locate/Answer 3.90 94.81 1.30 77 Locate Device PHF: Locate/Put On 0.00 100.00 0.00 1 Locate Device HH: Locate/Answer on PHF 10.00 90.00 0.00 10 Locate Device HH: Locate/Answer on IHF 0.00 100.00 0.00 15 Initiate Call HH: Dial 4.00 92.00 4.00 50 Initiate Call HH: Dial on PHF 0.00 83.33 16.67 6 Initiate Call HH: Dial on IHF 0.00 100.00 0.00 13 Initiate Call PHF: Begin/Answer 0.00 100.00 0.00 2 Initiate Call IHF: Begin/Answer 0.00 91.30 8.70 23 Talk/Listen HH: Talk/Listen 4.35 94.20 1.45 69 Talk/Listen PHF: Talk/Listen 9.52 85.71 4.76 21 Talk/Listen IHF: Talk/Listen 0.00 94.44 5.56 36 Talk and Browse HH: Browse/Read, HH: Talk/Listen 17.07 73.17 9.76 41 Talk and Browse HH: Browse/Read, PHF: Talk/Listen 0.00 91.67 8.33 12 Talk and Browse HH: Browse/Read, IHF: Talk/Listen 27.27 72.73 0.00 11 End Use HH: End Task 7.14 90.18 2.68 112 End Use PHF: End Task 0.00 100.00 0.00 1 End Use IHF: End Task 13.64 77.27 9.09 22 
Appendix A.14 Downstream Effects from Drivers Using a Cell Phone 

A.14.2 Rear Vehicle Lane Change Behavior 

Figure 23 shows the percentage of subtasks performed above 8 km/h where the Rear Vehicle 

(RV) executed a lane change to pass the SV within 5 seconds prior to the start of the subtask up 

to 5 seconds after initiating the subtask. 

Figure 23. Percentage of Subtasks Performed Above 8 km/h Where the RV Executed a 

Lane Change to Pass the SV 

For each subtask and matched baseline sample that had a valid speed measure, a one-way withinsubject ANOVA was performed to investigate whether the mean speed when initiating the 

subtask differed from the mean speed during the baseline sample. Table 102 presents the 

ANOVA summary results for each test. 

Final Report 

238 
Appendix A.14 Downstream Effects from Drivers Using a Cell Phone 

Final Report 

239 

Table 102. Results for Within-Subject Comparisons of RV Lane Change Behavior Between 

Each Subtask and Its Matched Baseline 

Cell Phone Type Subtask Baseline 

Percent Subtask Percent n χ2

McNemar

pvalue 

Hand-Held HH: Locate/Answer 3.90 2.60 77 0.20000 1.0000

Hand-Held HH: Dial 6.00 6.00 50 0.00000 1.0000

Hand-Held HH: Talk/Listen 7.25 4.35 69 0.50000 .7266 

Hand-Held HH: Browse/Read, HH: Talk/Listen 10.53 5.00 20 1.00000 1.0000

Hand-Held HH: End Task 5.36 7.14 56 0.14286 1.0000

Portable Hands-Free PHF: Locate/Put On 0.00 0.00 2 . . 

Portable Hands-Free PHF: Begin/Answer 0.00 0.00 2 . . 

Portable Hands-Free HH: Locate/Answer 0.00 0.00 10 . . 

Portable Hands-Free HH: Dial 0.00 16.67 6 . . 

Portable Hands-Free PHF: Talk/Listen 0.00 4.76 21 . . 

Portable Hands-Free PHF: End Task 0.00 0.00 1 . . 

Portable Hands-Free HH: Browse/Read, PHF: Talk/Listen 0.00 0.00 4 . . 

Integrated Hands-Free IHF: Begin/Answer 0.00 0.00 23 . . 

Integrated Hands-Free HH: Locate/Answer 13.33 0.00 15 . . 

Integrated Hands-Free HH: Dial 23.08 0.00 13 . . 

Integrated Hands-Free IHF: Talk/Listen 8.57 0.00 35 . . 

Integrated Hands-Free IHF: End Task 18.18 4.55 22 3.00000 .2500 

Integrated Hands-Free HH: Browse/Read, IHF: Talk/Listen 9.09 0.00 11 . . 

Text/Browse HH: Locate/Answer 0.00 4.55 66 . . 

Text/Browse HH: Browse/Read 0.00 8.93 56 . . 

Text/Browse HH: Text 0.00 0.00 39 . . 

Text/Browse HH: End Task 0.00 3.28 61 . . 

To investigate whether the likelihood of the RV passing the SV when performing a subtask 

differed across cell phone types, the samples were grouped into the following three categories: 

1. RV passed the SV during subtask, but not during baseline 

2. RV passed the SV for both baseline and subtask, or RV did not pass the SV for both 

baseline and subtask 

3. RV passed the SV during baseline but not during subtask 

The distribution of samples across these three categories was compared across cell phone types 

using a chi-squared test. Table 103 presents the percentage of samples for each of the three 

categories and the respective chi-square p-value. No significant differences were found. 
Appendix A.14 Downstream Effects from D

Final Report 

240 

Table 103. Results for Between-Subjects Comparisons of RV Tailgating Behavior Across Cell Ph

Action Subtask 

RV LC During 

Subtask, but Not 

During Baseline 

Same RV 

LC 

Behavior 

During 

Baseline 

and 

Subtask 

RV LC During 

Baseline, but Not 

During Subtask 

n df 

Locate Device HH: Locate/Answer 2.60 93.51 3.90 77 Locate Device PHF: Locate/Put On 0.00 100.00 0.00 1 Locate Device HH: Locate/Answer on PHF 0.00 100.00 0.00 10 Locate Device HH: Locate/Answer on IHF 0.00 86.67 13.33 15 Initiate Call HH: Dial 6.00 88.00 6.00 50 Initiate Call HH: Dial on PHF 16.67 83.33 0.00 6 Initiate Call HH: Dial on IHF 0.00 76.92 23.08 13 Initiate Call PHF: Begin/Answer 0.00 100.00 0.00 2 Initiate Call IHF: Begin/Answer 0.00 100.00 0.00 23 Talk/Listen HH: Talk/Listen 4.35 88.41 7.25 69 Talk/Listen PHF: Talk/Listen 4.76 95.24 0.00 21 Talk/Listen IHF: Talk/Listen 0.00 91.43 8.57 35 Talk and Browse HH: Browse/Read, HH: Talk/Listen 17.07 73.17 9.76 41 Talk and Browse HH: Browse/Read, PHF: Talk/Listen 0.00 91.67 8.33 12 Talk and Browse HH: Browse/Read, IHF: Talk/Listen 27.27 72.73 0.00 11 End Use HH: End Task 3.57 93.75 2.68 112 End Use PHF: End Task 0.00 100.00 0.00 1 End Use IHF: End Task 0.00 86.36 13.64 22 
Appendix A.15 Exploratory Analyses 

Final Report 

241 

A.15 Exploratory Analyses 

A.15.1 SCE Risk Associated With Emotional Conversation 

A case-control analysis was performed to explore whether emotional conversation was 

associated with an increased risk of an SCE. For each SCE and baseline sample, reductionists 

rated the emotion and intensity of the driver during the 6-s interval (making sure only emotions 

prior to the precipitating event were coded in the SCE samples). Emotions were coded using the 

rating scales that were based off of FACS and described in the section on drivers cell phone use. 

Samples where the driver was talking on a cell phone were grouped into emotional and neutral 

conversations (pronounced and severe emotions were classified as emotional conversation, while 

neutral and slight emotions were classified as neutral conversations). The SCE risk of emotional 

conversation was first assessed relative to neutral conversation. However, only 289 samples 

(SCEs and baseline periods) existed where the driver was observed to be talking on a cell phone. 

An exact OR of 0 was computed because no SCEs had emotional conversation take place on a 

cell phone. Another analysis (i.e., a computation of an exact OR) was performed to examine the 

SCE risk of emotional conversation relative to “just driving.” However, a significant relationship 

was not found. 

Table 104. Exact Odds Ratios for the Emotional Conversation 

Subtask OR LCL UCL SCE BL SCE 

Total

BL

Total N

Emotional conversation 

relative to neutral 

conversation 

0 0 5.01 0 7 28 258 286 

Emotional conversation 

relative to “just driving” 0 0 3.74 0 7 154 1075 1229 

A.15.2 Likelihood of Scanning Intersection When Using a 

Cell Phone While Stopped 

Since all SCE and baseline samples had a minimum speed of 8 km/h, reductionists were 

instructed to indicate when the driver was stopped at an intersection (as first in cue) 6 seconds 

prior to the sample. If the driver was stopped, the reductionists looked further back to see if any 

cell phone subtasks were performed while the vehicle was stopped. They then coded whether the 

driver properly scanned the intersection prior to advancing. With these data, a Fisher’s test was 

performed to investigate whether the likelihood of scanning the intersection differed between 

using a cell phone and not using a cell phone while stopped. Although very few samples existed 

for this analysis (n = 23), drivers that performed any cell phone use while stopped were less 

likely to properly scan the intersection prior to advancing than drivers who did not use a cell 

phone while stopped (Fisher’s test p = 0.04). Too few samples were observed to assess the 

likelihood of scanning when performing visual-manual subtasks or talking subtasks. The same 

limitation prevented the assessment of SCE risk as well (no SCEs were observed 6 seconds after 

the subject vehicle was stopped). 
Appendix A.15 Exploratory Analyses 

Table 105. Frequencies of Observed Intersection Scanning 

Did Not Properly Scan Properly Scanned Total Intersection Intersection

No Cell Phone Used 2 (12.5%) 14 (87.5%) 16 

Cell Phone Used 4 (57.1%) 3 (42.86%) 7 

Total 6 17 23 

A.15.3 Drivers’ Mean Trip Time by Location 

Drivers’ mean trip time is shown in Figure 24. Drivers’ trips are binned according to the time of 

day they were performed. “AM Rush” comprises trips made between 6:00 AM and 10:00 AM. 

“Day” comprises trips made between 10:00 AM and 4:00 PM. “PM Rush” comprises trips made 

between 4:00 PM and 8:00 PM. “Night” comprises trips made between 8:00 PM and 6:00 AM.

Figure 24. Drivers’ Mean Trip Time by Location 

Final Report 

242 
DOT HS 811 757

April 2013

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