Research on the Safety Impacts of Speed 

Limiter Device Installations on Commercial 

Motor Vehicles: Phase II

March 2012
FOREWORD

The purpose of this project was to identify and assess the impacts of implementing speed limiters 

in commercial vehicle fleet operations. These impacts may be related to safety through a 

reduction in the number and/or severity of crashes, and/or address operational issues. 

This report is the second report of a two-phase approach. Phase I centered on a Detailed 

Literature Review that updated and expanded on the recent Transportation Research Board 

Synthesis Report on the Safety Impacts of Speed Limiter Device Limitations on Commercial 

Trucks and Buses. The Phase I Report was submitted to the Federal Motor Carrier Safety 

Administration in June 2009. This current study involved a series of additional tasks focused on 

a detailed research design and analysis, best practices applications, and identification of carrier, 

insurer, and enforcement official perspectives related to speed limiter implementation.

NOTICE 

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

in the interest of information exchange. The United States Government assumes no liability for 

its contents or the use thereof. 

The contents of this Report reflect the views of the contractor, who is responsible for the 

accuracy of the data presented herein. The contents do not necessarily reflect the official policy 

of the Department of Transportation. 

This Report does not constitute a standard, specification, or regulation. 

The United States Government does not endorse products or manufacturers named herein. Trade 

or manufacturers’ names appear herein only because they are considered essential to the 

objective of this document. 
Technical Report Documentation Page

1. Report No.

FMCSA-RRR-12-006

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

Research on the Safety Impacts of Speed Limiter Device Installations on 

Commercial Motor Vehicles: Phase II Draft Final Report

5. Report Date

March 2012 

6. Performing Organization Code

7. Author(s)

Richard J. Hanowski, Gene Bergoffen, Jeffrey S. Hickman, Feng Guo, 

Dan Murray, Richard Bishop, Steve Johnson, and Matthew Camden

8. Performing Organization Report No.

9. Performing Organization Name and Address

MaineWay Services

PO BOX 166

Fryeburg, ME 04037

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

BPA DTMC 75-08-A-00001

12. Sponsoring Agency Name and Address

U.S. Department of Transportation

Federal Motor Carrier Safety Administration

Office of Analysis, Research, and Technology

1200 New Jersey Ave., SE

Washington, DC 20590

13. Type of Report and Period Covered

Final Report, 

February 2009–April 2012

14. Sponsoring Agency Code

FMCSA

15. Supplementary Notes

The Contracting Officer’s Technical Representative was Albert Alvarez of the FMCSA Research Division. 

16. Abstract

The purpose of this project was to identify the impacts of implementing speed limiters (SL) in commercial vehicle 

fleet operations. These impacts may be related to safety through a reduction in the number and/or severity of 

crashes, and/or address operational issues. This report is the second report of a two-phase approach. Phase I

centered on a detailed literature review that updated and expanded on the recent Transportation Research Board’s

Synthesis Report on the Safety Impacts of Speed Limiter Device Limitations on Commercial Trucks and Buses. The 

current study involved a series of additional tasks focused on a detailed research design and analysis, a peer review 

process, evaluation of speed limiter implementation, best practices applications, and identification of carrier, 

insurer, and enforcement official perspectives related to SL implementation.

The primary safety analysis was a focus on the reduction in truck crashes that could have been avoided and/or 

mitigated with an active SL installed. This was the first study to use actual truck crash data collected directly from 

truck fleets, representing a wide array of crashes. More specifically, the study included data from 20 truck fleets, 

approximately 138,000 trucks, and analyzed more than 15,000 crashes. The findings showed strong positive benefits 

for SLs. First, in terms of safety benefits, results indicated that trucks equipped with SLs had a significantly lower 

SL-relevant crash rate (approximately 50 percent) compared to trucks without SLs. Second, the cost of the 

technology is negligible and would not be expected to be cost-prohibitive for fleets/owners. The current study went 

further than any other research previously conducted in this domain and provides important data on the efficacy of 

SLs in reducing SL-relevant crashes. 

17. Key Words

CMV, Commercial motor vehicle, commercial trucking, 

crashes, speed limiter, speed limiters

18. Distribution Statement

No restrictions

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

94

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.
SI* (MODERN METRIC) CONVERSION FACTORS

Table of APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

In Inches 25.4 Millimeters mm

Ft Feet 0.305 Meters m

Yd Yards 0.914 Meters m

Mi Miles 1.61 Kilometers km

AREA

in2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yards 0.836 square meters m2

Ac Acres 0.405 Hectares ha

mi2 square miles 2.59 square kilometers km2

VOLUME 1000 L shall be shown in m3

fl oz fluid ounces 29.57 Milliliters mL

Gal Gallons 3.785 Liters L

ft3 cubic feet 0.028 cubic meters m3

yd3 cubic yards 0.765 cubic meters m3

MASS

Oz Ounces 28.35 Grams g

Lb Pounds 0.454 Kilograms kg

T short tons (2000 lb) 0.907 megagrams (or “metric ton”) Mg (or “t”)

TEMPERATURE Temperature is in exact degrees

°F Fahrenheit 5 × (F-32) ÷ 9

or (F-32) ÷ 1.8

Celsius °C

ILLUMINATION

Fc foot-candles 10.76 Lux lx

Fl foot-Lamberts 3.426 candela/m2 cd/m2

Force and Pressure or Stress

Lbf Poundforce 4.45 Newtons N

lbf/in2 poundforce per square inch 6.89 Kilopascals kPa

Table of APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

Mm Millimeters 0.039 inches in

M Meters 3.28 feet ft

M Meters 1.09 yards yd

Km Kilometers 0.621 miles mi

AREA

mm2 square millimeters 0.0016 square inches in2

m2 square meters 10.764 square feet ft2

m2 square meters 1.195 square yards yd2

Ha Hectares 2.47 acres ac

km2 square kilometers 0.386 square miles mi2

VOLUME

mL Milliliters 0.034 fluid ounces fl oz

L Liters 0.264 gallons gal

m3 cubic meters 35.314 cubic feet ft3

m3 cubic meters 1.307 cubic yards yd3

MASS

G Grams 0.035 ounces oz

Kg Kilograms 2.202 pounds lb

Mg (or “t”) megagrams (or “metric ton”) 1.103 short tons (2000 lb) T

TEMPERATURE Temperature is in exact degrees

°C Celsius 1.8c + 32 Fahrenheit °F

ILLUMINATION

Lx Lux 0.0929 foot-candles fc

cd/m2 candela/m2 0.2919 foot-Lamberts fl

Force & Pressure Or Stress

N Newtons 0.225 poundforce lbf

kPa Kilopascals 0.145 poundforce per square inch lbf/in2

* SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380.

(Revised March 2003, Section 508-accessible version September 2009)
TABLE OF CONTENTS

LIST OF ABBREVIATIONS AND SYMBOLS ...................................................................... vii

EXECUTIVE SUMMARY ...........................................................................................................x

1. INTRODUCTION.................................................................................................................1

1.1 BACKGROUND ...........................................................................................................1

1.1.1 Speed Limiters .................................................................................................. 2

1.2 OVERVIEW OF THE CURRENT REPORT ...............................................................2

1.3 SPEED LIMITER LITERATURE REVIEW ................................................................2

1.3.1 Safety Impacts of Speed.................................................................................... 3

1.3.2 Speed Limiter Regulations .............................................................................. 11

1.3.3 Speed Limiter Technology and Usage ............................................................ 17

1.3.4 Safety Results from Implementation .............................................................. 20

1.3.5 Other Benefits Attributed to Speed Limiters .................................................. 24

1.3.6 Literature Review Summary ........................................................................... 26

1.4 EVALUATION OF SPEED LIMITER IMPLEMENTATION IN COMMERCIAL 

TRUCKING .................................................................................................................27

1.4.1 Speed Limiter Technology: Status and Availability in Heavy Trucks ........... 27

1.4.2 Speed Limiter Technology: Status and Availability in Motorcoaches ........... 30

1.4.3 Speed Limiter Usage: Scope/Operational Techniques in Heavy Vehicles ..... 30

1.4.4 Speed Limiter Usage: Scope and Operational Techniques in Motorcoaches . 32

1.4.5 Future Trends .................................................................................................. 32

1.4.6 Summary of the Evaluation of Speed Limiter Implementation in Commercial 

Trucking ...................................................................................................................... 33

2. METHODS ..........................................................................................................................35

2.1 PEER REVIEW PROCESS .........................................................................................35

2.1.1 Selection of Review Panel Participants .......................................................... 35

2.1.2 Webinar for Offsite Participants ..................................................................... 36

2.1.3 Peer Review Panel Web site to Obtain Additional Comments and 

Recommendations ....................................................................................................... 37

2.2 DATA ANALYSIS METHODS .................................................................................41

2.2.1 Research Design.............................................................................................. 41

2.2.2 Data Collection Procedures ............................................................................. 43
3. RESULTS ............................................................................................................................51

3.1 CARRIER DEMOGRAPHICS ....................................................................................51

3.1.1 Carrier Demographic and Safety Management Results .................................. 54

3.2 DESCRIPTIVE CRASH DATA..................................................................................55

3.2.1 Preliminary Crash Rate ................................................................................... 55

4. DISCUSSION ......................................................................................................................61

4.1 CONCLUSIONS FROM ANALYSES OF EFFECTIVENESS OF SPEED 

LIMITERS IN COMMERCIAL MOTOR VEHICLES ..............................................61

4.1.1 Safety Benefits of Speed Limiters .................................................................. 61

4.2 FINAL SUMMARY ....................................................................................................62

REFERENCES .............................................................................................................................69

LIST OF APPENDICES

APPENDIX A—CONTACTS MADE WITH OTHER ORGANIZATIONS ........................63

APPENDIX B—FREQUENCY OF TRUCKS WITH AN ONBOARD SAFETY SYSTEM 

BY YEAR.............................................................................................................................65

APPENDIX C—CRASH FREQUENCY BY YEAR AND CARRIER ..................................67
vi 

LIST OF FIGURES (AND FORMULAS) 

Figure 1. Chart. Average Overall Crash Rate and SL-Relevant Crash Rate in the SL and Non-SL 

Cohorts. Overall Crash Rate is Not Statistically Significant, and the SL-Relevant Crash 

Rate is Statistically Significant. ................................................................................... xvi

Figure 2. Equation. Negative Binomial Regression Model. ........................................................ xvi

Figure 3. Equation. Log(μij) in the Negative Binomial Regression Model. ................................ xvi

Figure 4. Equation. Power Model ....................................................................................................5

Figure 5. Screenshot. Webinar Conference Screen Used by Offsite Participants. ........................36

Figure 6. Screenshot. Home Page for Peer Review Panel Web Site. ............................................39

Figure 7. Screenshot. Example of Interactive Web Site Comments and Reply Area. ...................40

Figure 8. Diagram. Schematic of the Retrospective Cohort Design to be Used in the Current 

Study. ..............................................................................................................................43

Figure 9. Graph. Overall Crash Rate and SL-Relevant Crash Rate by Carrier in the Non-SL 

Cohort. ............................................................................................................................57

Figure 10. Graph. Overall Crash Rate and SL-Relevant Crash Rate by Carrier in the SL Cohort.57

Figure 11. Chart. Average Overall Crash Rate and SL-Related Crash Rate in the SL and Non-SL 

Cohorts. ..........................................................................................................................58

Figure 12. Equation. Negative Binomial Regression Model. ........................................................58

Figure 13. Equation. Log(μij) in the Negative Binomial Regression Model..................................59

Figure 14. Graph. Plot of SL Setting and SL-Relevant Crash Rate for Carriers in the SL Cohort.60

LIST OF TABLES

Table 1. Number of Crashes and Crash-Free Trucks by SL Status ............................................. xiv

Table 2. Crash Frequency and Crash Rate by SL Status ...............................................................xv

Table 3. The Mixed Effect Model Covariance Parameters Estimates ........................................ xvii

Table 4. The Effects of SL Status on the SL-Relevant Crash Rate ............................................ xvii

Table 5. Percent of Trucks Speeding by Location ...........................................................................4

Table 6. Assessment of Injury Severity Relative to Speed ..............................................................5

Table 7. Distribution of Crashes by Roadway Locations ................................................................7

Table 8. Data Regarding Speeding, Speed Limits, and Crashes ......................................................8

Table 9. Carrier Demographic and Safety Management Techniques ............................................52

Table 10. Frequency of Sector by SL Status..................................................................................55

Table 11. SafeStat SEA Scores by SL Status ................................................................................55

Table 12. Frequency of Mean Trip Length by SL Status ..............................................................55

Table 13. Number of Crashes and Crash-Free Truck-Years by SL Status ....................................55

Table 14. Crash Frequency and Crash Rate by SL Status .............................................................56

Table 15. The Mixed Effect Model Covariance Parameters Estimates .........................................59

Table 16. The Effects of SL Status on the SL-Relevant Crash Rate .............................................59

Table 17. Frequency of Trucks With an Onboard Safety System by Year....................................65

Table 18. Crash Frequency by Year and Carrier ...........................................................................67
vii 

LIST OF ABBREVIATIONS AND SYMBOLS

ANOVA Analysis of variance 

ANTC Australian National Transport Commission

ATA American Trucking Associations

ATRI American Transportation Research Institute

BAC Blood alcohol concentration

CDL Commercial driver’s license

CMV Commercial motor vehicle

CTBSSP Commercial Truck and Bus Safety Synthesis Program

CV Commercial vehicle

DTLR Department for Transportation, Local Government, and Region

ECM Electronic control module

ECMT European Conference of Ministries of Transport

EMA Engine Manufacturers Association

EPA Environmental Protection Agency

EPROM Erasable Programmable Read-Only Memory

FARS Fatality Analysis Reporting System

FHWA Federal Highway Administration

FMCSA Federal Motor Carrier Safety Administration

FOT Field operational test

GES General Estimates System

GHG Greenhouse gases

GIS Geographic Information System

GVM Gross Vehicle Mass

IIHS Insurance Institute for Highway Safety

ISA Intelligent Speed Adaptation

ISD Insufficient data
viii

km/h Kilometers per hour

LTCCS Large Truck Crash Causation Study

LTL Less-than-truckload

mi/h Miles per hour

NHTSA National Highway Traffic Safety Administration

NTDC National Truck Driving Championships

OBSS Onboard safety system

OECD Organisation for Economic Co-operation and Development

OEM Original equipment manufacturer

OOIDA Owner-Operator Independent Drivers Association

QEW Queen Elizabeth Way

RoSPA Royal Society for the Prevention of Accidents

SEA Safety evaluation areas

SafeStat Safety Status Measurement System

SL Speed limiter

SRA Swedish Road Administration

TL Truckload

TMA Truck Manufacturers Association

TRB Transportation Research Board

UMTRI University of Michigan Transportation Research Institute

USDOT U.S. Department of Transportation

VMT Vehicle miles of travel

VTTI Virginia Tech Transportation Institute
ix

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x 

EXECUTIVE SUMMARY

INTRODUCTION

Speeding (i.e., exceeding the speed limit or driving too fast for conditions) was a contributing 

factor in 8 percent of all reported large truck crashes (National Highway Traffic Safety 

Administration, 2009). Moreover, the Large Truck Crash Causation Study (LTCCS) reported 

that 22.9 percent of all large truck crashes and 10.4 percent of large truck/passenger car crashes 

were coded as “traveling too fast for conditions” (Federal Motor Carrier Safety Administration, 

2006).

One technology used by truck fleets to lower the overall top speed of their trucks is a speed 

limiter (SL). SLs (also described as speed governors) are devices that interact with a truck engine 

to prevent trucks from exceeding a pre-programmed maximum speed. Many truck fleets use SLs 

to increase safety, prolong engine and brake life, and reduce tire wear. 

From a safety perspective, slowing down large trucks may result in lower travel risks for all 

motorists on the road by possibly reducing collisions and mitigating the severity of collisions that 

do occur. Opponents of SLs may argue that safety can be compromised since speed-limited 

vehicles cannot accelerate to avoid traffic conflicts (for instance, in merging situations), and the 

slower speed of these vehicles relative to the surrounding traffic creates speed differentials. This 

argument cites studies in which speed differentials are correlated with increased crash risk.

Key takeaways from this study are:

• This study represents the most comprehensive investigation that has ever been conducted 

on SLs. 

• The various analyses conducted used data from more than 150,000 trucks that were 

involved in more than 28,000 crashes. 

• Results from multiple analyses indicated a profound safety benefit for trucks equipped 

with an active SL.

• The cost of SL technology is negligible and is a standard feature on new trucks (owners 

only need to activate and set the SL).

• The positive findings in this study were consistent with the bulk of the literature on this 

topic indicating significant safety benefits associated with speed reduction which can be 

achieved through the implementation of SLs. Domain research on the potential downside 

of speed deviations among vehicles that could occur due to the interaction of SL 

equipped vehicles and those without SLs seems to be far outweighed by the significant 

safety benefits associated with a reduction in absolute speed afforded by SLs. 
xi

PURPOSE

The purpose of this project was twofold. The purpose of Phase I was to expand on the recent 

Transportation Research Board’s (TRB) Synthesis Report on the Safety Impacts of Speed Limiter 

Device Limitations on Commercial Trucks and Buses. Fundamentally, the Phase I literature 

review supplemented this TRB synthesis in order to obtain a greater understanding of the 

relationship between current SL research and the trucking industry, based on new regulatory 

initiatives and research findings since the TRB study was completed. The purpose of Phase II

was to identify and assess the impacts on a motor carrier implementing SL technology in fleet 

operations. This task was accomplished by analyzing carrier-owned crash data and driver 

responses. The focus of the current study was to identify: 

• Potential safety benefits, and other benefits, afforded by SLs. 

• Best practices applications

Driver, carrier, insurer, and enforcement official views related to SL implementation. This 

document reports the results of all the tasks performed in this project. 

BACKGROUND AND PROBLEM SCOPE

A literature review was performed to develop an in-depth understanding of the current state of 

SL use in the commercial motor vehicle (CMV) industry. This literature review revealed that the 

most indicative results on the effectiveness of speed limiters are from the United Kingdom 

(U.K.). Here, the crash involvement rate for speed-limited heavy trucks fell 26 percent between 

1993 (when mandated) and 2005. U.K. authorities noted that other contributing factors may have 

influenced the decline, but concluded that SLs at least played a significant role. Although SLs 

have been mandated in Europe for more than 10 years, the literature review process did not yield 

any citations of empirical studies specifically assessing the safety effectiveness of SLs on long 

haul trucks (Transport Canada, 2008a). 

Based on crash data from several studies, speeding was one of the primary factors in motor 

vehicle crashes; this risky behavior was also compared to driving with a blood alcohol 

concentration (BAC) of 0.08 (Evans, 1991). Documented disadvantages to speeding included a 

possible increase in transloading (Fuetsch, 2009), a higher probability of being involved in a 

crash (Elvik, 2004; Kloeden, Ponte, and McLean, 2001; NHTSA, 1987) and an increase in the 

severity of the crash (NHTSA, 1987; OECD and ECMT, 2006; Thiffaut, 2009b). Considered 

collectively, the literature on this topic is favorable regarding the positive benefits of SLs in 

reducing crashes.

The information acquired during the literature review task was used to design the current data 

analysis plan for developing an empirical evaluation of the effectiveness of SLs. 
xii

SPEED LIMITER IMPLEMENTATION IN COMMERCIAL TRUCKING

SLs are standard equipment on new trucks and motorcoaches and have been used for some time, 

with the core technology built into the Engine Control Module (ECM). Historical problems 

related to driver tampering have been alleviated by the current electronic systems. Because the 

SL capability is standard, the cost to implement SLs is negligible, although some additional costs 

do accrue for fleets that use external maintenance centers to change SL settings.

Safety was named as the most important benefit of SLs, for both trucks and motorcoaches. 

Providing drivers with an incentive for improving performance or rewarding past performance 

are other benefits offered to carriers through the use of SLs.

In terms of the use of SLs across the industry, there are a variety of opinions. For trucking, the 

Owner-Operator Independent Drivers Association (OOIDA) contends that owner-operators 

typically do not employ SLs. For company-owned trucks, the surveys conducted by OOIDA 

(2007), the American Transportation Research Institute (ATRI) study (McDonald and Brewster, 

2007), and the TRB (2008) indicated that 60 to 63 percent of fleets use SLs, with variations 

across sectors. The investigation for this report (McDonald and Brewster, 2007) yielded much 

higher estimates for fleets, in the range of 75 to 80 percent. Most motorcoaches operate with 

SLs.

With regard to SL settings, the OOIDA (2007) survey found the preponderance of drivers 

operated from 101–110 kilometers per hour (ki/h) [63–68 miles per hour (mi/h)] but this survey 

possibly did not account for vehicles with SLs set above 68 mi/h. The Engine Manufacturers 

Association (EMA) and the Truck Manufacturers Association (TMA) contend that carriers set 

speeds at or below 113 km/h (70 mi/h). The TRB study (2008) found SL settings generally fall 

within the 105–111 km/h (65–69 mi/h) speed range. In the investigation for this study, SL

settings ranged from 62–70 mi/h. Most commercial motorcoach fleets operate with SLs set at 

116 km/h (72 mi/h); however, many motorcoach companies have settings below 113 km/h (70 

mi/h). 

With regard to variations in speed settings depending on driver skill or the use of cruise control, 

the TRB study found that approximately half of the respondents used the practice of varying 

speed settings, but with only minor differences for cruise control use. However, the investigation 

for this study found that none of the fleets interviewed utilized programs to allow qualifying 

drivers to drive at higher speeds. 

Technology trends indicate that vehicles will eventually be “speed limit aware” based on data 

derived from camera and digital map data. However, it is essential that map updating techniques 

and robust video-based image processing algorithms be implemented and proven, to ensure that 

the vehicle is truly following the correct speed limit, including dynamic speed limits.

PEER REVIEW PANEL 

Because the study addressed both the safety and operational cost aspects of implementing SLs, 

stakeholders from both of these areas were included in the Peer Review Panel designed to ensure 

that the research will provide valid, reliable, and useful results. Two forums that included these 
xiii

stakeholders were held in September: the American Trucking Associations Technology and 

Maintenance Council Fall Meeting and the American Trucking Associations Safety Management 

Council Conference. After approval of the list by the Federal Motor Carrier Safety 

Administration (FMCSA), 27 individuals agreed to participate and were available to attend Peer 

Review Panel meeting. 

Discussion topics in the peer review meeting were: 

• The operational definition of “speed limiter-relevant crashes.” 

• Alternative data sources. 

• Measures of exposure. 

• Time period to include in the study. 

• Representatives of the fleets used for the study. 

• Driver characteristics. 

• Other safety factors. 

• Operational costs. 

• Sample size (number of fleets and trucks). 

SPEED LIMITER EFFECTIVENESS ANALYSIS METHODS

A Retrospective Cohort Approach was accepted as the most appropriate research design for the 

current study. Carrier-collected crash and vehicle data were gathered by the research team. Once 

the data were collected, trained research personnel reviewed each crash file to determine if the 

truck crash was an SL-relevant crash. Although the current study was similar to analyses 

assessing the effectiveness of onboard safety systems (OBSS), studies assessing the safety 

benefits of OBSSs target specific crash types that could have been prevented and/or mitigated 

with the systems (see Dang, 2004; Houser et al., 2009; Jermakian, 2010; Murray, Shackelford, 

and Houser 2009a, b). However, a truck with an active SL has many different crash types, and 

trucks equipped with an active SL will generally not have a crash when the truck is traveling 

above the preset speed (as the truck is prohibited from traveling above the preset speed unless the 

truck is traveling down a grade). Thus, the aim of the current study was to identify the types of 

crashes where an active SL would be most effective in mitigating and/or preventing high-speed 

[posted speed limit 97 km/h (60 mi/h) or greater] truck crashes on highways. No trucks in the SL 

cohort had a speed limiter setting of less than 97 km/h (60 mi/h). 

Trained research personnel that were blind to the SL status of each carrier reviewed several data 

elements included in the crash file to determine if the crash was SL-relevant. Assessing whether 

a crash was SL-relevant was based on four types of information found in the dataset: 

• Location of the crash [e.g., highway with speed limit > 97 km/h (60 mi/h)]. 

• Crash type (e.g., rear-end truck striking). 
xiv

• Contributing factor(s) in the crash (used to exclude crashes; e.g., weather-related). 

• Crash narrative.

SPEED LIMITER EFFECTIVENESS RESULTS

The study collected data from 22 carriers (7 in the non-SL cohort; 15 in the SL cohort) in 

calendar years 2007, 2008, and 2009. Data from two carriers were not of sufficient quality to 

include in the analyses (i.e., it was not possible to determine the location of the crash from two 

carriers). Also, some carriers did not provide crash records for all 3 years; thus, the dataset was 

unbalanced. Because of the lack of mileage information and the unbalanced years collected by 

some fleets, number of trucks per year (truck-year) was used as an exposure measure. Table 1

shows the truck-years involved in one or more crashes as well as the number of crash-free trucks 

over the data collection period. All trucks in the study were Class 7 or 8 trucks. 

Table 1. Number of Crashes and Crash-Free Trucks by SL Status

Crash Status SL Cohort Non-SL Cohort Total

Truck-Years With Single Crash 13,091 2,076 15,167

Truck-Years With Multiple Crashes 520 2 522

Trucks-Year Without a Crash 111,781 10,605 122,386

Total Truck-Years 125,392 12,683 138,075

SL-RELEVANT CRASH RATE

The frequency of trucks involved in crash, crash-free trucks, and crash rate by cohort is listed in 

table 2. Approximately 15 percent of the crashes were identified as SL-relevant crashes (2,372 

out of 15,866). This percentage falls within the observed range of truck crashes coded with 

speeding as contributing factor. For example, speeding (i.e., exceeding the speed limit or driving 

too fast for conditions) was a contributing factor in 8 percent of all reported large truck crashes 

(National Highway Traffic Safety Administration, 2009). Moreover, the Large Truck Crash 

Causation Study (LTCCS) reported that 22.9 percent of all large truck crashes and 10.4 percent 

of large truck/passenger car crashes were coded as “traveling too fast for conditions” (Federal 

Motor Carrier Safety Administration, 2006). Therefore, the assessed SL-relevant crash 

percentage of 15 percent determined in the current dataset seems reasonable and is in line with 

other nationally representative datasets, such as the General Estimates System (GES) and 

LTCCS. 

As shown in Table 2, the overall crash rate for trucks without an SL was higher compared to 

trucks equipped with an SL (16.4 versus 11.0 crashes per 100 trucks/year). To further evaluate 

the safety effects of an SL, the SL-relevant crash rate was calculated. Similar to the overall crash 

rate, carriers without an SL had a much higher rate than carriers with an SL (5.0 versus 1.4 per 

100 trucks/year).
xv

Table 2. Crash Frequency and Crash Rate by SL Status

Frequency SL Cohort Non-SL Cohort Total

SL-Relevant Crashes 1,736 636 2,372

Total Number of Crashes 13,786 2,080 15,866

Total Number of Truck-Years 125,392 12,683 138,075

SL-Relevant Crash Rate* 1.4 5.0 – 

Overall Crash Rate* 11.0 16.4 – 

*The unit for crash rate is the number of crashes per 100 trucks/year. 

The mean overall crash rate and the SL-relevant crash rate across carriers and years in the SL 

cohort (dark red) and non-SL cohort (light red) are shown in Figure 1. Note the mean crash rate 

is the average of crash rates by fleet and year. The raw crash rate, as presented in Table 2, was 

aggregated across all fleets; thus, this approach places more weight on large fleets. The research 

team considered the average of fleet-year level crash as a more robust estimation. What is 

interesting about Figure 1 is that the overall crash rate and SL-relevant crash rate show a 

different pattern. However, an analysis of variance (ANOVA) found there was no significant 

difference in the overall crash rate when comparing the non-SL cohort (9.1 per 100 trucks/year) 

and the SL cohort (11.2 per 100 trucks/year; F(1,45) = 0.22, p = 0.645). This is an important 

finding that will be highlighted later. Furthermore, an ANOVA found that the SL-relevant crash 

rate was significantly higher in the non-SL cohort (2.9 per 100 trucks/year) compared to the SL 

cohort (1.6 per 100 trucks/year; F(1,45) = 6.5, p = 0.014). Note that ANOVA provides a statistical 

test of whether the means of several groups are all equal, and therefore generalizes the t-test to 

more than two groups. ANOVAs are helpful as multiple two-sample t-tests would result in an 

increased chance of committing a type I error. For this reason, ANOVAs are useful in comparing 

three or more means (Hayes, 1994). In summary, the SL cohort had a statistically significant 

lower SL-relevant crash rate than the non-SL cohort, but the overall crash rate between the SL

cohort and the non-SL cohort did not differ statistically. 
xvi 

Figure 1. Chart. Average Overall Crash Rate and SL-Relevant Crash Rate in the SL and Non-SL 

Cohorts. Overall Crash Rate is Not Statistically Significant, and the SL-Relevant Crash Rate is 

Statistically Significant.

These important sets of ANOVA results were followed up with an additional analysis that would 

serve to either confirm or contrast these findings. To further quantitatively evaluate the safety 

effects of SLs, the research team used a negative binomial regression model to model the crash 

count, which is the state-of-practice in modeling accident frequency (Lord and Mannering, 

2010). It is particularly suitable for overdispersion data where the Poisson regression model, 

another commonly used approach, cannot fit the data well. The model in Figure 2 is comprised 

of the following: let Y subscript i subscript j be the number of crashes for carrier i in the year j. 

Note that Y subscript i subscript j is assumed to follow a negative binomial distribution, where

mu subscript i subscript j is the expected number of crashes for carrier i in year j and k is an 

overdispersion parameter.

Figure 2. Equation. Negative Binomial Regression Model.

The mean mu is assumed to be affected by the number of trucks in the carrier and the presence of 

an active SL. The model in Figure 3 is comprised of the following: 

Figure 3. Equation. Log(μij) in the Negative Binomial Regression Model. 
xvii 

where E subscript i subscript j is the number of trucks in carrier i in year j and X subscript i 

subscript j is the vector of covariate and beta is the regression coefficient, alpha subscript i is a 

random effect associated with carrier i. This model incorporated the effects of some carriers 

contributing multiple calendar years of data. The impacts of an active SL can be evaluated by the 

significance of beta. The exponential of beta is the ratio of crash rate between Non-SL cohort 

and SL cohort. 

The model outputs are shown in Table 3 and Table 4. Table 3 provides the estimates for variance 

in the carrier-specific random effect and overdispersion parameter, and Table 4 provides the 

estimates for the effects of an active SL. The overdispersion parameter is much smaller than 1, 

which indicates the presence of overdispersion and is in support of the negative binomial model. 

Consistent with the simple ANOVA above, the presence of an SL showed a significant 

association with the SL-relevant crash rate (p = 0.0295). The estimated SL-relevant crash rate 

ratio was 1.94 (95 percent Confidence Interval: 1.07 to 3.49), which indicates that the SLrelevant crash rate for carriers in the non-SL cohort was twice that for the carriers in the SL 

cohort. Put another way, the rate for SL-relevant crashes was approximately 50 percent of the 

rate for trucks with an SL as compared to trucks without an SL. 

Table 3. The Mixed Effect Model Covariance Parameters Estimates

Covariance Parameter Subject Estimate Standard Error

Intercept Carrier 0.2288 0.1060

Overdispersion Parameter – 0.09642 0.03742

Table 4. The Effects of SL Status on the SL-Relevant Crash Rate

Label Estimate Standard 

Error

P Value SL-Relevant 

Crash Rate 

Ratio

95% 

Confidence 

Interval

Non-SL Cohort vs. SL Cohort 0.6610 0.2875 0.0295 1.94 1.07–3.49

CONCLUSIONS

The primary safety analysis conducted in this study focused on the potential reduction in truck 

crashes that could have been avoided and/or mitigated with an active SL installed. This was the 

first study to use actual truck crash data collected directly from truck fleets, representing a wide 

array of truck crashes (from minor crashes involving a scrape on a mirror to fatal crashes). 

Specifically, the study included data from 20 trucking fleets, approximately 138,000 trucks, and 

analyzed more than 15,000 crashes. In addition, data were collected over a 3-year period (2007–

09). The approach used in this research went far beyond any previous study in this domain. 

The data used in the study were divided into two groups: trucks with an SL and trucks without an 

SL. The crash data were grouped into two groups as well: crashes that were SL-relevant and 

crashes that were not SL-relevant. Analyses included ANOVAs and data modeling (random 

effect negative binomial distribution). The results across analyses indicated a strong, positive 

safety benefit for SLs. 
xviii

The ANOVA resulted in two key findings. First, there was no statistically significant difference 

in involvement in the overall crash rate as a function of truck type (SL vs. no-SL, p = 0.65). 

However, for SL-relevant crashes, there was a strong statistically significant difference in crash 

rates showing a clear benefit for trucks with a SL (p = 0.01). This is an important combination of 

findings and serves as a control of unmeasured variables that could possibly have contributed to 

the benefits observed for the SL cohort. As noted in the U.K. study (Transport Canada, 2008a), it 

is possible that contributing factors other than the presence of a SL might have influenced 

observed benefits. For example, it could be (and this was not measured or controlled for) that 

fleets with SL trucks also had in place a positive safety culture. If so, one could make the 

argument the positive effects observed may not have been due to the SL technology, but rather 

due to other safety protocols (i.e., safety culture). However, if this was the case, one would 

expect to see safety benefits in the overall crash rate as well in the SL-relevant crash rate. Why 

would safety culture, for example, only apply to certain crash types (i.e., SL-relevant)? That is, if 

a confounding variable such as safety culture had played a role, then the benefits (i.e., crash rate 

reductions) would be expected in all crash types. In addition, though not significant, the overall 

crash rate was in the opposite direction of what would be expected if a confounding variable, 

such as safety culture, had played a role. As such, the combination of these two results (i.e., a 

non-significant overall crash rate, but highly significant SL-relevant crash rate) supports the 

hypothesis that trucks equipped with SLs in the current study were effective in reducing SLrelevant crashes. 

Moreover, a second confirmatory analysis was conducted whereby a random effect negative 

binomial distribution model was developed to model the crash count. Similar to the ANOVA 

results, a clear benefit was observed with this analysis approach and a significant SL-relevant 

crash rate reduction was found for trucks equipped with SLs (compared to non-SL trucks). The 

results from the modeling analysis were profound in that the resulting calculated SL-relevant 

crash rate ratio (1.94) was approximately twice that for non SL-equipped trucks compared to 

trucks with an SL. 
xix

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1 

1. INTRODUCTION 

1.1 BACKGROUND

In 2008, speeding (i.e., exceeding the speed limit or driving too fast for conditions) was a 

contributing factor in 8 percent of all reported large-truck crashes (National Highway Traffic 

Safety Administration [NHTSA], 2009). Moreover, the Large Truck Crash Causation Study 

(LTCCS) reported that 22.9 percent of all large truck crashes and 10.4 percent of large 

truck/passenger car crashes were coded as “traveling too fast for conditions” (Federal Motor 

Carrier Safety Administration [FMCSA], 2006). As reported by Klauer, Sudweeks, Hickman, 

and Neale (2006): 

The dramatic risk of vehicle speed is illustrated by the estimated annual savings 

of 2,000 to 4,000 lives as a result of the nationwide reduction in the highway 

speed limit to 55 miles per hour (mi/h) in 1974 (Waller, 1987). When the national 

speed limit was later raised to 65 mi/h, the occurrence of vehicle crashes showed 

a marked increase (Evans, 1991). A recent analysis by Patterson, Frith, Povey, 

and Keall (2002) of the repeal of the National Maximum Speed Limit in 1996 

supported Evans’s (1991) data. Patterson et al. (2002) found that 23 States had 

raised their rural interstate speed limits to 70 or 75 mi/h and modeled the number 

of vehicular fatalities on rural interstates from 1991 to 1999 against the new 

speed limits in these States (i.e., 75 mi/h, 70 mi/h, or no change). Vehicular 

fatalities in the group of States that had raised their speed limits to 75 mi/h and 

70 mi/h were higher than expected as compared to fatalities in the States that did 

not change their speed limits. 

Similarly, a rigorous meta-analysis conducted by Elvik, Christensen, and 

Amundsen (2004) included 97 different studies with a total of 460 estimates of the 

relationship between changes in speed and changes in the frequency of crashes or 

associated injuries and fatalities. Using the Power Model, this study assessed the 

relationship between speed and road safety. The study concluded there was a 

relationship between speed and the number of crashes and the severity of crashes. 

In fact, the data suggest that speed is likely to be the single most important 

determinant in the frequency of traffic fatalities; a 10 percent change in the mean 

speed of traffic is likely to reduce fatal traffic crashes by 34 percent and have a 

greater impact on traffic fatalities than a 10 percent change in traffic volume. (pg. 

15–16). 

These data suggest that increases in posted speed limits increase crash risk and severity; 

increases in vehicle speed should also be associated with increases in crash risk and severity. 

This seems intuitive as “speeding reduces a driver’s ability to steer safely around curves or 

objects in the roadway, extends the distance necessary to stop a vehicle, and increases the 

distance a vehicle travels while the driver reacts to a dangerous situation” (NHTSA, 2009). The 

impact force during a vehicle crash varies with the square of the vehicle speed, so even small 

increases in speed have large and potentially lethal effects on the force at impact (Roads and 
2 

Traffic Authority, 2005). This is likely to be exacerbated in large trucks given their considerable 

weight (more than 10,000 pounds). 

1.1.1 Speed Limiters

One technology employed by truck fleets to lower the overall top speed of their trucks is a speed 

limiter (SL). SLs (also described as speed governors) are devices that interact with a truck engine 

to prevent a truck from exceeding a preprogrammed maximum speed. Many truck fleets use SLs 

to increase safety as well as to reduce tire wear. A synthesis on the safety impacts of SLs in 

commercial truck and buses found mixed support for the use of these devices in reducing crashes 

(Bishop et al., 2008).

1.2 OVERVIEW OF THE CURRENT REPORT

The purpose of this project was to identify and assess the impacts of implementing SLs in fleet 

operations on motor carriers. These impacts may be related to safety by reducing the number and 

severity of crashes, and/or address operational issues such as tire wear. This report is the second 

report of a two-phase approach. Phase I (summarized below) centered on a detailed literature 

review that updated and expanded on the recent TRB’s Synthesis Report on the Safety Impacts of 

Speed Limiter Device Limitations on Commercial Trucks and Buses (Bishop et al., 2008). Phase 

II involved a series of additional tasks focused on a detailed research design and analysis, a peer 

review process, evaluation of SL implementation, best practices applications, and identification 

of carrier, insurer, and enforcement official views related to SL implementation.

1.3 SPEED LIMITER LITERATURE REVIEW

This section of the report is comprised of annotated literature review findings related to SL 

research and summarizes the information therein. SL applications, safety benefits, crash 

relationships, and research conducted thus far have been the primary focus of this review. 

International rulemaking for SLs in Canada, the United Kingdom (U.K.), the European Union 

(EU), and Australia have also been included to provide a general understanding of how the 

subject has been addressed by various countries (other than the United States). 

Literature sources consisted of industry, academic, and government data and publications, plus 

direct communications with government officials in other countries. See Appendix A for the full 

list of organizations contacted. 

The research gathered has been summarized and grouped into the following sections: 

• Safety impacts of speed. 

• SL regulations. 

• Technologies and usage. 

• Safety results from implementation. 

• Other benefits attributed to SLs. 
3 

Some of the source documents were very comprehensive and addressed several of the different 

categories. In such cases, they are cited multiple times within the overall document as pertinent 

to particular sections. For the purposes of this literature review, SLs were defined as a device that 

connects to the vehicle’s Engine Control Module (ECM) and programmed to manage travel 

speeds at particular settings. There are several definitions for “speeding,” in the current report the 

term “speeding” was defined as vehicles traveling speeds in excess of the posted speed limit, as 

well as driving faster than what is safe for roadway conditions. For instance, environmental 

factors—such as adverse weather conditions—may necessitate that driver’s travel at rates below 

the posted speeds. 

1.3.1 Safety Impacts of Speed

This section of the literature review examines the literature relating vehicle speed to safety. 

1.3.1.1 Speed Limit Compliance Trends

Studies of combined passenger car and truck traffic have shown that exceeding the speed limit is 

widespread on U.S. interstate highways (Insurance Institute for Highway Safety [IIHS], 2003). 

However, one study measuring truck speeds in eight different locations found that the majority 

of trucks were traveling within the posted speed limits (IIHS, 2008). 

The U.K. Department for Transport (2007) reports that only a small number of heavy trucks 

exceeded the motorway posted speed limit of 97 kilometers per hour (km/h) or 60 mi/h. When 

the speed limit was 80 km/h (50 mi/h) on dual carriageway rural roads, and 40 mi/h on single 

carriageway rural roads, trucks exceeding the speed limit were 82 percent and nearly 75 percent, 

respectively. 

Insurance Institute for Highway Safety (2008). Hit a fastball and you might score a run. Hit 

something in a speeding car and you might land in the hospital or worse. Special Issue: Speed. 

Insurance Institute for Highway Safety, 43. 

A total of eight urban, suburban, and rural interstates were studied to determine the typical travel 

speed, including: Albuquerque, Atlanta, Boston, Denver, Los Angeles, Omaha, Tampa, and 

Washington, DC. The study was based on a limited period of observations and was not intended 

to definitively or comprehensively assess truck speeds. In urban areas, the vehicles were 

traveling in excess of posted speeds for all metropolitan locations. However, suburban and rural 

interstates displayed higher average speeds in only half of the locations. 

Table 5 shows the proportion of trucks that were speeding and within the speed limit by location.

As can be seen, the majority of trucks were traveling within the posted speed limit. Researchers 

concluded that, on average, trucks tended to remain at lower speeds than passenger vehicles.
4 

Table 5. Percent of Trucks Speeding by Location

Location Posted Speed 

Limit

Trucks 

Speeding

Trucks Within 

Speed Limit

Total 

Urban

Tampa 55 0% 100% 100%

Denver 55 0% 100% 100%

Omaha 60 21% 79% 100%

Suburban and Rural

Los Angeles 75 1% 99% 100%

Tampa 70 29% 61% 100%

Intercity Segments

Atlanta 70 5% 95% 100%

Los Angeles 55 15% 85% 100%

Washington, D.C. 65 18% 82% 100%

Insurance Institute for Highway Safety (2003). Faster travel and the price we pay. Special 

Issue: Speeding. Insurance Institute for Highway Safety, 38. 

This article noted studies by the Land Transport Safety Authority of New Zealand, which 

examined the number of deaths associated with increased speed limits in the United States during 

1995 and 1996. States that raised posted speed limits to 121 km/h [75 mi/h (from 105 km/h or 65 

mi/h)] had 38 percent more deaths (per million miles) than States that did not increase posted 

speed limits. Similarly, States that raised limits to 113 km/h (70 mi/h) had a 35 percent increase 

in deaths. 

When IIHS studied vehicle travel speeds in six States, findings corresponded with those of 

previous studies. Out of the six States, almost all had vehicles traveling in excess of 113 km/h 

(70 mi/h) or faster 67 percent of the time. However, Colorado had 25 percent of vehicles 

traveling more than 129 km/h (80 mi/h). 

The report suggested that increased speeds can be attributed to a variety of factors. One

explanation may be that car manufacturers are advertising faster, more powerful vehicles to 

appeal to the public. In addition, there do not seem to be any negative stigmas attached to 

speeding since it is assumed to be the accepted norm.

U.K. Department for Transport (2008). Transport Statistics Bulletin: Road Statistics 2007: 

Traffic Speeds and Congestion. Transport Statistics Bulletin, 08, 20. 

This compilation of national data reported variability in vehicles exceeding posted speed limits, 

depending on the situation. Specifically for heavy trucks, the data showed that only a very small 

number of vehicles exceeded the motorway speed limit of 97 km/h (60 mi/h). When the speed 

limit was 80 km/h (50 mi/h) on dual carriageway rural roads, and 64 km/h (40 mi/h) on single 

carriageway rural roads, trucks exceeding the speed limit were 82 percent and nearly 75 percent, 

respectively. 
5 

1.3.1.2 Speed as a Causal Factor in Crashes 

Elvik, R. (2004, November). Speed, speed cameras and road safety evaluation research. Paper 

presented at the meeting of the Royal Statistical Society. 

A meta-analysis was conducted to determine the overall effect of speed reductions on the number 

and severity of injuries to road users. This before-and-after analysis employed the Power Model

equation to compute results (Figure 4). Therefore, using the following proposed equation, a 

reduction of speed from 115 km/h (72 mi/h) to 105 km/h (65 mi/h) would reduce fatal accidents 

by an estimated 30.5 percent. 

Figure 4. Equation. Power Model

For the meta-analysis, researchers identified a total of 174 speed-related studies. Of those, 97 

contained enough information to be included in the assessment, which consisted of 460 estimates 

of the benefits associated with reduced speed. When the meta-analysis results were concluded, 

researchers noticed a slight deviation from the proposed equation. However, the findings came 

within reasonable expectations of the originally recommended exponent values, and the model 

was revised so that the incident types were counted as mutually exclusive events. Table 6

displays the revised exponent values. 

Table 6. Assessment of Injury Severity Relative to Speed

Incident Type Revised 

Exponent

95% Confidence 

Interval

Injury Severity.

Fatalities 4.5 4.1–4.9

Seriously Injured Road User 2.4 1.6–3.2

Slightly Injured Road User 1.5 1.0–2.0

All Injured Road Users (Including Fatalities) 1.9 1.0–2.8

Accident Severity.

Fatal Accidents 3.6 2.4–4.8

Serious Injury Accidents 2.0 0.7–3.3

Slight Injury Accidents 1.1 0.0–2.4

All Injury Accidents (Including Fatal) 1.5 0.8–2.2

Property-Damage-Only Accidents 1.0 0.0–2.0

The study concluded that the strong linear relationship between speed and road safety may be 

causal. This indicates that if vehicle speed is reduced, there will also be a decrease in the number 

of crashes and injuries. Although researchers pointed out several limitations to the study 

(publication bias, extraneous variables, data reliability, etc.), there was a general consensus that 

the limitation factors most likely did not have an effect on the results. Perhaps the most 

important implication noted was that speed reduction was the most critical factor related to 

improving traffic safety.
6 

Patterson, T.L., Frith, W.J., Povey, L.J., and Keall, M.D. (2002). The effect of increasing 

rural interstate speed limits in the United States. Traffic Injury Prevention, 3, 316-320. 

After the repeal of the National speed limit laws, many States changed their maximum speed 

limits on interstates. Within a year of the change, 23 States had implemented speeds of 113 km/h 

(70 mi/h) and 121 km/h (75 mi/h): 24–32 km/h (15–20 mi/h) above the once-required National 

speed limit of 55 mi/h. In order to fully understand the effect this change had on crash and 

fatality rates, the authors compared crash data between 1992 and 1999. The crash trends were 

analyzed both before the repeal (1992–95) and after (1996–99). It was determined the increased 

posted speed limits had a strong link to the fatality rate. For those States that increased the 

maximum speed to 121 km/h (75 mi/h), fatalities increased 38 percent. In States where the new 

limit was 113 km/h (70 mi/h), fatalities increased 70 percent. According to the authors, this 

connection further solidifies the argument that drivers traveling at faster speeds are more likely 

to be in a fatal accident.

Kloeden, C.N., Ponte, G., and McLean, A.J. (2001). Traveling Speed and the Risk of Crash 

Involvement on Rural Roads. Department of Transport and Regional Services, Australian 

Transport Safety Bureau, Road Accident Research Unit, Adelaide University. 

In this study the relationship between vehicle speed and the likelihood of fatal crash involvement 

was assessed. Stipulations for study inclusion consisted of crashes that occurred in rural 

locations, had vehicles traveling in excess of 129 km/h (80 km/h), or resulted in at least one 

fatality or hospital treatment. Research team members were notified of an accident by the South 

Australian Ambulance Service and a total of 167 cases met the preliminary criteria for study 

inclusion. However, after assessing all information, the final sample consisted of 83 vehicles. 

Crash reconstruction was used to determine the speeds traveled prior to the crash. Thus, speed 

and crash data were analyzed using a modified logistic regression formula, which examined the 

risk that a passenger vehicle might become involved in a fatal crash based on the speed traveled 

above the average travel speed. Findings implied that when traveling more than 10 km/h (6 mi/h) 

above the average speed, the likelihood of having a fatal crash was two-fold higher than noncrash vehicles. Interestingly, evidence indicated that vehicles traveling at slower than average 

speeds were less likely to have a fatal crash. 

National Highway Traffic Safety Administration. (1987). Heavy Truck Safety Study. Report 

No. DOT-HS-807-109. National Highway Traffic Safety Administration, Washington, DC. 

In response to a Congressional Directive, NHTSA conducted an in-depth analysis of large-truck 

crashes. In addition to identifying the interrelated factors that contribute to large-truck crashes, 

the report provided enforcement agencies with a discussion of programs that facilitate 

commercial motor vehicle (CMV) traffic law compliance. The report listed near-term actions 

that could improve heavy-truck safety as well as proposed research initiatives for long-term 

solutions. 

NHTSA found that there were many interrelated factors that contribute to these crashes. The 

report identified vehicle-related factors, including braking and handling/stability, and driverrelated factors (including speeding). The report found that higher speeds have a direct impact on 
7 

the severity of a crash outcome. The study also found a much higher percentage of drivers 

involved in crashes who were exceeding a reasonable safe speed (12.8 percent) than were 

exceeding the posted speed limit (0.9 percent). This suggests that SLs may not address one of the 

top factors in large-truck crashes: traveling too fast for conditions. 

Office of Motor Carrier Safety. (1999). Analysis Brief: Speeding-Related Multi-Vehicle Fatal 

Crashes Involving Large Trucks. Publication No. MCRT-00-004. Office of Motor Carrier 

Research and Standards, Washington, DC. 

This study of fatal large-truck crashes found that up to 21 percent of large-truck crashes (n = 

982) included the attribute of speeding. The study compared crashes that involved speeding to 

those that did not. As seen in Table 7, speeding vehicles had a higher percentage of crashes than 

those traveling at the posted speed limit for rural interstates, urban interstates, and urban 

freeways. On the contrary, crashes in which the vehicles were traveling at the posted speed limits 

were more likely to occur than those speeding in “rural other” and “urban other” areas.

Table 7. Distribution of Crashes by Roadway Locations

Roadway Location Speed-Related Crashes Crashes Within Posted Limit

Rural Interstate 18% 10%

Rural Other 47% 59%

Urban Interstate 13% 8%

Urban Freeway 5% 3%

Urban Other 17% 20%

Total 100% 100%

Federal Motor Carrier Safety Administration (2007b). Large Truck Crash Causation Study. 

LTCCS Summary. Report No. FMCSA-RRA-07-017. Federal Motor Carrier Safety 

Administration, Washington, DC. 

This study examined the factors that increased the likelihood that a large truck would become 

involved in a crash. Sampling consisted of data from 963 crashes that were collected across 24 

site locations in 17 States. Researchers were responsible for collecting data immediately after a 

crash, which consisted of interviewing persons involved, inspecting vehicles at the scene, and 

any documentation that might have been available at the time. 

Speeding was included among the primary factors in motor vehicle crashes. Specifically, 

traveling too fast for conditions was the second highest factor at 23 percent; almost all of these 

speeding events occurred below posted speed limits. The report notes that the data presented may 

not be entirely representative of the population as the results were estimated from the sample 

data.

American Transportation Research Institute. (2009). Speed Limiter Research. American 

Transportation Research Institute, Arlington, VA.

In this study researchers collected passenger and large-truck speed data through the use of a 

radar gun. A total of 515 measurements were taken, accounting for 276 large trucks and 239 
8 

passenger vehicles. Findings indicated that speed differentials between passenger and large-truck 

vehicles were prevalent even when the posted limits were the same for both groups. 

The researchers also found that, in a 121 km/h (75 mi/h) zone, trucks were compliant with the 

posted speed 92 percent of the time, whereas passenger vehicles were only compliant 45 percent 

of the time. This indicates that trucks may have a much lower speed ceiling than their passenger 

counterparts. Using LTCCS data, researchers examined truck-related crashes and incidents 

involving speeding (see Table 8). The following table shows that traveling too fast for conditions 

(i.e., speeding) occurred in 27.8 percent of the large-truck crashes. However, only 2.8 percent of 

all crashes were related to speeding in excess of the posted speed limit (exceed limit values 

added). This suggests that, even though nearly one-third of large-truck crashes involved traveling 

too fast for conditions, only 2.8 percent of the total crashes would be influenced by limiting 

vehicles to the posted speeds. 

Table 8. Data Regarding Speeding, Speed Limits, and Crashes

Condition Percentage

Speeding Total 27.8%

Exceed Limit (>5mi/h) 2.3%

Exceed Limit (≤5 mi/h) 0.4%

Not Exceed Limit 8.0%

Unknown 17.0%

No Speeding 72.2%

Exceed Limit (>5mi/h) 0.8%

Exceed Limit (≤5 mi/h) 1.8%

Not Exceed Limit 36.9%

Unknown 32.7%

Total 100.0%

National Highway Traffic Safety Administration. (2007a). Large Truck Crash Facts. National 

Highway Traffic Safety Administration, Washington, DC. Available at http://wwwnrd.nhtsa.dot.gov/Pubs/811017.PDF. 

In 2007, for the first time in more than 10 years, the total number of fatalities for all vehicle 

types declined to a level that has not been seen since 1994. Since 2006, there has been a 

reduction in fatalities by 3.9 percent—a record low since 1992. Passenger-vehicle fatalities have 

been decreasing over the past 5 years, whereas light trucks fatalities have had the same rate for 2 

consecutive years. Interestingly, the fatality rate of all vehicles per 100 million vehicle miles of 

travel (VMT) has continued to decline despite the fact that VMT has also decreased (from 2006 

to 2007). 

Evans, L. (1991). Traffic Safety and the Driver. Van Nostrand Reinhold, New York, NY.

This research effort conducted an in-depth analysis of traffic safety data and the factors 

underlying the crashes. The author recounted the dramatic decline in drunk driving and attributed 

at least some of this decline to the fact that drunk driving has become socially unacceptable. 
9 

However, the author noted a lack of social pressure to reduce other harmful driving practices, 

such as speeding.

The author correlated drivers traveling 105 km/h (65 mi/h) in an 89 km/h (55 mi/h) zone to an 

increase in the risk of involvement in a fatal crash. This risky behavior was cited as being similar 

to that of a driver with a blood alcohol concentration (BAC) of 0.08 percent. Evans suggested 

that post-crash alcohol testing provides key evidence of impaired driving, but measurements of 

speed and the role speeding plays in crashes are less reliable. This results in a lack of data 

documenting speeding as a causal factor; thus, the role of speeding as a factor in crashes was 

significantly underestimated. Lastly, Evans noted that speed is a central component in helping to 

reduce the risk of a crash.

Hickman, J.S., Knipling, R.R., Olson, R.L., Fumero, M.C., Blanco, M., and Hanowski, R.L.

(2005). Phase I: Preliminary Analysis of Data Collected in the Drowsy Driver Warning System 

Field Operational Test. Contract No. DTNH22-00-C-07007, Task Order No. 21. Federal Motor 

Carrier Safety Administration, Washington, DC. 

NHTSA and FMCSA funded a field operational test (FOT) of a drowsy driver warning system. 

The study included 103 drivers and 43 trucks. The FOT collected data, via onboard safety 

systems and multiple cameras, and evaluated the effectiveness and limitations of a driver 

drowsiness monitoring system. The study found that minimizing driver internal distractions and 

increasing defensive driving techniques were essential. The study reported that the top 

contributing factors in crashes were inattentive/distracted drivers (35.7 percent), apparent 

unfamiliarity with the roadway (28.6 percent), and drowsy/asleep (21.4 percent). These findings 

suggest that, although SLs will likely not mitigate two of the top three contributing factors 

(inattentive/distracted drivers and drowsy/asleep drivers); SLs could play a role in reducing 

crashes that occur when a driver is unfamiliar with a roadway. This would apply to situations in 

which the driver is exceeding the posted speed limit, but not in cases where the driver is driving 

too fast for conditions. SLs may also reduce the frequency of crashes involving inadequate 

evasive action (14.1 percent). However, the efficacy of SLs in reducing these incidents is 

predicated upon whether or not the driver is exceeding the posted speed limits or traveling too 

fast for conditions. 

Organisation for Economic Co-Operation and Development and European Conference of 

Ministries of Transport (2006). Transportation Research Centre: Speed Management. ISBN 

92-821-0377-3. Organisation for Economic Co-Operation and Development (OECD) and 

European Conference of Ministries of Transport (ECMT). 

This report provided perspectives and recommendations regarding speeding and speed 

management based on the joint efforts of representatives from several OECD countries. 

Although traveling at greater speeds may provide some benefits for decreasing the amount of 

time to deliver goods, the time saved may not be that substantial for shorter distances and can 

pose safety threats. Reaction times, information processing, and actions taken to respond to 

driving situations while speeding are factors that can have detrimental effects on crash likelihood 

as the time to react and stop a vehicle increases dramatically as speed rises. When speeding and 

poor roadway conditions (such as wet pavement) are combined, stopping distance is delayed by 

an additional 25 percent. 
10 

There have been many factors identified that contribute to the probability of being involved in a 

crash. One finding suggests that the difference in speed between cars and trucks can have a 

significant negative impact on crash rates. As the differences in speed increase between vehicles, 

an adverse event becomes increasingly plausible, based on crash exposure. Also, crashes that do 

occur tend to be more severe when speeding has been involved. Furthermore, crash severity has 

been shown to be dependent on the mass difference of vehicles involved—where large truck 

mass can be up to 20 times greater than cars, signaling a safety concern.

The report addressed the impact of speed variance on crashes. The authors note that speed 

variance is particularly important in urban areas, given the mix of different types of motorized 

users with non-motorized users. The issue also arises for highways on steep hills (both up and 

down hills), where the speed differential between passenger cars and trucks can be large. The 

report notes that when differences in speed were large, passing maneuvers increase, thereby, 

increasing crash risk. Further, such speed dispersion is strongly related to road fatalities on 

interstate highways, rural roads, and arterials. 

This report’s discussion of speed dispersion highlights the many dimensions of this issue. 

Research on speed dispersion must be carefully examined to determine if it applies to the 

relatively small speed differences that occur between speed-limited trucks and those exceeding 

the posted speed limit. 

The authors believed speed management should be part of any national road safety strategy, as a 

means of achieving policy goals for safety as well as mobility and environmental benefits. They 

assert this should be coupled with analyses to set appropriate speed limits for all types of roads, 

based on crash risk and other factors such as presence of vulnerable road users and roadside 

characteristics. Their recommendations are bolstered by the successes achieved in three countries 

due to changes in posted speed limits and enforcement strategies. Starting in 2002, France 

adopted an enforcement strategy which included both a strong focus on speed enforcement and 

the introduction of automatic enforcement. Over the course of 3 years, the average speed on 

French roads decreased by 5 km/h (3 mi/h) and fatalities decreased by more than 30 percent. 

Also in 2002, the Australian state of Victoria launched their Arrive Alive! Strategy, which 

included an initiative to reduce vehicle speeds via increased enforcement. Decreases in the 

average speed were observed, especially in 60, 70 and 80 km/h zones (37, 44, and 50 mi/h), 

resulting in a 16 percent reduction in fatalities in 2005 as compared to 2002. A 43 percent

reduction in fatalities also occurred in metropolitan Melbourne from 2001 to 2003. The authors 

note that it is difficult to attribute these reductions solely to speed factors; however, the role of 

reduced speed is at least suggestive. In Hungary, the speed limit within urban areas was reduced 

from 60 km/h to 50 km/h in 1993, and resulted in a reduction of 18.2 percent in crash fatalities in 

the following year.

Thiffault, P. (2009b). SPEED: Section 1: Speed and safety (first draft). Currently unpublished. 

Transport Canada, Ottawa, Canada. 

Based on a broad literature review, the author concluded that the relationship between speed and 

safety hinges on four key points: speed diminishes the ability to drive safely, speed is a major 

contributor in crashes, speed factors interact with crash rates in a variety of ways, and speed has 

a severe impact on crash severity.
11 

It was concluded that speed contributes to crashes; however the evidence is multifaceted and 

complex. The report cites a range of studies to conclude that speed and speed dispersion are 

associated with crash involvement in the following ways: crash risk is lower near the average 

speed and higher for vehicles traveling much faster and much slower, and crash probability and 

severity increases with speeds that are higher than the surrounding traffic flow. 

The author concluded that absolute speed is more important than speed variance. First, there are 

common crash types in which the consequences are not related to speed variance, such as singlevehicle and head-on crashes. Secondly, absolute speed affects the time available for a driver to 

handle an impending crash situation, as well as the energy in a crash which does occur. The 

author refers to literature which notes that when speed variance is decreased by having the 

slower drivers drive faster, there is an increase in mean speed and an increase in crashes; only 

when reduction of speed variance is brought about by reductions in mean speed does crash rate 

decrease. 

1.3.2 Speed Limiter Regulations

This section examines policy and regulatory issues relating to SLs in different countries. 

1.3.2.1 Australia

Australian National Transport Commission (2008). Sharing Responsibility for Heavy Vehicle 

Speed Compliance. Available at http://www.ntc.gov.au/NewsDetail.aspx?newsid=252. 

The article notes that “Chain of Responsibility” laws that target the cause of heavy-vehicle 

speeding have been approved unanimously by the Australian National Transport Council 

(ANTC). According to the ANTC, the focus of the new laws is on the underlying cause of 

heavy-vehicle speeding—shippers and other off-road parties in the logistics chain whose 

delivery schedules and deadlines put pressure on drivers to break road laws. Overall, the 

intention is to create a culture where speeding is not tolerated. 

Chain of Responsibility reforms agreed on by Transport Ministers now cover heavy-vehicle 

overloading, driver fatigue, and speed offenses. The article notes that all state governments have 

agreed to implement the model Chain of Responsibility laws for speed compliance within 12 

months. Out-of-compliance penalties include court-imposed corporate fines of up to $50,000 

plus three times the estimated commercial benefit gained by breaking the law. 

Ballingall, S. (2007). Speed Limiters on Heavy Vehicles in Victoria, Australia. Email 

Correspondence. VicRoads Vehicle Safety Department. 

SLs are defined in Australian Design Rule 65 as devices which limit the maximum speed of a 

vehicle. The rule requires all heavy trucks greater than 12 tons gross vehicle mass (GVM) and all 

buses greater than 5 tons GVM to be fitted with an SL (to be set to limit the maximum speed by 

deceleration to no more than 100 km/h or 62 mi/h). The author notes that speed-limited vehicles 

can travel faster than the speed to which the limiter is set—in excess of 15 km/h (9 mi/h) above 

the speed-limited speed if going downhill when at or near maximum legal vehicle mass. The 

author notes that SL tampering is a major concern. At the time of this writing, ways to make SLs 

more tamper proof and/or tamper evident were being examined. 
12 

Australian National Transport Commission (2006). Heavy Vehicle Speed Compliance: Draft 

Proposal and Draft Regulatory Impact Statement. Australian National Transport Commission, 

Melbourne, Australia. 

The Australian Design Rule 65, introduced in July 1990, mandated that large trucks and buses be 

fitted with an SL set to a maximum speed of no more than 100 km/h. To further improve safety, 

the ANTC adopted the National Vehicle Safety Strategy 2003–10 in an effort to reduce injuries 

and fatalities caused by large-truck crashes. One of the objectives of the Strategy is better speed 

management and recognition that heavy-vehicle speed compliance is only one of the factors in

safety-based outcomes. In 2005, the ANTC conducted a review of large-truck compliance with 

posted speed limits and evaluated several regulatory proposals. Based on these economic 

analyses, the ANTC proposed regulatory mechanisms that best improves safety-based outcomes.

The proposed approach, with the most positive benefit-cost ratio, is based on the development of 

a “chain of responsibility for speed compliance.” This approach places at least some 

responsibility on all supply chain stakeholders that may influence whether or not speeding 

occurs. In essence, these stakeholders must ensure that the driver is not required to speed to 

complete a road transport task. The report estimates that 10 to 30 percent of SLs have been 

tampered with, and that 100 percent compliance by large trucks with SLs would result in 29 

percent fewer large-truck crashes. 

1.3.2.2 Canada 

Transport Canada sponsored a series of studies in 2007–08 that can be considered the most 

significant body of work recently published on the topic of SLs. The Transport Canada (2008d) 

Summary Report is their summary of the results of this multidimensional set of studies. The 

studies addressed safety implications, international factors, technical considerations, trade and 

competitiveness impacts, and environmental benefits. Also, a case study was performed

involving key motor carriers. The detailed safety-relevant results of these studies are covered 

below in the section titled “Safety Results from Implementation.” In January 2009, SLs became 

mandatory in CMVs in the Canadian provinces of Ontario and Quebec. The laws require that 

trucks be governed at a maximum speed of 105 km/h. 

Transport Canada (2008d). Summary Report: Assessment of a Heavy Truck Speed Limiter 

Requirement in Canada. Transport Canada No. TP-14808. Transport Canada: Ottawa, Canada. 

This report is Transport Canada’s summary of the results of a multidimensional set of studies 

conducted during 2007–08. The focus of these studies is summarized here, with pertinent results 

summarized in later sections. A Safety Implications Study was conducted to determine whether 

SLs would reduce the risk and severity of crashes for trucks. The study assessed the safety 

impact of speed differentials and car-truck interactions in a speed-limited environment. Traffic 

simulations for three highway scenarios were conducted for the study as well as a case study of a 

freeway section in the Toronto area. An international assessment examined the experiences in

three countries (Australia, Sweden, and the United Kingdom) with SL legislation in place. 

The International Assessment noted the importance of a consistent national approach to SL

compliance, based on comments from stakeholders interviewed. There exists a tension between 

consistency and legislative flexibility at the state level (across Australia) and the national level 
13 

(across Europe). The European requirement provides this consistency across European Union 

(EU) Member States (i.e., that the SL must be set at 90 km/h for all trucks greater than 12 tons). 

In the case of Australia and Sweden, regulations and policies proposed at the national level are 

not always adopted at the state, territorial, or county level and this has led to inconsistencies in 

regulatory approaches toward enforcement and compliance. 

A case study involving two large Canadian carriers was conducted to document the benefits and 

experience of SL usage within the Canadian trucking industry. Both firms, representing the forhire and private trucking sectors, have operated with SLs since the mid 1990s. They believe SLs 

have had a significant positive impact on safety and maintenance costs. 

A Technical Considerations Assessment summarized technical issues and limitations of 

electronic SLs with respect to compliance, enforcement, and tampering. The summary was based 

on survey responses from truck and engine manufacturers. Other studies examined trade and 

competitiveness impacts and environmental benefits. 

Fuetsch, M. (2009). Soft enforcement of limiters underway for all truck drivers in Ontario, 

Quebec. Transport Topics, 3828, 2. 

SL laws for CMVs took effect in January 2009 in the Canadian provinces of Ontario and 

Quebec. The laws require that trucks must be governed for a maximum speed of 105 km/h

(slightly over 65 mi/h). In the first six months, law enforcement agencies conducted “soft 

enforcement,” with an emphasis on stopping drivers and reading SL settings, rather than issuing 

citations for non-governed or inadequately governed trucks. Enforcement will check SL settings 

primarily at weigh stations and public officials estimate 2 to 5 minutes will be added to 

inspection times. The law requires that trucks hauling freight bound for either province must use 

limiters with the properly set maximum speed or relinquish freight at the border. A segment of 

the industry believes the law will increase “transloading” of freight at the provincial borders 

from non-governed trucks to those with governors. 

Supporters of the SL law cite two primary benefits: safety improvements and better fuel 

economy (thereby reducing greenhouse gas [GHG] emissions). However, the industry remains 

divided over the law. The Owner-Operated Independent Drivers Association (OOIDA) continues 

to oppose the law, citing concerns over its benefits, the training for law enforcement, and the 

need for equipment to access limiter settings via the engine control module. Conversely, another 

segment of the industry sees little or no impact to operations due to existing SL settings already 

at or below the mandated maximum speed. These carriers note that adoption of these lower 

settings improve safety and increase fuel economy. 

American Trucking Associations. (2008). Ontario Ministry of Transportation Carrier and 

Enforcement Branch Proposed Regulations on Speed Limiters. American Trucking Associations, 

Arlington, VA. 

The American Trucking Associations (ATA) recently advocated for the use of SLs within the 

United States to increase highway safety for users. The specific petition suggested that NHTSA 

and FMCSA proceed with rulemaking for the use of SLs in the United States. In the request, 
14 

vehicle manufacturers would be required to set speeds at no more than 109 km/h (68 mi/h) on 

newer trucks and any adjustments to the devices would be prohibited. 

Although Ontario’s vision is generally supported, there were a few recommendations to consider 

prior to implementing the rulemaking:

• Newer CMVs would fall under the SL requirement since older vehicles might lack the 

technology to install the systems properly. 

• Original Equipment Manufacturers (OEM) would have the final say in what qualifies as a 

speed-limiting system since methods to install the device would differ across 

manufacturers. 

• Elimination of the requirement that a device is only functioning properly if the system 

prevents the vehicle from traveling more than 105 km/h (65 mi/h) on level ground. 

• A threshold of 10 percent would be allowed to compensate for environmental factors that 

may temporarily cause a vehicle to travel faster than the set limit. 

• All CMVs should be included in the proposed action, with the exception of emergency 

vehicles. 

• Vehicle control modules would reflect the accurate settings at the time of manufacture to 

prevent minor speed variations that may occur with maintenance, tire size, and other 

factors.

Gillam, T. (2006). Ontario, Quebec plans advance to impose truck speed limiters. Transport 

Topics, 3696, 30-31. 

Prior to the adoption of SL laws in Ontario and Quebec, the industry remained divided over the 

use and efficacy of limiters to achieve the purported benefits of improving safety. Proponents of 

the bill cite improved CMV safety by reducing both the number and severity of large-truck 

crashes. Opponents of mandated SLs opined that reducing the speed of CMVs, and not 

automobiles, would adversely impact safety as the interaction between CMVs and automobiles 

increases. In addition, the industry remains concerned over how enforcement and regulation will 

be conducted as well as the proliferation of disparate provincial-level regulations.

Canadian Trucking Alliance (2006). News Release: Canadian Trucking Alliance Wants to Put 

the Brakes on Speeding Trucks. For Release on March 2, 2006. 

As an active representative of more than 4,500 trucking companies, the Canadian Trucking 

Alliance focuses on increasing safety among roadway users. In 2006, the organization endorsed a 

national policy that would require SLs on all trucks. Maximum speeds would be set to 105 km/h

(65 mi/h). The laws would affect Canadian trucks and those entering the country as well. The 

primary benefits associated with the devices would include: fuel savings, reduced GHG

emissions, fewer severe crashes, improved lane discipline, and a decrease in tailgating.
15 

1.3.2.3 Europe 

Royal Society for the Prevention of Accidents. (2001). Response to the DTLR’s Invitation to 

Comment on the European Commission Proposals for Speed Limiters on Commercial Vehicles. 

Royal Society for the Prevention of Accidents, Birmingham, U.K. 

The Royal Society for the Prevention of Accidents (RoSPA) accepted the request to comment on 

the Department for Transportation, Local Government and Region’s (DTLR) proposal and 

suggested that there is a need to study the effectiveness of top SLs in order to fully understand 

any safety relationships. As a result of the limited research conducted, there has not been any 

information linking the safety benefits of SLs to light trucks, buses, coaches, midi-coaches or 

minibuses. Therefore, RoSPA did not believe that the proposed measures would have a 

substantial effect on reducing roadway casualties. The real issue may be related to driving at 

inappropriate speeds within lower posted limits, which SLs do not address. Ultimately, RoSPA 

advocates for more long-term goals in which all vehicles would be equipped with intelligent SLs.

Organisation for Economic Co-Operation and Development and European Conference of 

Ministries of Transport. (2006). Transportation Research Centre: Speed Management. ISBN 

92-821-0377-3. Organisation for Economic Co-Operation and Development (OECD) and 

European Conference of Ministries of Transport (ECMT). 

This report summarizes EC Directive (92/24/ECE) on SLs, which originally required SLs on 

trucks greater than 12 tons and buses manufactured after 1987 (with the specified limits 90 and 

100 km/h, respectively). The Directive was since extended to apply to light CMVs greater than

3.5 tons and passenger vehicles with more than nine seats (ECE 2004/11). The report cites 

research supporting the regulation, which showed positive effects on emissions and fuel 

consumption through the prevention of speeding. 

The EC Directive requires SLs to be generally resistant to tampering and not to be adjustable 

while the vehicle is in motion. However, the illegal modification of SLs to allow higher speeds 

continues to be a problem. This study recommended that, in countries with no such mandatory 

system, consideration should be given to mandatory SLs for trucks and motorcoaches. However, 

they noted that even such limitations would not solve all the speed problems, especially in urban 

areas, where limitations on maximum vehicle speed would not affect compliance with lower 

speed limits. 

Repussard, J-P. (2007). Study on speed limiters. Email Correspondence. European Commission 

Directorate General Energy and Transport, Unit E3-Road Safety. 

Mr. Repussard confirmed that the first EU legislation in this area was adopted in 1992 (for 

bigger vehicles) and then, in 2002, it was extended to smaller vehicles. There is now a single 

standard for all trucks weighing a minimum of 3.5 tons and motorcoaches that contain at least 

nine seats. The author notes that the legislative text speaks to road safety and environmental 

issues almost equally (as a likely after-effect of the energy shortages of the late 1970s). The 

author also confirmed that an EC Directive such as this requires that each EU Member State 

must pass a national law implementing the terms of the Directive. 
16 

1.3.2.4 United States

Johnston, J., and Shapiro, C. (2007). Comments in Response to Notice and Request for 

Comments, Motor Vehicle and Carrier Safety Standards. Docket No. NHTSA-2007-26851. 

Owner-Operators Independent Drivers Association, Grain Valley, MO.

The authors submitted comments on behalf of OOIDA in a response to NHTSA and FMCSA 

petitions for a rulemaking by ATA, Road Safe America (a safety advocacy group), and a group 

of nine motor carriers. The rule would require the use of SLs on certain CMVs with a maximum 

speed of 109 km/h (68 mi/h) and prevent tampering with or adjusting these set speeds. OOIDA 

argued that the mandated use of SLs would decrease safety since the interaction between large 

trucks and automobiles would be increased. The authors noted that research has shown that 

automobile/light-truck drivers are more likely than CMV drivers to engage in unsafe driving 

behaviors, such as traveling at excessive speeds. Based on this research, the authors predicted 

more traffic crashes, namely entrance/exit ramp collisions, cars rear-ending trucks, and sideswipe 

crashes. In addition, the authors argued that an SL mandate would not address one of the top 

causes of large truck crashes: traveling too fast for conditions. 

Insurance Institute for Highway Safety (2007a). Good news about teen drivers. Insurance 

Institute for Highway Safety Status Report, 42. 

Recognizing the ongoing issues of large-truck crashes in which speed was a factor, some truck 

drivers, trucking companies, and industry representatives are pressuring FMCSA to require SLs.

According to the 2007 survey of passenger-vehicle drivers, 80 percent noted that speeding was a 

safety issue and 64 percent agreed that SLs, set below 113 km/h (70 mi/h), were necessary.

Many trucking companies currently limit the maximum speed of trucks without the restrictions 

of an FMCSA regulation. When purchasing new trucks, some carriers have speed limits set by 

the manufacturer prior to delivery. According to ATA, which also supports SLs, having this 

policy in place not only improves safety for the motoring public, but reduces maintenance, fuel 

use and emissions, and extends the life of truck tires. 

Insurance Institute for Highway Safety (2007b). Devices to Limit the Speed of Certain Trucks 

Request for Comments. Docket No. NHTSA-2007-26851. U.S. Department of Transportation, 

Washington, DC. 

In a memo to the administrators of FMCSA and NHTSA, the IIHS provided an argument in 

support of the implementation of SLs set at 109 km/h (68 mi/h). The primary objective of the 

document was to provide a solution to the number of fatal crashes involving trucks with other 

vehicles. According to the document, speed has a role in 23 percent of truck crashes. In addition, 

those with one or more speeding convictions within the past 3 years were involved in 24 percent 

of fatal crashes in 2005. Therefore, reducing the speed of trucks would reduce the crash rate.

The IIHS also provides other motivating reasons to implement SLs, including a reduction in fuel 

use and public support. The authors also cited the lack of law enforcement resources to adopt 

speed cameras or monitor roadways where speed is an issue. Although the memo stated that 68 

mi/h is a valid speed limit for the devices, it also concluded that it is only a starting point and 

should be further reduced in the future. 
17 

American Trucking Associations. (2009). Expanding ATA’s Safety Agenda: Executive 

Summary. American Trucking Associations, Arlington, VA. 

According to ATA’s 2009 safety policy, all class 7 and 8 large trucks manufactured after 1992 

should be equipped with SLs set at 105 km/h (65 mi/h). This ATA policy was first addressed in a 

petition to NHTSA in which ATA stated that class 7 and 8 trucks should be limited to 109 km/h 

(68 mi/h). As a complement to this policy, ATA also recommended that the SLs be tamperresistant. Since then, the topic has been studied by Congress, but a bill has not been drafted. 

1.3.3 Speed Limiter Technology and Usage 

This section examines reports discussing FOTs with speed-limiting technology, as well as motor 

carrier usage of SLs.

1.3.3.1 Intelligent Speed Adaptation

Intelligent speed adaptation (ISA) either advises drivers or intervenes to maintain the prevailing 

posted speed limit. Empirical studies, such as FOTs, for speed-limiting technologies have been 

conducted with passenger cars to evaluate ISA. Although significant safety benefits have been 

estimated for broad ISA implementation, driver acceptance in the FOTs was mixed (Bishop, 

2005; Comte et al., 2000; Svedlund, 2002). 

The OECD and ECMT (2006) were quite supportive of continuing down the path of ISA 

implementation, if shown to be cost-effective; with voluntary SLs at the initial roll-out, and 

potentially mandatory devices in the longer term. Despite the substantial activity in this domain, 

ISA is motivated by a desire to increase safety on urban, arterial, and residential roads, and 

therefore is not directly relevant to the domain of motor carriers operating on major highways. 

Bishop, R. (2005). Intelligent Vehicle Technology and Trends. Artech House, Norwood, Mass. 

This book provides an overview of current intelligent vehicle technologies and active safety 

systems worldwide, including ISA. ISA is a system that maintains awareness of the current 

posted speed limit and provides a driver with “insistent” feedback when the driver is exceeding 

the posted speed limit. Most ISA work has focused on passenger cars, to moderate speeds in 

urban and residential areas. The book reported the results of a study which found that drivers 

would support use of the system if it reduced large speeding fines. 

Three case studies are detailed. In Sweden, the author found the ISA system reduced speed 

violations and did not lengthen travel times. In addition, it was projected that if all vehicles were 

equipped with an ISA, crashes would decline by 20 percent. A second case study (conducted in 

France) found that, although drivers supported the concept of an ISA, less than one-third of 

drivers actually favored an ISA in their vehicle. In reviewing the results of another case study, 

the author noted that researchers estimated that a dynamic SL system/ISA could reduce injury 

crashes by 36 percent and fatal crashes by 58 percent. However, the author also noted that CMV 

operations are very different from automobile operations; thus, an ISA system may not be 

relevant to CMV operators that travel primarily on interstate roadways.
18 

Comte, S., Wardman, M., and Whelan, G. (2000). Drivers’ acceptance of automatic speed 

limiters: Implications for policy and implementation. Transport Policy, 7, 259-267. 

This research detailed the results of a survey of automobile drivers’ perceptions and opinions on 

the use of SLs. The study made an effort to identify the components of an SL program that most 

facilitates drivers’ acceptability. Survey respondents indicated that enforcement was more 

appropriate than SLs for targeting drivers that exceeded the posted speed limit. However, 

respondents also indicated a belief that enforcement was both expensive and ineffective and that 

SLs were the best option for discouraging excessive speeds. The authors conclude that, although 

respondents believe SLs may discourage excessive speed, drivers remain concerned over 

potential impacts on comfort and safety. 

Svedlund, J. (2002). ISA in daily life. Proceedings of the ITS World Congress. Beijing, China.

In an article published by the Swedish Road Administration (SRA), the use and acceptance of 

ISA by both passenger and CMV drivers was evaluated. Between the years 1998 and 2002, 

Sweden held an assessment of ISA implementation strategies. During this period, 1,000 systems 

were installed. It was determined that many objections exist that prevent drivers from purchasing 

the technology. However, the list of benefits outlined in the report is extensive, including: 

• Savings in fuel and maintenance costs. 

• Reducing speed-related crashes. 

• Straightforward integration with other technologies already in use. 

• Competitiveness within the industry. 

In addition, the SRA stated that working with other safety stakeholders, as well as drivers, could 

further promote the widespread use of ISA throughout Sweden and improve accident rates. 

Varhelyi, A. and Makinen, T. (2001). The effects of in-car speed limiters: Field studies. 

Transportation Research Part C, 9, 191-211. 

The study assessed the effects of SL usage for varying speed limits and the acceptability among 

its users. The SL systems were installed on 290 cars in three countries: the Netherlands, Spain 

and Sweden. In each vehicle, the SL was placed in an unobtrusive location. Cars with the devices 

traveled on roads with varying posted speed limits. It was found that the SL was most effective 

in locations where the posted speed limit was the highest. In addition, it was also noted that, in 

areas of congestion, the SLs were effective in reducing the speed variability. This was done 

through suppression of temporary speed increases. Of those that tested the SLs, 50 percent of 

drivers stated that they would accept an SL mandate.
19 

Organisation for Economic Co-Operation and Development and European Conference of 

Ministries of Transport. (2006). Transportation Research Centre: Speed Management. ISBN 

92-821-0377-3. Organisation for Economic Co-Operation and Development (OECD) and 

European Conference of Ministries of Transport (ECMT). 

As part of a larger examination of speed management trends and techniques, recent 

developments in vehicle engineering which could play an important role in improving safety are 

cited. They note the work in ISA technology, specifically the two broad ISA categories that are 

being assessed for possible wider deployment: “Informative ISA” which displays the speed limit 

and advises the driver when the limit is being exceeded, and “Supportive ISA” which intervenes 

through the vehicle speed control system to give feedback to the driver when the speed limit is 

being exceeded. 

The authors encourage progressive implementation of ISA, on a cost-effectiveness basis, given 

the potential benefits. Appropriate actions could include: 

• All new cars equipped with manually adjustable SLs (where the driver chooses the 

maximum speed), and later with informative or supportive ISA, to assist drivers in 

keeping to both static and, eventually, variable speed limits. 

• Mandatory ISA in the long term. 

• Governments and other relevant partners start developing the necessary digital speedlimit databases to support implementation of ISA. 

1.3.3.2 Safety Technology Usage by Motor Carriers 

Cantor, D.E., Corsi, T.M., and Grimm, C.M. (2006). Safety technology adoption patterns in 

the U.S. motor carrier industry. Transportation Journal, 45, 20-45. 

Cantor et al., conducted a national survey of large motor carriers operating in the United States

(n = 415) to identify safety technology adoption practices. The survey focused on 26 technology 

types generally classified into driver communication, vehicle communication, and driver 

performance/assistance technologies. Cantor et al., found that the industry is in the early stages 

of adopting safety-related technologies. The research also found that larger trucking companies 

were leading the way in technology adoption. In addition to company size, the authors found that 

large trucking companies that operate over larger geographic areas were most likely to adopt 

these technologies. These companies had the organizational resources to support the adoption 

and use of safety-related technologies. However, the authors also found that commodity had little 

impact on a carrier’s likelihood to use these technologies. 

McDonald, W., and Brewster, R. (2007). Survey of Motor Carriers on Issues Surrounding the 

Use of Speed Limiting Devices on Large Commercial Vehicles. American Transportation 

Research Institute, Arlington, VA. 

As part of a larger effort to determine the consequences of the industry's increasing use of SLs 

(and subsequent increase in truck/automobile interactions), a convenience survey (n = 240) of the 

industry was conducted to identify the ideal speeds for maximizing different operational 

objectives such as productivity, safety, and fuel economy. Survey respondents represented all 
20 

major sectors of the industry and carrier sizes. The study found that nearly two-thirds (63 

percent) of motor carriers use SLs on at least a portion of their fleet. Use of SLs was more 

prevalent among larger carriers. In addition, the study found that larger carriers were more likely 

to adopt lower maximum speeds than were smaller fleets. Carriers that did not use SLs believed 

SLs actually decreased safety by increasing the interaction between large trucks and 

automobiles. The average maximum speed for respondents was 111 km/h (69 mi/h). SL settings 

were most often based on the posted speed limits in the areas of operation (57 percent) and fuel 

considerations (15 percent).

Owner-Operator Independent Drivers Association. (2007). Speed Limiter Survey Results 

Final Report. Owner-Operator Independent Drivers Association, Grain Valley, MO.

In 2007, OOIDA sent an SL survey to all of its members. Of the 3,422 respondents, each 

submitted answers to questions about SL preferences as well as advantages and disadvantages to 

having one installed. More than 60 percent of all those who completed the survey indicated that 

they drove for companies in which SLs were required. Although many noted that having the SL

was part of a trade-off to having a higher wage and benefits, more than 80 percent stated that 

they would rather drive for a carrier that did not require an SL. According to drivers, this was 

due to the fact that it reduced the driver’s ability to complete a delivery on time, especially when

traveling in congested areas. In addition, more than 80 percent admitted that, in areas where the 

posted speed limit was lower than the SL setting, they traveled at faster rates than was legal.

Transportation Research Board. (2008). CTBSSP Synthesis 16: Safety Impacts of Speed 

Limiter Device Installations on Commercial Trucks and Buses. Transportation Research Board, 

Washington, DC. 

A comprehensive literature review synthesis was completed to understand and examine research 

related to SLs within Australia, Europe, and North America. As a component of the synthesis, 

researchers used the literature findings to develop and distribute an SL survey to the CMV 

industry. The survey was comprised of 27 questions and distributed to approximately 1,500 

recipients with a response rate of 7 percent (103 responses). 

Survey results indicated that the majority of respondents (88 percent) believed that CMV drivers 

tended to increase speed while driving where the posted speed limit was below that of the SL. 

However, findings also suggested that driver behaviors were more likely attributable to the 

speeding rather than the SLs themselves. More than half of the respondents (56 percent) said that 

SLs were either successful or very successful in reducing crashes. Similarly, 64 percent indicated 

that speeding violations were successfully reduced. A large portion (77 percent) suggested that 

the SLs had neither a positive nor negative result on driver hiring or retention. Almost all 

respondents said that SLs have not had a negative effect on productivity (96 percent) or safety 

(96 percent).

1.3.4 Safety Results from Implementation

The key aim of this section was to establish the level of safety-relevant research results regarding 

the implementation of SLs. Although analytical progress has been made in recent years, 

empirical results are still lacking.
21 

National Highway Traffic Safety Administration. (1991). Commercial Motor Vehicle Speed 

Control Safety. Report to Congress, DOT-HS-807-725. National Highway Traffic Safety 

Administration, Washington, DC. 

In a study conducted by NHTSA, the effect of SL use on truck crashes was examined. According 

to the study, due to higher interstate speed limits of 105 km/h or more (65 mi/h or more), a large 

percentage of SL trucks would still be driving at the maximum posted speeds. However, most 

(95 percent) single-unit truck crashes occur on roads where the speed limit is less than 105 km/h 

(65 mi/h). The authors argue that this creates a lack of authority for the argument that SLs would 

be needed to reduce speeds and decrease the number of crashes on most roadways. 

Different types of SLs were also examined in this report to determine possible benefits. One 

issue brought to the forefront was speeding while traveling downhill. Since many SLs available 

to fleets only measure engine speed, it is possible for drivers to travel at speeds far higher than 

105 km/h (65 mi/h) downhill. In addition, although SLs are marketed as tamper-resistant, it is 

possible for drivers to alter the devices. Therefore, the authors concluded that public information 

and educational programs may be the most effective approaches to obtaining SL compliance. 

Repussard, J-P. (2007). Study on speed limiters. Email Correspondence. European Commission 

Directorate General Energy and Transport, Unit E3-Road Safety. 

Mr. Repussard confirmed that there has been no EU-wide study as to the safety impact of SLs. 

When the legislation was being passed, he states that supporting documents quoted “some 

studies” pointing to the positive/negative impacts (not further referenced) and also quoted similar 

comments from some Member States (Denmark, Spain, Luxembourg, and the United Kingdom). 

He noted that the road accident rate for trucks has been decreasing faster than the general vehicle 

population but also cautions that it is not possible to quantify the specific contribution of SLs due 

to the variety of factors.

Transport Canada. (2008b). Safety Implications of Mandated Truck Speed Limiters on 

Canadian Highways. Transport Canada No. TP-14807. Transport Canada, Ottawa, Canada.

The Safety Implications Study aimed to determine whether SLs would reduce the risk and 

severity of truck crashes. It also assessed the safety impact of speed differentials and car-truck 

interactions in a SL environment. In the study, traffic simulations for three highway scenarios 

were conducted in addition to a case study of a Canadian freeway section. 

Simulation results showed that truck SLs set at 105 km/h (65 mi/h) increase safety in 

uncongested traffic flow. This is true for all geometric configurations, especially straight 

segments. If SLs are set at 110 km/h, the safety gains are reduced in uncongested traffic. The 

simulations showed that the maximum safety gains were obtained when SLs were set at 90 km/h

(56 mi/h) in uncongested traffic. 

Specifically for the freeway case study, which was applied to the Eastbound Queen Elizabeth 

Way (QEW) in Toronto, the study concluded that the introduction of SLs set at 105 km/h yielded

statistically significant safety gains as compared to the base case of no mandatory SLs. Over 30 

simulation runs the average safety increase was 16 percent, with positive safety gains observed 

in 21 of the runs. 
22 

There are cases in which the crash risk increases when traffic volumes and truck ratios increase. 

For example, for traffic volume above 1,250 vehicles per hour per lane, SL trucks cause more 

vehicle interactions to take place, which leads to a reduction in safety due to lack of space to 

adjust speed or lane. This is especially true for segments with increased merging and lane-change 

activity, due to on and off ramps. The authors note that this finding is based on simulation of 

uncongested traffic. In the real world, as traffic volumes approach capacity, the vehicle speeds 

will be dominated more by congestion, such that the SL limited vehicles will be operating below 

the speed limit and, therefore, the SLs would not be expected to have an effect on safety. 

Nevertheless, they do acknowledge that, given the volume of trucks on some Canadian freeways 

and traffic volume overall, this result could present some “safety challenges” with the 

introduction of SLs.

The authors noted that, although it is logical that crashes would be reduced following a lowering 

of the maximum speed limit for all vehicles in the traffic stream, the challenge is to determine 

the effect of a strategy that targets one group of vehicles (trucks) and not another (cars). The 

related implications for altering speed differentials in the traffic stream with possible increases in 

traffic turbulence. Increased turbulence would be expected to increase the number of crashes and 

crash severity. The authors suggest speed variance, rather than mean speed, explain the 

likelihood of crashes on freeways. And, speed variance provides a better explanation for 

“turbulence” in vehicular flow by increasing lane change behavior and acceleration/deceleration 

profiles and hence increases in traffic conflicts and crashes.

Transport Canada. (2008a). Final Report: Learning from Others: An International Study on 

Heavy Truck Speed Limiters. Transport Canada No. TP-14810. Transport Canada, Ottawa, 

Canada. 

This study was conducted as part of a comprehensive study on SL impacts for trucks operating in 

Canada. Australia, Sweden, and the United Kingdom were selected for the international 

assessment. Each participating jurisdiction’s SL legislation, national compliance approach, 

enforcement methods/regime, measures of effectiveness, and summary views from road transport 

stakeholders were documented. 

Although the status of SL implementation in these countries has been covered in other sections 

of this literature review, it is instructive to review what the authors of this report considered to be 

the most salient conclusions from this investigation. They note that the European Commission 

and Australia implemented SL legislation based on concerns over road safety due to a high 

incidence of crashes involving heavy trucks and concerns over the environmental impact of fuel 

emissions due to heavy-vehicle speeding. In both cases, no research or empirical studies were 

done prior to enacting the legislation to justify the implementation of the SL requirement. 

Furthermore, the authors note that 10 years later, no empirical studies have been conducted in 

any participating jurisdictions to directly link the use of SLs with improvements in road safety. 

Additionally, they cite a lack of research on the safety impacts of truck-car speed differentials 

due to SL trucks. The study concluded that it is difficult to predict the potential road-safety

impacts of an SL mandate in Canada.

Road-safety concerns as a result of the SL requirement have been noted by U.K. and Swedish 

officials. This problem resulted in U.K. officials restricting heavy trucks to the inside lane of 
23 

motorways and Swedish officials restricting truck overtaking on some sections of the highway. 

In the United Kingdom, the inside lane restriction may have addressed the heavy-truck 

overtaking issue, but government officials acknowledge this may have created other problems in 

terms of other traffic being able to easily access exits or merge onto motorways. 

Transport Canada. (2008c). Speed Limiter Case Study and Industry Review. Final Report.

Transport Canada No. TP-1002769. Transport Canada, Ottawa, Canada. 

This case study, involving two large Canadian carriers, was conducted to document the benefits 

and experience of SL usage within the Canadian trucking industry. Two large trucking firms 

were selected through their respective trucking associations, one for-hire carrier and one private 

carrier. Both were based in Ontario and together have about 400 power units on the road. Both 

firms have operated with SLs since the mid 1990s. These fleets believed SLs had a significant 

positive impact on safety, fuel savings, and other maintenance costs. 

Both carriers believed that their lower fleet speed has resulted in an improved safety record. 

About half of their reported crashes were low-speed (on company property), resulting in property 

damage only. For the remaining crashes, the study noted that there was no evidence of vehicles 

rear-ending trucks in these fleets. More generally, the crash data analyzed do not show any 

evidence that SLs are contributing to the occurrence of crashes. Both carriers believe that their 

speed control policy has resulted in a reduction in crashes, but no empirical data supports this 

contention. 

Drivers from these fleets were interviewed in the study. The drivers did not believe the speed 

control policies created any significant operational or safety concerns. Further, they generally 

accepted the speed control policy and expressed satisfaction with their jobs. 

Thiffault, P. (2009a). Safety implications of mandating speed limiters for motor carriers in 

Canada. Currently unpublished. Transport Canada, Ottawa, Canada. 

This document reviewed the scientific literature to rebut the position that SL implementation can 

reduce safety due to alleged safety risks of the resulting speed differentials. Regarding absolute 

speed, the author cites literature to argue that absolute speed increases the difficulty of the 

driving task, which is particularly true for trucks, as speed exponentially increases an already 

problematic braking distance and complicates tracking in emergency situations. Absolute speed 

increases crash risk and exponentially increases crash severity. 

Regarding speed differential, the author cites additional literature to argue that, although there is 

a consensus that faster moving traffic increases risk, the risks associated with slower traffic are 

far from being conclusive. Although speed differential only contributes to a limited portion of 

road crashes, absolute speed increases crash risk and crash severity for all types of crashes. The 

potential impacts of SL implementation on the speed differential are complex. This would 

increase the differential between trucks and speeding traffic. However, the increase in the 

differential between mean truck speed and mean traffic speed is likely to be small. He also notes 

that SLs would reduce speed differentials among trucks, SLs for trucks would decrease the 

overall mean speed of traffic, and SLs would prevent speed variances resulting from speeding 

trucks overtaking traffic traveling at the posted speed limit. 
24 

The author concludes that the literature on the speed differential and absolute speed issues 

suggests that: SLs would decrease the crash risk of trucks currently traveling faster than 105 

km/h (65 mi/h), as well as the severity of their crashes when they do occur. SLs for trucks would 

generate some positive effects on the speed differential because this would decrease the variance 

within the trucking population and prevent trucks from overtaking cars traveling at or around the 

speed limit. There is no evidence that slightly increasing the mean speed differential by slowing 

down trucks to 105 km/h (65 mi/h) will increase crash risks for trucks; and the increase in 

interactions between speeding cars overtaking speed-limited trucks and the associated risks are 

uncertain, calling for more research in this area. The overall conclusion was that the scientific 

literature does not provide a justification to reject an SL mandate on the basis of safety risks. 

Organisation for Economic Co-Operation and Development and European Conference of 

Ministries of Transport. (2006). Transportation Research Centre: Speed Management. ISBN 

92-821-0377-3. Organisation for Economic Co-Operation and Development (OECD) and 

European Conference of Ministries of Transport (ECMT).

This report noted that SLs can have some potentially negative impacts on safety. It cited results 

of traffic flow measurements on major truck routes which showed that road capacity (vehicles 

per hour) could deteriorate over time as the proportion of SL trucks rises (as SLs increase the 

time required for equipped vehicles to overtake other traffic). Based on the literature, there is

concern about the potential for increases in the overtaking of SL trucks on two-lane roads, which 

could lead to more truck-related crashes. 

The report also points out that SLs do nothing to reduce speeding on roads with posted speed 

limits below the set speed, nor on downgrades steep enough to cause free-rolling. The authors 

believe that, in some cases, truck drivers may be tempted to always reach the maximum speed set 

by the SL. Nevertheless, the report concludes that SLs have contributed significantly to reducing 

accidents involving trucks. Further, there are many countries where SLs are not used and 

consideration should be given to mandatory SLs for trucks and motorcoaches.

1.3.5 Other Benefits Attributed to Speed Limiters

Examinations of non-safety benefits relating to SLs have focused mainly on fuel economy. Fleet 

operators clearly have the perception that SLs can increase fuel economy. This section describes 

other benefits attributed to SLs. 

Transportation Research Board. (2008). CTBSSP Synthesis 16: Safety Impacts of Speed 

Limiter Device Installations on Commercial Trucks and Buses. Transportation Research Board, 

Washington, DC. 

This literature review synthesis was completed to understand and examine research related to 

SLs within Australia, Europe, and North America. As a component of the synthesis, researchers 

used the literature findings to develop and distribute an SL survey to the CMV industry. The 

survey was comprised of 27 questions and was distributed to approximately 1,500 recipients with 

a response rate of 7 percent (n = 103). The survey found that, in operational terms, SL users 

consider SLs to be either “successful” or “very successful” in reducing tire wear (44 percent) and 

increasing fuel economy (76 percent). Regarding driver hiring and retention, 77 percent of 

respondents see SLs as a neutral factor. 
25 

Transport Canada. (2007a). Final Report: Environmental Benefits of Speed Limiters for Trucks 

Operating in Canada. Transport Canada No. TP-14811. Transport Canada, Ottawa, Canada. 

This study quantified the potential annual diesel fuel savings and GHG reductions from a 

national SL mandate in Canada. The study concluded that 228 million liters of fuel could be 

saved annually, which is 1.4 percent of the total diesel fuel that was consumed by all road 

vehicles in Canada in 2006. The annual GHG savings are estimated at 0.64 megatons, with 

Ontario and Quebec combined accounting for 64 percent of the estimated national savings. 

Hammerstrom, U., and Yahya, M. (2007). Speed Regulator and Fuel Consumption of Heavy 

Trucks with Trailer—Result of Reducing Maximum Speed from 89 to 85 kph. Swedish National 

Road and Transport Research Institute, VTI notat 32-2006. 

Given that trucks in Sweden with a GVM of greater than 12 tons have been required to be 

equipped with an SL since 1992, the authors worked with CMV fleets to investigate the effects 

of changing speed regulator settings from 89 km/h (55 mi/h) to 85 km/h (53 mi/h). Test results 

were based on 12 trucks from 5 companies. Due to inconsistent methods, the results were 

somewhat ambiguous, showing an increase in fuel consumption, with a maximum change of 3 

percent. The researchers noted that data were not collected for other factors at play—such as 

road type and load—which could have affected fuel consumption. The report concluded that 

lowering the speed setting by 4 km/h (2 mi/h) would result in an estimated reduction in fuel 

consumption of less than 1 percent. 

Transport Canada. (2007b). Final Report: Trade and Competitiveness Assessment of Mandated 

Speed Limiters for Trucks Operating in Canada. Transport Canada No. TP-14813. Transport 

Canada, Ottawa, Canada. 

This assessment investigated the potential trade and competitiveness impact of mandating SLs 

under two scenarios: an Ontario/Quebec mandate and a national mandate. The general 

conclusion is that there would likely be very few competitiveness issues because the majority of 

large North American fleets already use SLs. The concerns about an SL mandate that do exist 

come from smaller North American fleet operators and owner-operators, who typically either 

don’t use SLs or have them set at higher speeds. These operators cite safety concerns, indicating 

they would avoid operating in speed-limited jurisdictions. There were also concerns that SLs 

would negatively affect driver recruitment and retention; however, fleet managers contended that 

drivers are more likely to consider pay, monthly mileage, and fringe benefits as the dominant 

factors here. 

The assessment also included a cost analysis to determine the potential trade-off between 

productivity benefits and increased costs. This analysis concluded that increased fuel costs from 

operating at speeds higher than 105 km/h (65 mi/h) are greater than any productivity gains. An 

overall cost savings of 2 percent was found when operating at 105 km/h (65 mi/h) compared to 

113 km/h (70 mi/h), and a 9.5 percent cost savings was found when compared to operating at 

121 km/h (75 mi/h). The total fuel savings from a national mandate was estimated at 228 million 

liters annually. Expressed in monetary terms, this could be roughly $200 million annually. 
26 

1.3.6 Literature Review Summary 

Based on crash data from several studies, speeding was one of the primary factors in motor 

vehicle crashes and this risky behavior was compared to driving with a BAC of 0.08. 

Documented disadvantages to speeding included a possible increase in transloading, a higher 

probability of being involved in a crash, and an increase in the severity of the crash. Several 

sources used a mathematical analysis to assess the relationship between crashes and speed, and 

found that higher speeds increase crash-related fatalities.

Speed is clearly a factor in crashes, but the literature is mixed in terms of the relationship of 

speed to posted speed limit. Some sources note that crashes occurring when the vehicle was 

traveling above the posted speed limit are minor compared to the case of traveling too fast for 

conditions; however, other sources note a preponderance of interstate-related crashes in which 

the vehicle was exceeding the speed limit. Although the literature review did not yield any 

citations of empirical studies specifically assessing the safety effectiveness of SLs on long-haul 

trucks, estimates of the potential benefits have been made. SLs have been mandated in Europe 

for more than 10 years, and U.K. data show that the crash involvement rate for SL trucks fell 26 

percent between 1993 (when mandated) and 2005. U.K. authorities noted that other contributing 

factors may have influenced the decline, but concluded that SLs played a significant role. Other 

countries, such as Australia, have SL regulations in place and estimate that the posted speed limit 

reduction may decrease large truck-involved crashes by 29 percent. SLs cannot address speeding 

on roads with speed limits lower than the SL setting, and the literature shows that speeding 

continues to be a problem in these situations. 

In 2009 SLs were mandated in the Canadian provinces of Ontario and Quebec. In the United 

States, organizations such as ATA support legislation for SLs, but other organizations, including 

OOIDA, do not support the use of SLs (citing a possible increase in the interaction between cars 

and large trucks; thus, higher crash levels). There is still a debate in Congress as to the details of 

such a law and whether it should be enacted. 

The potential for an increased crash risk due to speed variances created by SLs on trucks was 

addressed in various simulations, showing a significant safety increase for typical conditions.

Some sources report that SLs decrease speed variances by minimizing truck-to-truck speed 

differentials and trucks passing cars. Assertions that earlier literature points to a safety decrease 

due to SLs must be examined carefully because these studies address either extreme speed 

variations or highly general cases (which may not apply to the specific conditions created by SL 

trucks). Furthermore, a strong argument can be made that absolute speed matters more than 

speed differentials when assessing the total safety picture. 

Sources noted many advantages to SLs, such as a reduction in fuel spending, decreasing speedrelated crashes and violations, and cohesiveness with already equipped technologies. Traffic 

effects were noted as a concern in some areas, due to the long distance required for one SL truck 

to overtake another (and the resulting traffic backlog). This problem resulted in U.K. officials 

restricting heavy trucks to the inside lane of motorways. The literature reviewed here clearly 

shows that SL usage is very high in other parts of the world; however, supporting empirical data 

are minimal. Many fleets support use of SLs because of operational efficiencies as well as some 

evidence of safety benefits.
27 

1.4 EVALUATION OF SPEED LIMITER IMPLEMENTATION IN COMMERCIAL 

TRUCKING

This section of the report addresses technologies and techniques in past SL applications, and 

provides information on current SL devices and manufacturers. Key areas of investigation 

included the scope and extent of SL applications and costs of implementation. The information 

contained within this section is the result of interviews with fleet operators, manufacturers, and 

industry organizations, and a review of relevant literature. Specifically, to bring a range of 

perspective to the discussion, Representatives across a variety of industries and functions were. 

For general background information, those interviews included an industry trade council, a truck 

OEM, and an engine OEM. For questions related more specifically to fleet operations, both 

private and for-hire fleets across a range of fleet sizes and industry segments, including truckload 

(TL), less-than-truckload (LTL), and specialized fleets were contacted. Due to the sensitive 

nature of these conversations, all responses have been made anonymous and incorporated into 

the summary below. For motorcoaches, information and perspectives were received from the 

motorcoach industry via contacts with the American Bus Association and the United Motorcoach 

Association. 

1.4.1 Speed Limiter Technology: Status and Availability in Heavy Trucks

Current SL technology is mature technologically. SLs are standard equipment on new trucks and 

have been for some time, with the core technology built into the ECM. No evidence was found 

of SL availability in the aftermarket. Historically, SLs existed as distinct, mechanical parts.

These parts generally did not function very well, and were fairly easy to bypass. Over time, the

trucking industry moved toward electronic engine management systems for a number of reasons, 

including durability and lower maintenance costs. Newer trucks are built to be vertically 

integrated, with significant interaction between all the system components. 

An important part of this new, vertically integrated system was the ECM. Although SLs are still 

represented as separate and distinct parts, maximum speed is simply a setting on the ECM 

contained within every engine. There are a number of ECMs located throughout the vehicle, each

governing different systems (e.g., brakes, engine, etc.). The ECM that governs the engine has a 

number of parameters that can be set, including maximum speed. As the overall system became 

more complicated in recent years, the ECM followed, with more and more settings and 

parameters. Again, these changes were driven by system needs as a whole, and maximum speed 

was simply one of the first settings that came along. Some of these settings can be altered by a 

fleet using a simple PC service tool connected to a standard data bus (e.g., maximum speed, etc.), 

and some settings are designed to be set by the manufacturer and not modified by the owner 

(e.g., those relating to Environmental Protection Agency [EPA] standards). 

Therefore, since at least 1994, every large truck engine comes with the ability to limit speed. In 

some cases, the engine may arrive from the OEM preset, or the setting may be left for the fleet to 

determine. Although the ECMs themselves may differ in settings available and calculation 

methods (e.g., idle time reporting) across different engine OEMs and truck manufacturers, the 

maximum speed setting is straightforward and nearly identical across these different segments. 
28 

1.4.1.1 Engine Manufacturer Findings

The ECM is a computing platform running various software applications; the SL is one feature 

within this software. The software generally contains a number of different speed control and 

speed limit features designed to maintain a stable engine or vehicle speed. These features include 

power takeoff (used to drive auxiliary devices, like pumps, augers, or generators at a fixed speed) 

and cruise control (used to maintain a constant vehicle speed). Engines typically have one 

minimum SL for low idle. Engine manufacturers often allow end users to adjust the low-idle set 

point within a prescribed range. Generally lower speeds conserve fuel, and higher speeds reduce 

vibrations. The adjustable range allows flexibility to avoid vibrations while minimizing fuel 

consumption. 

Engines have several maximum SLs, including: high idle governor, road speed governor, and a 

number of other proprietary options, depending on the manufacturer. The high-idle governor 

limits the maximum engine speed. This limiter sets the maximum engine speed boundary for the 

engine. The boundary is set by the engine manufacturer for a specific engine rating and cannot 

be changed or adjusted. This boundary may be set to limit maximum power or to avoid overrevving engine components. The road speed governor limits the maximum vehicle speed.

Typically, the limiting value is stipulated by the end user and is trimmed by the truck OEM or 

end user. End users can use this feature to comply with legislated maximum vehicle speeds. 

Various other proprietary SL applications exist, although the industry's use of these applications 

can change as carriers seek to modify their employees’ driving behaviors to fully realize the 

operational benefits of modern day equipment. Efforts to document these changes are challenged 

by the diversity of the industry, the industry’s response to external factors (e.g., high fuel prices), 

and the many options available to carriers to modify various SL and engine settings.

The speed-related features that can be trimmed by the end user are generally defined in the 

vehicle sales specification, which means an end user can order the features trimmed by the OEM.

Engine OEMs also offer software packages that allow fleets to trim these settings at will. In 

many cases the end user may decide to alter trim settings after gaining experience with the 

features. ECMs are generally prepared for engine OEMs by a supplier and are fairly specialized.

Thus, engine OEMs will receive the ECM as one sealed part/component. Then, OEMs mount the 

ECM on the outside of the engine skin, due to heat concerns. In fact, some engine OEMs will 

even put a coil of tubing running diesel fuel in contact with the ECM to serve as a cooling 

mechanism. Note that the software accompanying the ECM is generally proprietary, and the 

features described above are built within the software. In some cases, engine manufacturers will 

label the software with a part number, complete with subassemblies. The software is also fairly 

modular in design, enabling engine OEMs to mix and match abilities as needed. 

1.4.1.2 EMA and TMA Comments to Transport Canada 

Based on a request for information regarding SL use and technology, comments from the TMA 

and the EMA (prior to association merger) were published by Transport Canada (2007). TMA 

represents the following companies: Ford Motor Company, Freightliner Trucks, General Motors 

Corporation, International Truck and Engine Corporation, Isuzu Commercial Truck of America, 

Inc., Kenworth Truck Company, Mack Trucks, Inc., Peterbilt Motors Company, Sterling Truck 

Company, Volvo Trucks North America, and Western Star Trucks. EMA represents all 
29 

manufacturers of heavy-truck engines, including: Caterpillar Inc., Cummins, Inc., Daimler 

Trucks North America LLC, MTU Detroit Diesel, Inc., Navistar, Inc., and PACCAR Inc. 

SLs are available options on nearly all trucks equipped with electronically controlled engines, 

and enable fleet operators to optimize their fuel economy or other business factors. Further, 

nearly all model year 1995 and newer diesel engine-equipped trucks (with GVM rating greater 

than 11,000 kg) manufactured in North America are equipped with ECMs that have the 

capability to be programmed to limit the vehicle's road speed. One caveat is that some model 

year vehicles as new as 2003 were built with mechanically controlled engines that do not include 

an electronic vehicle SL system. TMA states that they are not aware of any manufacturers that 

make an electronic road SL for a mechanically controlled diesel engine today. 

TMA describes the SL implementation as follows: a transmission output shaft rotational speed 

input signal is transmitted to the engine ECM. In order to make use of those data, other variables 

must be defined in the ECM, including transmission output shaft pulses per revolution, tire 

rolling radius, and rear axle gear ratio. EMA notes that the engine ECM is calibrated by the 

vehicle manufacturer, dealer, and/or owner to reflect the choices of tire size, rear axle ratio, and 

transmission top gear ratio for the road speed limit function to operate correctly. Heavy duty 

vehicle speedometers also use this calibration of the vehicle speed signal to display vehicle speed 

to the driver. EMA emphasizes that the accuracy of the SL setting is dependent upon the accurate 

capture of these variables (which are unknown at the time of engine manufacture). 

There are several industry standards incorporated into engine ECMs that relate to the vehicle 

speed sensor signal, data, and diagnostics provided by SL systems. TMC RP 123 defines a 

convention for speed signals. Signals from transmission drive shafts are standardized at 16 pulses 

per revolution, but many engines do not require that the signal contain exactly 16 pulses and 

these can use other conventions. Multiplexed signals from an electronically controlled 

transmission (transmission output shaft speed) and the antilock brake system (wheel speed) are 

also used to provide the raw speed signal to the engine, typically using the SAE J1939-71 

standard. 

Vehicles can coast faster than their vehicle speed limit setting on downhill grades. Several

manufacturers have recognized the importance of maintaining momentum in rolling terrain and 

provide a way to achieve a modest increase in speed over the set limit on a downhill slope to 

provide additional momentum for the next uphill slope. This concept mimics the engine speed 

overrun performance that was typical of mechanically governed engines, and provides smooth 

transitions between fueled and non-fueled engine operation at highway speeds. 

A number of manufacturers offer software that allows the driver to temporarily override the SL. 

In some cases, the vehicle owner sets the allowable over-speed, and other approaches allow a 

maximum variation around the specific speed setting. There also may be a driver reward feature 

available where the vehicle owner allows a higher speed limit for drivers with good fuel 

economy habits. Another option allows the cruise control limit to be set higher than the specific 

SL value to encourage the use of cruise control. A few manufacturers offer the option for driver 

adjustment from inside the cab. 
30 

Although many owners possess the software that allow them to change the SL settings as 

desired, other operators do not have this ability and must rely on the dealer to access the settings 

if changes are desired. Generally, this service is not performed without an associated charge. The 

cost of the software and hardware to enable changes by the owner is estimated to be between 

$500 and $1,000. Fleets that purchase large quantities of engines and vehicles often get the 

benefit of the software and hardware as part of their purchase. This is usually not the case with 

purchases of single vehicles and engines.

The speed setting cannot be adjusted without the proper OEM-supplied equipment (interface, 

software, etc.). The speed limit setting is secured with a password unique to the vehicle that is 

given to the owner of the vehicle. The owner of the vehicle can then change the password as 

desired. The vehicle owner controlling and limiting access to the password is a key principle in 

preventing improper changes. The industry associations contend there has been no need to take 

extraordinary steps to make the SL setting tamper-resistant. These associations state that 

tampering with the vehicle speed limit setting or one of the associated parameters is not believed 

to be commonplace. 

1.4.2 Speed Limiter Technology: Status and Availability in Motorcoaches

Prior to the advent of electronic controls, SLs in the form of mechanical flyweight governors 

were standard for motorcoaches. Originally, the primary function of the SL was to prevent 

engines from exceeding their maximum RPM rating, as well as in limiting the vehicle’s 

maximum speed. However, since the mechanical SL was very easy to tamper with, engine 

manufacturers decided to make the erasable programmable read-only memory (EPROM) on the 

electronically controlled engines adjustable only by the manufacturer. This eliminated tampering, 

so that the vehicle’s top speed was limited and the manufacturer was better able to contain 

warranty costs. 

Electronically controlled engines have been in use since the mid-1980s. As such, the vast 

majority of the commercial motorcoach fleet is equipped with these. In terms of equipment, the 

current situation with motorcoaches is much the same as with large trucks (since they use the 

identical engines and control technology). Speed limiting is a function of the factoryprogrammed EPROMs and operators have the option to designate the factory set speeds and do 

so for safety, fuel economy, and engine/powertrain life. After delivery, operators optionally have 

the ability to adjust the maximum speed via a password-protected protocol. 

1.4.3 Speed Limiter Usage: Scope/Operational Techniques in Heavy Vehicles

1.4.3.1 Speed Limiter Use

OOIDA research indicates that the overwhelming majority of small carriers (20 trucks or less) do 

not employ SLs and this represents 96 percent of the U.S. trucking industry (OOIDA, undated). 

Note that this is the fraction of carriers and not trucks. Most trucks are operated by large carriers, 

with approximately 50 percent of the trucks operated by 0.5 percent of the carriers (Motor 

Carrier Management Information System Census file). In a survey conducted by the OOIDA 

Foundation (2007), questionnaires were sent to the company driver portion of their membership 

(approximately 15,000 drivers). Survey responses from 3,422 drivers represented 2,080 trucking 

companies. The results indicated that 60.8 percent of trucking companies use SLs. 
31 

A survey (McDonald and Brewster, 2007) found that overall installation rates of SLs were 63 

percent for motor carriers, which are comparable to rates identified in the OOIDA study for 

company drivers. 

In a convenience survey of carriers conducted by TRB (2008), 79 percent of respondents 

reported using SLs compared to 64 percent of the TL sector, 54 percent from the LTL sector, and 

58 percent from the specialized sector. Overall, 63 percent of carriers reported using SLs. These 

carriers that used SLs accounted for 77 percent of the trucks, a testament to the increased 

likelihood among larger carriers to use SLs. Eighty-two percent of respondents used SLs in at 

least some of their vehicles (averaging 90 percent). Of the 82 percent of respondents who 

indicated using SLs, 95 percent used factory-installed SLs and have done so for an average of 

11.5 years.

In summary, OOIDA contends that owner-operators typically do not employ SLs. For companyowned trucks, the surveys conducted by OOIDA and ATRI, and the TRB study indicate that 60 

to 63 percent use SLs, with variations across sectors. The investigation for this report yielded 

higher estimates for fleets.

1.4.3.2 Motivation and Cost 

In the TRB (2008) study, almost 56 percent of respondents indicated SLs were either 

“successful” or “very successful” in reducing crashes. In operational terms, SL users believed 

that SLs were either “successful” or “very successful” in reducing tire wear (44 percent) and in 

increasing fuel economy (76 percent). Almost 96 percent of respondents indicated SLs did not 

negatively affect safety or productivity. In the investigation for the current report, every fleet 

interviewed indicated some combination of fuel conservation and safety as the primary 

motivation in activating SLs. Additionally, one fleet identified significant benefits in terms of 

decreased maintenance needs and decreased tire wear. Every fleet interviewed agreed that the 

cost to implement SLs was negligible. In fact, it appears that external costs only accrue to fleets 

which require dealers or maintenance centers to adjust the SL settings. In this situation, the fleet 

is required to pay for the needed labor. Often, larger fleets perform this work in-house. 

1.4.3.3 Speed Setting and Operational Approach 

According to comments submitted to Transport Canada by EMA and TMA, significant numbers 

of carriers choose to set the SL at or below 113 km/h (70 mi/h). They referenced a survey which 

indicates that more than 50 percent of Class 7 and 8 trucks sold have this SL setting. However, 

this may not be especially meaningful, given that the operator can change the setting after 

delivery of the vehicle. The OOIDA Foundation Survey (2007) found that 6.3 percent of SLs 

were set at 97 to 100 km/h (60 to 62 mi/h), 50.6 percent were set at 101 to 105 km/h (63 to 65 

mi/h), and 43.1 percent were set at 106 to 109 km/h (66 to 68 mi/h). Here it should be noted that 

the response categories in the survey were limited to a maximum of 109 km/h (68 mi/h) as the 

survey was specifically addressing the Canadian SL regulations under consideration at that time.

Therefore the survey provides no indication as to the number of companies that have SLs set 

above 68 mi/h. 

Generally, larger fleets appeared to have more standardized policies regarding the use of SLs.

For instance, one large fleet set the maximum speed limit at 105 km/h (65 mi/h) for the entire 
32 

fleet. Regardless of size, if a fleet used a policy concerning SLs, then every truck in the fleet was 

required to have the maximum speed setting enabled. Of the fleets interviewed in the current 

report, none indicated having programs in place that allowed qualifying drivers to operate 

vehicles at higher speeds. Additionally, none of the fleets interviewed used aftermarket parts in 

their efforts to limit speed. 

Although driver tampering may have been a problem with mechanical systems, the problem 

seems to have been largely alleviated by new software-based systems. Every fleet interviewed 

used a password to secure the maximum speed setting. In one case, a fleet recounted how a 

driver had guessed the password and paid an engine maintenance center to reconfigure the 

maximum speed setting. However, such reconfiguration leaves an “electronic trail” which 

exposed the offending engine maintenance center, and the offending driver was reprimanded. 

In the TRB (2008) study, survey results indicated that SL settings on the SLs were within a fairly 

narrow range of about 6 km/h (4 mi/h) (e.g., 105 to 111 km/h or 65 mi/h to 69 mi/h). Most 

respondents (90 percent) selected safety as the primary consideration for determining the set 

speed on their speed limiters, followed by fuel mileage (69 percent) and posted speed limit (56

percent). Respondents were evenly split in terms of setting a different cruise control speed limit 

from the on-pedal (non-cruise control) speed limit. The majority (56 percent) of respondents did 

not use this practice. The difference in set speed between cruise-control and on-pedal (non-cruise 

control) SL was not noteworthy. The mean setting for the cruise-control speed limit was 106 

km/h (65.6 mi/h) and 108 km/h (67.2 mi/h) for on-pedal operations (a difference of only 2.6 

km/h or 1.6 mi/h).

About 12 percent of respondents in the TRB (2008) study operated with variations in the top 

speed of the SL based on driver performance. For drivers considered inexperienced or risky, 

speed settings were reduced. For example, one company used a policy in which all students were 

set at 105 km/h (65 mi/h); veterans were set at 113 km/h (70 mi/h); and if a driver was put on 

probation for any safety-related reason, he/she was set at 105 km/h (65 mi/h). 

1.4.4 Speed Limiter Usage: Scope and Operational Techniques in Motorcoaches 

Most commercial motorcoach fleets operate with SLs set at 116 km/h (72 mi/h); however, many 

companies have settings below 113 km/h (70 mi/h). Use of SLs is motivated primarily by safety, 

as well as savings in fuel cost and maintenance. Since the SL capability is a standard feature on 

all engines used in the industry, there is no cost increase to the operators above the initial vehicle 

price. 

1.4.5 Future Trends

Since limiting speed happens through electronic systems, there are some interesting future 

possibilities that could apply to both heavy trucks and motorcoaches. By integrating ECMs with 

telematics systems, SLs could actually be adjusted “on the fly.” For instance, when a truck 

crosses a State line that moves the speed limit from 105 km/h (65 mi/h) to 113 km/h (70 mi/h), 

the ECM could communicate with a back-office system run by the State and automatically adjust 

the maximum speed to the appropriate State level. In addition, digital maps which have detailed 

speed limit data could be employed to adjust SL settings appropriately as speed limits change.

Such technology may be offered in the future. The comments from EMA and TMA as published 
33 

by Transport Canada (2007) noted that dynamic adjustment of a vehicle speed limit has been 

discussed by industry associations. Their comment was that no standardized method of operation 

has been defined for all vehicles to use, whether based on geo-fencing or satellite 

communications, such that the ability to adjust remotely did not exist at that time.

There is some momentum on the passenger car side that could eventually have some bearing on 

heavy-vehicle SLs. Vision-based systems currently available on luxury cars in Europe have the 

capability to detect and read speed limit signs, displaying this information to the driver. This 

system was first introduced in Europe due to the greater consistency in speed limit signage. 

Conceivably, this type of information could provide the current speed limit to a dynamic SL

system, once techniques are developed for robust speed detection in North America. Before 

vehicle speed can be automatically set by data derived from camera and digital map data, it is 

essential that map-updating techniques and robust video-based image processing algorithms be 

implemented to ensure that the vehicle is truly following the correct speed limit. This would 

include being responsive to dynamic speed limits. 

1.4.6 Summary of the Evaluation of Speed Limiter Implementation in Commercial 

Trucking

SLs are standard equipment on new trucks and motorcoaches and have been for some time (with 

the core technology built into the ECM). Historical problems related to driver tampering have 

been alleviated by the current electronic systems. Because the SL capability is standard, the cost 

to implement SLs is negligible, although some external costs do accrue to fleets in cases where 

external maintenance centers are used to change SL settings.

Fuel conservation and safety were named as the most important benefits of SLs in trucks and 

motorcoaches. Providing drivers with an incentive for improving performance, or rewarding past 

performance, are other benefits offered to carriers through the use of SLs. In terms of the use of 

SLs across the industry, there are a variety of opinions. For trucking, OOIDA contends that 

owner-operators typically do not employ SLs. For company-owned trucks, the surveys 

conducted by OOIDA (2007), ATRI, and the TRB (2008) study indicated that 60 to 63 percent 

use SLs (with variations across sectors). The investigation in the current report yielded much 

higher estimates for fleets, in the range of 75 to 80 percent. Most motorcoaches operate with 

SLs.

With regard to SL settings, the OOIDA (2007) survey found that the preponderance of drivers 

operate in the range of 101–109 km/h (63–68 mi/h), but it is possible that this survey did not 

account for vehicles set above 109 km/h (68 mi/h). EMA and TMA contend that carriers set 

speeds at or below 113 km/h (70 mi/h). The TRB (2008) study found SL settings to fall within 

the 105–111 km/h (65–69 mi/h) range. In the current investigation, SL settings ranged from 100–

113 km/h (62–70 mi/h). Most commercial motorcoach fleets operated with SLs set at 116 km/h 

(72 mi/h); however, many companies have settings below 113 km/h (70 mi/h). 

As to variations in speed settings depending on driver skill or the use of cruise control, the TRB 

(2008) study found that approximately half of the respondents used this practice, with only minor 

differences for cruise control use. However, the investigation in the current study found that none 

of the fleets used programs to allow qualifying drivers to drive at higher speeds. Technology 

trends indicate that vehicles will eventually be “speed limit aware” based on data derived from a 
34 

camera and/or digital map data. However, it is essential that map updating techniques and robust 

video-based image processing algorithms be implemented to ensure that the vehicle is truly 

following the correct speed limit, including dynamic speed limits.
35 

2. METHODS

As stated above, this project aimed to identify SL effects in reducing the severity and frequency 

of crashes, best practices in SL applications, and identification of carrier, insurer, and 

enforcement official views related to SL implementation. To accomplish this goal the following 

tasks were performed: a peer review to obtain feedback on the proposed research design and 

analyses, CMV stakeholders were interviewed, vehicle and crash data were collected directly 

from motor carriers, crash data were reduced to standardize crash types across carriers, and the 

crash data were analyzed to identify the extent to which SLs reduced the frequency of crashes. 

2.1 PEER REVIEW PROCESS

A peer review meeting was conducted to obtain feedback on the proposed methodology to assess

the safety benefits of SLs in CMV operations. Due to the fact that the industry-wide use of speed 

governing devices on commercial trucks and buses involves a diverse group of stakeholders, the 

participants on the panel were selected to include representation from each stakeholder category. 

Below lists the many groups that would be affected by the implementation of SL devices and/or 

who could provide important information related to their potential effectiveness, costs, and 

benefits. The objective of this portion of the effort was not for the participants to indicate their 

support or disapproval of SLs; rather, it was to specifically address the efficiency and 

effectiveness of the data collection and analysis methodology to be used in this study. 

• Truck and bus companies. 

• Truck and bus industry organizations. 

• Driver organizations. 

• Highway safety advocacy organizations.

• Truck and bus manufacturers. 

• Academic researcher organizations.

• Engine manufacturers.

• Federal and State agencies.

2.1.1 Selection of Review Panel Participants

Because the study addressed the safety and operational cost aspects of the implementation of 

SLs, stakeholders from both of these areas are included in the Peer Review Panel. Two forums 

that included these stakeholders were attended by the peer review members: the ATA 

Technology and Maintenance Council Fall Meeting and the ATA Safety Management Council 

Conference. These discussions subsequently helped finalize the list of potential stakeholders that 

were asked to participate on the Peer Review Panel. After approval of the list by FMCSA, the 

potential panel members were contacted by telephone and asked if they were willing to 

participate and available for the Peer Review Panel meeting. A total of 27 participants were 

included in the Peer Review Panel. 
36 

2.1.2 Webinar for Offsite Participants

Prior to the meeting date, the offsite participants were given the Web site address with 

instructions on signing in, along with a password. Figure 5 shows the screen used by the offsite

participants to interact with the panel. The slides of the Research Analysis Plan presentation 

were shown on the screen and the presentation could be downloaded and printed by the 

participants. The Draft Research Analysis Plan could also be downloaded from the site, although 

it had already been sent to all of the participants.

Figure 5. Screen Shot. Webinar Conference Screen Used by Offsite Participants. 

The offsite participants could either type their comments/questions or call them in. If the 

questions/comments were typed into the Web page, both the research team and the other 

participants could read them and respond. The 3-hour peer review meeting was very interactive, 

with extensive discussions among the participants during the presentation of the Research Plan.

At the completion of the presentation, the primary areas related to the data collection and 

analysis methodology that had surfaced were discussed in a more structured format. The primary 

areas of discussion during the peer review meeting are summarized below.

• The operational definition of “speed limiter-relevant crashes.” 

• Alternative data sources. 

• Measures of exposure. 

• Time period to include in the study. 

• Representatives of the fleets used for the study. 
37 

• Driver characteristics. 

• Other safety factors. 

• Operational costs. 

• Sample size (number of fleets and trucks). 

2.1.3 Peer Review Panel Web Site to Obtain Additional Comments and 

Recommendations

Although the formal meeting was very beneficial as a way to present and discuss the Preliminary 

Research Plan, the 3-hour time limit inherently constrained the potential contributions by the 27 

members of the panel. A Web site was developed to allow the Peer Review Panel participants to 

provide additional comments and recommendations after they had a chance to reflect on the 

discussions during the meeting. The Web site allowed the participants to both interactively 

comment on the research design and comment on the issues brought up by the other panel 

members. The content and structure of the Web site was established from the notes taken during 

the Peer Review Panel meeting as well as from the transcript of the meeting. The outline of the 

Web site content that was used to focus the participants’ comments is given below. 

• Research Design.

– Before-and-after comparison of fleets that have recently installed or will install 

speed-limiting devices during the study period.

– Comparison of fleets that set limiters and those that do not.

– Comparison within fleets that have trucks that use limiters and trucks that do not.

– Comparison of fleets that use different SL settings (e.g., 62 mi/h versus 70 mi/h).

– Comparison within fleets that have reduced their SL settings.

– Other alternative or complementary approaches.

• Use of Fleet Safety Data. 

– Fleet safety data content and quality. 

– Measures of exposure.

– Time period for data used in the study.

• Choice of Fleets.

– Types of operations.

– Commodity hauled.

– Method of driver compensation.

• Choice of Roadways. 

• Alternative Sources of Data. 

• Operational Cost Analyses. 

– Fuel costs.
38 

– Maintenance costs.

– Other operational costs.

• Statistical Analysis.

– Analysis of safety data.

– Analysis of operational costs data.

• Other Factors that Impact Accident Rates and Severity.

– Weight of truck.

– Enforcement of speed limit laws.

– Traveling downhill.

– Driver distraction.

– Hours of Service.

In addition to the areas of discussion derived from the Peer Review Panel meeting, the Web site 

also included a list of the names of the research team and the peer review panel membership. 

Another function of the Web site was to allow the Peer Review Panel to comment on the report 

from Phase I (summarized above). The panel members could download the report and make 

comments on the Web page. The Web site outline for the report was as follows.

Literature Review

• Executive Summary. 

• Safety Impacts of Speed. 

• Speed Limiter Regulation. 

• Speed Limiter Technologies and Usage. 

• Safety Results from Implementation. 

• Other Benefits of Speed Limiters. 

• Key Findings. 

• References. 

2.1.3.1 Logistics of the Web site

The Peer Review Panel participants were emailed their individual User Name and Password to 

access the Web site (http://Truckingsafetyresearch.com). Figure 6 shows the home page of the 

Web site.
39 

Figure 6. Screen Shot. Home Page for Peer Review Panel Web Site. 

The panel members could direct their comments by selecting (clicking) the heading at the top of 

the page or the outline to the right. Figure 7 shows an example of a page on which the 

participants input their comments and recommendations. 
40 

Figure 7. Screen Shot. Example of the Interactive Web Site Comments and Reply Area. 

The narrative for each Web site page (e.g., Fleet Safety Data) was developed from the 

combination of the Preliminary Research Plan and the discussion during the Peer Review Panel 

meeting. The panel participants had two weeks to provide comments and recommendations to 

the Web site. The research team reviewed the comments from the Peer Review Panel Web site 

on November 24, 2009. The comments were addressed with respect to the technical and financial 

feasibility, as well as consistency with the scope of the project. Subsequently, a Revised 

Research Analysis Plan was developed. 
41 

FMCSA recommended that the Revised Research Analysis Plan be sent to the panel members 

that represent the academic research community for review and comment. The comments by this 

group indicated that they agreed with the statistical analysis approach of using a logistic 

regression modeling approach. The primary concerns for this group remained the same as those 

previously indicated by the panel as a whole. In particular, there was a concern about the sample 

size (fleets and trucks, within fleet) that is necessary to have sufficient power to detect the impact 

of SL devices. The other comments by the academic group reflected the same concerns as the 

larger group (i.e., that the control or adjustment for the confounding factors is critical to the 

validity of the study). 

2.2 DATA ANALYSIS METHODS

As previously discussed, a number of motor carrier research studies have shown that the use of 

SLs in CMV operations may improve safety (by reducing crash risk and/or crash severity). 

FMCSA has determined that it is important to go beyond these studies and the recently 

completed literature review by Bishop et al. (2008) to provide a better understanding of SL

implementation effects, both from safety (reduction in crash numbers and severity) and 

economic (increased fuel economy) points of view. The data in the current study were collected 

directly from truck fleets and represent a wide array of truck crash types: from minor incidents 

(e.g., scraping an object with a mirror) to fatal crashes. The following research questions were 

assessed in the current study:

• Is there a significant difference in the overall crash rate between the SL and non-SL

cohorts? 

• Is there a significant difference in the SL-relevant crash rate between the SL and non-SL

cohorts? 

• Will different settings on the SL (e.g., 67 mi/h versus 70 mi/h) have a significant impact 

on safety? 

2.2.1 Research Design 

The study design determined the overall structure of the research and guided data collection and 

analyses. The main objective of the current study design was to quantitatively evaluate the safety 

impact and associated fuel benefits of SLs in CMVs. Study designs could be divided into two 

general categories: the experimental study and the observational study (depending on how 

treatment/exposure was determined). The current study was an observational study because of 

the lack of control over the activation and/or installation of an SL in a truck; this decision was 

made at the fleet level. As such, the study followed an epidemiological approach (Rothman, 

Greenland, and Lash, 2008). 

Two study designs, the before-after and the retrospective cohort approaches, were considered. In 

general, the retrospective cohort approach is less prone to time trend bias (e.g., safety 

regulations, etc.), but is subject to the potential confounding effects caused by individual truck 

variations (e.g., safety culture, safety technologies, etc.). The before-after approach has the 

advantage of smaller bias caused by individual truck/fleet variation, but is subject to the 

confounding effects of time trend. The before-after approach is noted here because it was 
42 

indicated as the preferred approach in the statement of work; however, this approach was not 

feasible after reviewing preliminary carrier data (i.e., the study team could not identify fleets that 

had enough data to perform this analysis approach). Given the small frequency of “speed limiterrelevant” crashes (i.e., crashes in which an SL may have prevented the crash and/or reduced 

crash severity) and the inability to control for time (as each carrier activated its speed limiters at 

different times), the retrospective cohort design was selected as the optimal approach. 

2.2.1.1 Retrospective Cohort Approach 

The main objective in the current study was to determine the safety benefits of SLs (i.e., do 

trucks with an active SL have a lower crash risk than those without an active SL?). Since

preliminary data obtained by the research team showed that SL crashes were rare events, there 

were two levels of exposure status in this design: trucks with an active SL (yes), or trucks 

without an active SL (no). More specifically, SLs were considered to improve safety if the trucks 

with an active SL had a lower crash risk than trucks without an active SL. 

Two classical epidemiological methods were considered in the current study: case-control and 

cohort methods. The primary difference between these two methods is the direction of study. In 

the cohort study, the SL status of each truck is determined first (i.e., trucks with an active SL and 

trucks without an active SL). Subsequently, the safety outcomes of each truck are determined. In 

the case-control method, crashes involving a truck with an active SL are identified first. 

Subsequently, a group of trucks without crashes is selected as a control and the status (yes/no) of 

their SL activation is determined. 

The cohort study has several advantages over the case-control study. The cohort study is less 

prone to bias compared to the case-control approach and is considered the gold standard in 

observational studies (such as the current study). Bias is caused by improper control selection; 

however, this approach can be cost-effective for rare safety events (such as crashes). As it was 

possible to collect the SL status in all trucks in the current study, the cohort study is preferred 

(Rothman, Greenland, and Lash, 2008). 

Figure 8 illustrates a schematic plot of the retrospective cohort method used in the current study. 

The study followed a retrospective cohort design approach, based on whether an SL was 

equipped/activated. The trucks were divided into two groups: an SL cohort and a non-SL cohort. 

Note that the two cohorts may not reflect SL carriers versus non-SL carriers, but rather trucks 

with an active SL versus trucks without an active SL within the participating carriers. However, 

the data collected in the current study reflected fleet-wide use or non-use of an SL (i.e., all the 

trucks in a specific carrier had an active SL or vice versa). In each cohort the safety outcome and 

fuel consumption in a specific study period were collected from historical records obtained from 

participating carriers. The safety and fuel benefits of the SL were assessed by comparing the 

outcomes in the two cohorts. 
43 

Figure 8. Diagram. Schematic of the Retrospective Cohort Design to be Used in the Current Study. 

2.2.2 Data Collection Procedures

The two primary analyses noted above were assessed using carrier-collected data. ATRI was 

responsible for collecting all data from the participating carriers. ATRI and the research team

worked collaboratively in collecting the appropriate data. Once data were collected from the 

participating carriers, the data were merged (if necessary), column headings were formatted (to 

uniform headings), a data directory (to identify coding) was created, and a check was made to 

ensure that all the necessary data elements were included (see below for the necessary data 

elements). All trucks in the study were Class 7 or 8 trucks. 

After these data were collected and formatted, ATRI sent these data, via email, to the research 

team. Once received by the research team, the database was reviewed to ensure proper 

formatting. Any issues or discrepancies were resolved through a collaborative process between 

ATRI and the research team. After the research team validated the database sent by ATRI, 

trained personnel reviewed each crash file to determine if the truck crash was an SL-relevant 

crash. 
44 

2.2.2.1 Data Elements

Certain data elements were necessary to ensure all analyses were performed correctly. 

Participating carriers that did not collect the necessary data elements were not included in any 

analyses. Below is a list of requested data elements to assess the two primary analyses (i.e., 

safety and fuel benefits). Note that mileage and fuel information were not available from 

participating carriers. This limited the analyses related to the potential fuel benefits of SLs and 

confounded the safety analysis on SLs (as there was no ability to control for exposure). 

• Crash Information:

– Date.

– State.

– Location (e.g., mile marker on I-81).

– Contributing factor (e.g., excessive speed). 

– Crash type (e.g., rollover). 

– Crash narrative.

– Injury (yes/no).

– Fatality (yes/no).

• Vehicle Information: 

– Vehicle ID number.

– Vehicle year (e.g., 2008). 

– Mileage (for the study period).

– Fuel.

• Carrier Information:

– SafeStat score.

– Fuel efficiency bonus. 

– Fleet type (e.g., for hire: long haul). 

– SL setting (date and SL, if changed).

– Driver pay. 

2.2.2.2 Data Reduction

Although the current study was similar to analyses assessing the effectiveness of onboard safety 

systems (OBSS), studies assessing the safety benefits of OBSSs target specific crash types that 

could have been prevented and/or mitigated with the systems (see Dang, 2004; Houser et al., 

2009; Jermakian, 2010; Murray, Shackelford, and Houser 2009a, b). However, a truck with an 

active SL has many different crash types, and trucks equipped with an active SL will generally 

not have a crash when the truck is traveling above the preset speed (as the truck is prohibited 

from traveling above the preset speed unless the truck is traveling down a grade). Thus, the aim 

of the current study was to identify the types of crashes where an active SL would be most 
45 

effective in mitigating and/or preventing truck crashes; i.e., high-speed (posted speed limit 97 

km/h or 60 mi/h or greater) truck crashes on highways. No trucks in the SL cohort had a setting 

of less than 97 km/h (60 mi/h). 

Trained research personnel who were blind to the SL status of each carrier reviewed several data 

elements included in the crash file to determine if the crash was an SL-relevant crash. An SLrelevant crash was primarily determined by assessing four different variables in the crash file. 

Note that this was necessary as the carrier dataset did not include information on the truck’s 

speed at the time of the crash. 

Note that the following variables were identified during an initial peer review and various 

research team meetings. 

The first variable was the location of the truck crash. The crash must have occurred on a highway 

with a posted speed limit of 97 km/h (60 mi/h) or greater (excluding entrance/exit ramps, truck 

stops, etc.). While several carriers listed the posted speed limit at the time of the crash, others 

carriers did not. In these instances, research personnel used the location information in the crash 

file and cross-referenced that information with the Geographic Information System (GIS) to 

obtain the posted speed limit. Highways with posted speeds limits of 97 km/h (60 mi/h) or 

greater were selected as these are the roads where SLs are most likely to have a potential safety 

benefit. Moreover, highway locations such as truck stops and entrance/exit ramps were excluded 

because it is unlikely an SL would have a benefit in these locations (the truck was likely going 

well below the posted speed limit). 

The second variable was the crash type. Certain crash types were considered indicative of an SLrelevant crash (e.g., rear-end truck striking), while other crash types were clearly not indicative 

of an SL-relevant crash (e.g., truck was turning right). The specific crash types associated and 

not associated with potential SL-relevant crashes are shown below. 

• Crash Types Associated With an SL-Relevant Crash.

– V1 Into rear of V2. 

– V1 Wrong side of road. 

– V2 Wrong side of road. 

– V1 Passing V2. 

– V2 Passing V1. 

– V1 Changed lanes. 

– V2 Changed lanes. 

– V1 Into stationary object. 

– V1 Ran off road. 

– V1 Hit pedestrian.

– V1 Overturn. 

– V1 Jackknife. 
46 

– V2 Hit object in roadway. 

– V1 Out of control. 

– V2 Stopped in roadway. 

– V2 Hit by V1. 

– V1 Hit V2. 

– Sideswipe—Merge. 

– Sideswipe—Opposite. 

– Misc. Unavoidable. 

– Misc. Avoidable. 

• Crash Types Not Associated With an SL-Relevant Crash.

– V1 Hit by unknown vehicle. 

– V1 Left turn squeeze on V2. 

– V2 Left turn squeeze on V1. 

– V1 Right turn squeeze on V2. 

– V2 Right turn squeeze on V2. 

– V1 Lost wheel. 

– V1 Ran stop sign or yield sign. 

– V2 Ran stop sign or yield sign. 

– V1 Left turn. 

– V2 Left turn. 

– V1 Right turn. 

– V2 Right turn. 

– V1 U-Turn. 

– V2 U-Turn. 

– V1 Pulling away from curb. 

– V2 Pulling away from curb. 

– V1 Into parked V2. 

– V2 Into parked V1. 

– V1 Backing. 

– V1 Rollaway. 

– V1 Loading or unloading. 

– V2 Backing. 

– V1 Pulling away from dock. 

– V2 Pulling away from dock. 
47 

– V2 Rollaway. 

– V1 Wreckered, not DOT rec. 

– Unreported accident. 

– Hooking/unhooking. 

– Disputed sign or signal. 

– Open intersection. 

– Dropped TRL or TRK-TRL collision. 

– V2 Into rear of V1. 

– V1 Hit viaduct/underpass. 

– V1 Hit animal. 

– V1 Hit object in roadway. 

– V2 Out of control. 

– Load Shift. 

– Hit by unknown object. 

– Hit by moving object. 

– R/R Crossing. 

The third variable was the contributing factor or factors in the crash. The contributing factor 

variable was used to exclude crashes where speed was clearly not a factor, such as weatherrelated (e.g., ice, rain, etc.), mechanical-related (e.g., brake failure, tire blowout, etc.), and driver 

non-performance errors (e.g., asleep, intoxicated, etc.). Note that animal strikes and objects in the 

roadway were excluded as SL-relevant crashes because most carriers train their drivers to avert 

an avoidance maneuver in these circumstances (the avoidance maneuver would be more 

dangerous than striking the animal and/or object). 

The fourth variable reviewed by research personnel was the crash narrative. This was the most 

important variable to review as the other three variables might suggest an SL-relevant crash; 

however, the crash narrative revealed information that could potentially refute this information. 

For example, a rear-end truck striking crash on a highway with a posted speed limit of 97 km/h 

(60 mi/h) or greater with a contributing factor of following too close might appear to be an SLrelevant crash; however, the crash narrative indicated the crash occurred in bumper-to-bumper 

traffic. See below for a list of keywords that were used to exclude crashes as SL-relevant crashes. 

These keywords were identified during the review of crashes. Crashes were not sorted by these 

keywords to exclude crashes, and a SL-relevant crash could contain one or more of these 

keywords. 

• Keywords Used to Exclude SL-Relevant Crashes.

– Left-hand turn. 

– Right-hand turn. 

– Overpass. 
48 

– Backing. 

– U-turn. 

– Mechanical failure. 

– Hit by other vehicle. 

– Equipment loading damage. 

– Traffic device. 

– Driveway. 

– Curb. 

– Residential area. 

– Fuel Island. 

– Rest area. 

– Hooking. 

– Bridge w/restrictions. 

– Street. 

– Mail box. 

– Tire blow-out. 

– Stop and go traffic. 

– Fuel spilling. 

– Tire flew off other vehicle.

– Intersection. 

– Stop sign. 

– Entrance/Exit ramp. 

– Heavy traffic. 

– Construction zone. 

– Damage to landscape. 

– Dropped trailer. 

– Dock area. 

– Turning. 

– Deer/animal. 

– Fell asleep. 

– Rock or other object thrown at truck. 

– Trailer door open. 

– Pulling-in. 

– Flying debris. 
49 

– Mirrors knocked off. 

– Stopped in traffic. 

– Freight shift. 

– Medical condition. 

– Driving slow. 

– Hit by lightning. 

Note that all variables were reviewed by data analysts in order to determine if the crash was a 

SL-relevant crash. Inconsistencies between variables (contributing factor was noted as “asleep” 

but the crash narrative noted otherwise) were resolved by considering the crash narrative as the 

most accurate. All crash files were reviewed by two different research personnel. Any 

discrepancies between these two research personnel were resolved by a third researcher (interrater reliability was 97.8 percent and intra-rater reliability was 98.4 percent). Once research 

personnel completed their review of each crash, the database was merged into a SAS file for 

analysis. 
50 

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51 

3. RESULTS 

As indicated, the research team completed seven analyses using the datasets provided by ATRI 

and formatted and reduced by the research team. These analyses included: carrier demographics 

and safety management techniques, overall crash rate, SL-relevant crash rate, relationship 

between SL setting and SL-relevant crash rate, and the relationship between fuel consumption 

and SL status and setting. 

3.1 CARRIER DEMOGRAPHICS

The study collected data from 22 carriers in calendar years 2007, 2008, and 2009. Data from two 

fleets were removed because of poor data quality (i.e., unable to determine the location of the 

crash). 

Table 9 displays the demographics for the participating carriers, including: presence of an OBSS, 

Safety Status Measurement System (SafeStat) Safety Evaluation Areas (SEA; driver, vehicle, 

and safety management), sector, mean trip length, commodity types hauled, number of drivers, 

compensation for drivers, and the presence of an active SL. As shown in Table 9, there were six

carriers without an active SL (non-SL cohort) and fourteen carriers with an active SL (SL 

cohort).
52 

Table 9. Carrier Demographic and Safety Management Techniques

ID OBSS Driver 

Safety 

Evaluation 

Area

Vehicle 

Safety 

Evaluation 

Area

Safety 

Management 

Safety 

Evaluation Area

Sector Trip 

Length

Drivers Commodity Types Active 

SL 

1 N/A 18.39 30.62 ISD For-Hire LTL 100–499 >5,000 general freight Yes

2 100% N/A N/A For-Hire LTL 500+ 100–500 general freight, heavy 

machinery, intermodal

Yes

3 No 34.05 34.06 ISD For-Hire TL 500+ 100–500 beverages, building 

materials, chem: liquid 

bulk, general freight, U.S.

mail

No

4 Freightliner 

79% 

International

34%

34.05 34.06 ISD For-Hire TL 100–499 >5,000 beverages, building 

materials, chem: liquid 

bulk, general freight, U.S.

mail

Yes

5 No 12.61 26.75 ISD For-Hire LTL <100 1,001–

5,000

general freight Yes

9 No N/A N/A N/A For-Hire LTL 500+ 501–1,000 general freight Yes

10 No 17.03 45.41 78.4 For-Hire LTL 100-499 >5,000 general freight Yes

11 No 13.25 28.43 ISD For-Hire LTL 100–499 1,001–

5,000

general freight Yes

12 No 12.61 27.39 90.9 For-Hire LTL 100–499 1,001–

5,000

general freight Yes

13 No 31.31 26.88 ISD For-Hire LTL 500+ 501–1,000 general freight, heavy 

machinery, logging, metal

Yes

14 No 22.34 52.78 ISD For-Hire LTL 500+ >5,000 general freight Yes

17 No 37.25 33.87 ISD For-Hire LTL 500+ 501–1,000 general freight, intermodal Yes

18 No 14.49 24.86 ISD For-Hire LTL 100–499 1,001–

5,000

general freight Yes

19 Volvo 100% 40.95 24.2 ISD For-Hire TL 500+ 100–500 farm, general freight, 

refrigerated

Yes

20 85% 67.39 10.43 ISD For-Hire LTL 100–499 <100 refuse, waste Yes
53 

ID OBSS Driver 

Safety 

Evaluation 

Area

Vehicle 

Safety 

Evaluation 

Area

Safety 

Management 

Safety 

Evaluation Area

Sector Trip 

Length

Drivers Commodity Types Active 

SL 

21 N/A 48.79 40.78 ISD For-Hire TL; 

For-Hire 

LTL; OwnerOperator; 

Independent 

Contractor

500+ >5,000 building materials, chem: 

dry bulk, chem: liquid bulk, 

fresh produce, general 

freight, heavy machinery, 

intermodal, logging, metal, 

refrigerated, U.S. mail

No

22 N/A 49.49 45.29 ISD For-Hire TL; 

For-Hire 

LTL; OwnerOperator; 

Independent 

Contractor

500+ 1,001–

5,000

beverages, building 

materials, chem: dry bulk, 

general freight, heavy 

machinery, intermodal, 

logging, metal, 

refrigerated

No

23 N/A 64.43 62.63 ISD For-Hire TL; 

For-Hire 

LTL; OwnerOperator; 

Independent 

Contractor

500+ 1,001–

5,000

building materials, chem: 

liquid bulk, general freight, 

heavy machinery, metal

No

24 N/A 73.46 52.9 ISD For-Hire TL; 

For-Hire 

LTL; OwnerOperator; 

Independent 

Contractor

500+ 100–500 general freight No

25 N/A 23.5 17.64 ISD For-Hire TL; 

For-Hire 

LTL; OwnerOperator; 

Independent 

Contractor

500+ 100–500 beverages, building 

materials, chem: dry bulk, 

fresh produce, general 

freight, heavy machinery, 

metal, refrigerated

No
54 

3.1.1 Carrier Demographic and Safety Management Results

The size of the participating carriers varied from fewer than 100 power units to more than 5,000 

power units. Exact power unit frequencies were not reported to protect the carriers’ anonymity. 

Also, due to existing non-disclosure agreements, the data were scrubbed of any identifying 

carrier information (including USDOT number). As shown in Table 9 above, other demographic 

and safety management characteristics were collected from each carrier. Below is a summary of 

these carrier-specific characteristics. 

• All carriers used a “pay per mile” driver compensation method (including line-haul LTL 

operations). 

• Only a limited number of carriers reported trucks equipped with some type of OBSS. 

Carriers only reported the presence (yes/no) of an OBSS on a truck and did not report the 

specific OBSS. The total number of power units with an OBSS was fewer than 1,000 

power units in any given calendar year. See appendix B for the number of trucks in each 

carrier that had an OBSS. 

• All participating carriers reported being one of three types of trucking operations: for-hire 

LTL, for-hire TL, and a mixture of for-hire TL/ LTL owner-operator/independent 

contractor. As shown in Table 10, five out of six carriers in the non-SL cohort were listed 

as mixture type, whereas the majority of carriers in the SL cohort (11 out of 14) were forhire LTL. 

• The SafeStat SEA scores evaluate the relative safety status of individual motor carriers 

with respect to the rest of the motor carrier population. Higher SEA scores reflect poorer 

performance. Driver SEA scores reflect out-of-service violations, roadside inspections, 

and moving violations, Vehicle SEA scores reflect violations from onsite compliance 

reviews, and Safety Management SEA scores reflect closed enforcement cases and 

compliance reviews. As shown in Table 9 above, all the Safety Management SEA scores 

were recorded as insufficient data (ISD) and two carriers (2 and 9) did not provide any 

SEA scores. The mean SafeStat SEA scores by cohort are shown in Table 11. As can be 

seen in Table 11, the SL cohort had lower Driver and Vehicle SEA scores compared to 

the non-SL cohort. An “analysis of variance” (ANOVA) indicated that the mean Driver 

SEA scores in the SL cohort (26.8) were significantly lower than the non-SL cohort 

(48.96; F(1,16) = 6.73, p = 0.0196). However, the difference in the mean Vehicle SEA 

scores between the SL cohort (30.5) and the non-SL cohort (42.2) was not significant 

(F(1,16) = 3.57, p = 0.077). Carriers did not provide information on specific safety 

management techniques. Note that ANOVA provides a statistical test of whether or not 

the means of several groups are all equal, and therefore generalizes the t-test to more than 

two groups. ANOVAs are helpful as multiple two-sample t-tests would result in an 

increased chance of committing a type I error. For this reason, ANOVAs are useful in 

comparing three or more means (Hayes, 1994). 

• The distribution of mean trip length by cohort is shown in Table 12. 
55 

Table 10. Frequency of Sector by SL Status

Sector SL Cohort Non-SL Cohort

For Hire Less-Than-Truckload 11 0

For-Hire Truckload 3 1

For-Hire TL; For Hire LTL; Owner-Operator; Independent Contractor 0 5

Table 11. SafeStat SEA Scores by SL Status

SEA Score SL Cohort Non-SL Cohort

Mean Vehicle Safety Score 30.5 42.2

Mean Driver Safety Score 26.8 48.9

Table 12. Frequency of Mean Trip Length by SL Status

Mean Trip Length (miles) SL Cohort Non-SL Cohort

<100 1 0

100–499 7 0

≥500 6 6

3.2 DESCRIPTIVE CRASH DATA 

The data from the 20 carriers were collected in calendar years 2007, 2008, and 2009. Some 

carriers did not provide crash records for all 3 years; thus, the dataset was unbalanced. Due to the 

lack of mileage information and the unbalanced years collected by fleet, the research team used 

number of trucks per year (truck-year) as an exposure measure. Table 13 shows the truck-years 

involved in one or more crashes as well as the number of crash-free truck-years over the data 

collection period. 

Table 13. Number of Crashes and Crash-Free Truck-Years by SL Status

Crash Status SL Cohort Non-SL Cohort Total

Truck-Years With Single Crash 13,091 2,076 15,167

Truck-Years With Multiple Crashes 520 2 522

Trucks-Year Without a Crash 111,781 10,605 122,386

Total Truck-Years 125,392 12,683 138,075

3.2.1 Preliminary Crash Rate

The frequency of trucks involved in crashes, crash-free trucks, and crash rate by cohort is listed 

in Table 14. Both overall crash rate and SL-relevant crash rate (see operational definition above) 

were evaluated. As shown in Table 14, the data include 15,866 crash records. Approximately 15 

percent of the crashes were identified as SL-relevant crashes (2,372 out of 15,866). The safety 

impact of SLs was evaluated by the crash rate, which was defined as the ratio of crash frequency 

divided by the number of truck-years multiplied by 100 (as shown in Table 14). Thus, the unit of 
56 

the crash rate was the frequency of crashes per 100 trucks/year (e.g., a crash rate of 10 would 

indicate that 10 crashes would occur for every 100 trucks each year). 

The overall crash rate for trucks without an SL was higher compared to trucks equipped with an 

SL (16.4 versus 11.0 crashes per 100 truck-years). To further evaluate the safety effects of an SL, 

the SL-relevant crash rate was calculated. Similar to the overall crash rate, carriers without an SL

had a much higher rate than carriers with an SL (5.0 versus 1.4 per 100 trucks-years). 

Table 14. Crash Frequency and Crash Rate by SL Status

Frequency SL Cohort Non-SL Cohort Total

SL-Relevant Crashes 1,736 636 2,372

Total Number of Crashes 13,786 2,080 15,866

Total Number of Truck-Years 125,392 12,683 138,075

SL-Relevant Crash Rate* 1.4 5.0 –

Overall Crash Rate* 11.0 16.4 – 

*The unit for crash rate is the number of crashes per 100 trucks/year. 

3.2.1.1 Crash Rate by Carrier and Year 

As noted, crash data from participating carriers were collected in calendar years 2007, 2008, and 

2009. Because many of the carriers provided data for multiple calendar years, it was more 

informative to evaluate the overall and SL-relevant crash rates by carrier and year. The 

frequency of overall crashes, SL-relevant crashes, and the number of crash-free trucks are shown 

in appendix C. Figure 9 and Figure 10 display the overall crash rate and SL-relevant crash rate 

across each carrier in the non-SL cohort and SL cohort. Carriers that reported multiple years of 

data are listed multiple times in the x-axis (e.g., carrier 3 is listed three times as it submitted 3 

calendar years of data). The overall and SL-relevant crash rates varied drastically among carriers. 

More specifically, carriers 5, 18, and 21 had much higher overall crash rates than the other 

carriers. A review of the crash records by data analysts indicated that the criteria for inclusion as 

a crash record were quite different among carriers. Some carriers only included major crashes 

(e.g., significant property or vehicle damage), and other carriers included all types of crashes, 

including minor crashes (e.g., truck drove over bush, truck scraped mirror against a building, 

etc.). However, the SL-relevant crashes identified by the research team had a consistent 

operational definition across fleets. 
57 

Figure 9. Graph. Overall Crash Rate and SL-Relevant Crash Rate by Carrier in the Non-SL Cohort. 

Figure 10. Graph. Overall Crash Rate and SL-Relevant Crash Rate by Carrier in the SL Cohort.

The mean overall crash rate and SL-relevant crash rate across carriers and years in the SL cohort 

(dark red) and non-SL cohort (light red) are shown in Figure 11. It is interesting that the overall 

crash rate and SL-relevant crash rate show a different pattern. However, there was no significant 

0

5

10

15

20

25

30

35

40

45

50

3 3 3 21 22 23 24 25

Crash Rate

Carrier ID

Non-SL Group

Overall Crash Rate

SL-Relevant Crash Rate

0

5

10

15

20

25

30

35

40

45

50

1 1 1 2 2 4 4 4 5 5 5 9 9 9 10 10 10 11 11 11 12 12 12 13 14 14 14 17 17 17 18 18 18 19 19 19 20 20 20

Crash Rate

Carrier ID

SL Group Overall Crash Rate

SL-Relevant Crash Rate
58 

difference in the overall crash rate when comparing the non-SL cohort (9.1 per 100 trucks/year) 

and SL cohort (11.2 per 100 trucks/year; F(1,45) = 0.22, p = 0.645). An ANOVA found that the 

SL-relevant crash rate was significantly higher in the non-SL cohort (2.9 per 100 trucks/year) 

compared to the SL cohort (1.6 per 100 trucks/year; F(1,45) = 6.5, p = 0.014). Note that the mean 

crash rate is the average of crash rates by fleet and year. The raw crash rate was aggregated over 

all fleets; thus it places more weight on large fleets. The research team considered the average of 

fleet-year level crash to be a more robust estimation. In summary, the SL cohort had a 

statistically significant lower SL-relevant crash rate than the non-SL cohort, and the overall crash 

rate between the SL cohort and the non-SL cohort did not differ significantly. 

Figure 11. Chart. Average Overall Crash Rate and SL-Related Crash Rate in the SL and Non-SL 

Cohorts. 

To further quantitatively evaluate the safety effects of SLs, the research team used a negative 

binomial regression model to model the crash count, which is the state-of-practice in modeling

accident frequency (Lord and Mannering, 2010). It is particularly suitable for overdispersion data 

where the Poisson regression model, another commonly used approach, cannot fit the data well. 

The model in Figure 12 is comprised of the following: let Y i j be the number of crashes for 

carrier i in year j. Note that Y i j is assumed to follow a negative binomial distribution, where μ 

(mu) i j is the expected number of crashes for carrier i in year j, and k is an overdispersion 

parameter.

Figure 12. Equation. Negative Binomial Regression Model.
59 

The mean μ (mu) is assumed to be affected by the number of trucks in the carrier and the 

presence of an active SL. The model in Figure 13 is comprised of the following: 

Figure 13. Equation. Log(μij) in the Negative Binomial Regression Model. 

where E i j is the number of trucks in carrier i in year j and X i j is the vector of covariate and beta

is the regression coefficient, alpha i is a random effect associated with carrier i. This model 

incorporated the effects that some carriers contributed multiple calendar years of data. The 

impacts of an active SL can be evaluated by the significance of β (beta). The exponential of beta

is the ratio of crash rate between Non-SL cohort and SL cohort. 

The model outputs are shown in Table 15 and Table 16. Table 15 provides the estimates for 

variance in the carrier-specific random effect and overdispersion parameter and Table 16

provides the estimates for the effects of an active SL. The overdispersion parameter is much 

smaller than one, which indicates the presence of overdispersion and is in support of the negative 

binomial model. Consistent with the simple ANOVA above, the presence of an SL showed a 

significant association with the SL-relevant crash rate (p = 0.0295). The estimated SL-relevant 

crash rate ratio was 1.94 (95 percent Confidence Interval: 1.07–3.49), which indicates that the 

SL-relevant crash rate for carriers in the non-SL cohort was twice that for the carriers in the SL 

cohort. Put another way, the rate for SL-relevant crashes was approximately half of the rate for 

trucks with a SL as compared to trucks without an SL. 

Table 15. The Mixed Effect Model Covariance Parameters Estimates

Covariance Parameter Subject Estimate Standard Error

Intercept Carrier 0.2288 0.1060

Overdispersion Parameter 0.09642 0.03742

Table 16. The Effects of SL Status on the SL-Relevant Crash Rate

Label Regression 

Coefficient 

Estimate

Standard 

Error

P Value SL-Relevant 

Crash Rate 

Ratio

95% 

Confidence 

Interval

Non-SL Versus SL 0.6610 0.2875 0.0295 1.94 1.07–3.49

Confounding effects could potentially be addressed by including the other factors in the model. 

However, the data collected are highly unbalanced, which make this approach not feasible. For 

example the sector variable, the SEA score, and the trip length variable (Table 10 to Table 12) 

are all highly correlated with the SL status. Including these variables could lead to identification

issues and none of the variables was significant. Therefore, the research team adopted the model 

with only the SL status. 
60 

3.2.1.2 Relationship Between SL Setting and SL-Relevant Crash Rate

Figure 14 shows a plot of the relationship between the SL setting (in mi/h) in each carrier and the 

SL-relevant crash rate. The x-axis displays the SL setting and the y-axis displays the SL-relevant

crash rate. Note that some carriers changed their SL setting in a calendar year; so these carriers 

were listed more than once, thus accounting for the extra plotting points. There was no 

meaningful relationship between the SL setting and the SL-relevant crash rate (r = 0.053, p = 

0.75). 

Figure 14. Graph. Plot of SL Setting and SL-Relevant Crash Rate for Carriers in the SL Cohort. 

0

1

2

3

4

5

6

58 60 62 64 66 68 70 72

SL-Relevent Crash Rate

Speed Limiter Setting (mi/h)
61 

4. DISCUSSION 

4.1 CONCLUSIONS FROM ANALYSES OF EFFECTIVENESS OF SPEED 

LIMITERS IN COMMERCIAL MOTOR VEHICLES

The current study assessed the safety benefits of SLs as they operate during normal revenueproducing deliveries. Whereas other studies have assessed the safety benefits of SLs in cars 

(Comte, 1996; Van Loon and Duynstee, 2001; Makinen and Varhelyi, 2001), used simulations 

(Liu and Tate, 2004; Toledo, Albert, and Hakkert, 2007; Transport Canada, 2008b), and assessed 

crash rates in differential posted speed limits (Baum et al., 1991; Harkey and Mera, 1994; 

Johnson and Pawar, 2005), the current study used real-world data collected from carriers. Crash 

data from 20 carriers representing small, medium, and large carriers hauling a variety of 

commodities were used. The data from these carriers included 15,689 crash records and 122,386 

crash-free trucks. In addition, data were collected over a 3-year period (2007–09).The approach 

used in this research went far beyond any previous study in this domain. 

4.1.1 Safety Benefits of Speed Limiters

The primary safety analysis conducted in this study focused on the potential reduction in truck 

crashes that could have been avoided and/or mitigated by installing an active SL. The data used 

in the study was divided into two groups: trucks with an SL and trucks without an SL. The crash 

data were grouped into two groups as well: crashes that were SL-relevant and crashes that were 

not SL-relevant. Analyses included ANOVAs and data modeling (random effect negative 

binomial distribution). The results across analyses indicated a strong, positive safety benefit for 

SLs. 

The ANOVA resulted in two key findings. First, there was no statistically significant difference 

in involvement in the overall crash rate as a function of truck type (SL vs. no-SL, p = 0.65). 

However, for SL-relevant crashes, there was a strong statistically significant difference in crash 

rates showing a clear benefit for trucks with a SL (p = 0.01). This is an important combination of 

findings and serves as a control of unmeasured variables that could possibly have contributed to 

the benefits observed for the SL cohort. As noted in the U.K. study (Transport Canada, 2008a), it 

is possible that contributing factors other than the presence of a SL might have influenced 

observed benefits. For example, it could be (and this was not measured or controlled for) that 

fleets with SL trucks also had in place a positive safety culture. If so, one could make the 

argument the positive effects observed might not have been due to the SL technology, but rather 

due to other safety protocols (i.e., safety culture). However, if this was the case, one would 

expect to see safety benefits in the overall crash rate as well in the SL-relevant crash rate. Why 

would safety culture, for example, only apply to certain crash types (i.e., SL-relevant)? That is, if 

a confounding variable such as safety culture had played a role, then the benefits (i.e., crash rate 

reductions) would be expected in all crash types. In addition, though not significant, the overall 

crash rate was in the opposite direction of what would be expected if a confounding variable, 

such as safety culture, had played a role. As such, the combination of these two results (i.e., a 

non-significant overall crash rate, but highly significant SL-relevant crash rate) supports the 

hypothesis that trucks equipped with SLs in the current study were effective in reducing SLrelevant crashes. 
62 

Moreover, a second confirmatory analysis was conducted whereby a random effect negative 

binomial distribution model was developed to model the crash count. Similar to the ANOVA 

results, a clear benefit was observed with this analysis approach and a significant SL-relevant 

crash rate reduction was found for trucks equipped with SLs (compared to non-SL trucks). The 

results from the modeling analysis were profound in that the resulting calculated SL-relevant 

crash rate ratio (1.94) was approximately twice that for non-SL-equipped trucks compared to 

trucks with an SL. 

4.2 FINAL SUMMARY 

Though much has been learned through this study of SL technology for CMVs, the following 

highlights some key takeaways:

• This study represents the most comprehensive investigation that has ever been conducted 

on SLs. 

• The various analyses conducted used data from more than 138,000 trucks that were 

involved in more than 15,000 crashes.

• Results from multiple analyses indicated a profound safety benefit for trucks equipped 

with an active SL.

• The cost of SL technology is negligible and is a standard feature on new trucks (owners 

only need to activate the device and set the speed limit).

• The positive findings in this study were consistent with the bulk of the literature on this 

topic indicating significant safety benefits associated with speed reduction which can be 

achieved through the implementation of SLs. Domain research on the potential drawback

of speed deviations among vehicles that could occur due to the interaction of SLequipped vehicles and those without SLs seems to be far outweighed by the significant 

safety benefits associated with a reduction in absolute speed afforded by SLs.
63 

APPENDIX A—CONTACTS MADE WITH OTHER 

ORGANIZATIONS 

In conducting this literature review in Phase I, the study team contacted government agencies 

outside the U.S., seeking further information on SL studies, both published and unpublished. 

These agencies were queried as to past and current applications, programs, and studies involving 

the use of SLs; further, these contacts were asked to provide guidance on any other SL safety 

effectiveness studies. 

• VicRoads, Vehicle Safety Department, Australia

Angus Draheim, Assistant Director (Vehicles and Road Use), Land Transport and Safety 

Division, Queensland Transport and Main Roads, Australia 

• Robert de Maid, Senior Policy Analyst—Safety and Environment, National Transport 

Commission, Australia

• Pierre Thiffault, Transport Canada 

• Doug Switzer, Vice President Public Affairs, Canadian Trucking Alliance, Ontario 

Trucking Association 

• Jean-Paul Repussard, Directorate General Energy and Transport, Unit E3—Road Safety, 

European Commission 

• Anders Godal Holt, ITS and Traffictechnology, Norwegian Public Roads Administration, 

Vegvesen, Norway

• Mats Hjälm, Senior Administrative Officer, Road Traffic Department, Swedish Road 

Administration

• Hans Eriksson, Senior Advisor, Commercial traffic department, Swedish Transport 

Agency 

• Ulf Hammerstrom, Mohammed-Reza Yahya, VTI (Swedish National Road and Transport 

Research Institute)

• Marianne Vanderschuren, Dept. of Civil Engineering, University of Capetown, South 

Africa 

• Robert Haggar, Roadworthiness Team, Department for Transport, U.K.

• Clive Taylor, VOSA Speed Limiter Policy and U.K. Digital Tachograph Risk Manager, 

Vehicle and Operator Services Agency, Department for Transport, U.K..
64 

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65 

APPENDIX B—FREQUENCY OF TRUCKS WITH AN 

ONBOARD SAFETY SYSTEM BY YEAR

Table 17. Frequency of Trucks With an Onboard Safety System by Year

Carrier Without 

OBSS 2007

Without 

OBSS 2008

Without 

OBSS 2009

With OBSS 

2007

With OBSS 

2008

With OBSS 

2009

1 4,197 4,197 4,197 0 0 0

2 0 1 NA 84 84 NA

3 652 648 646 0 0 0 

4 6,640 6,483 6,256 0 0 0 

5 3,929 4,049 3,968 0 0 0

9 603 582 607 0 0 1

10 4,220 4,165 4,082 0 0 0 

11 812 794 782 0 3 0

12 1,621 1,554 1,521 0 0 0

13 NA NA 423 NA NA 0

14 16,470 16,294 15,849 0 2 6 

17 881 892 872 0 0 0 

18 2,337 2,238 2,153 0 0 0

19 179 172 178 128 128 128

20 12 12 11 64 67 68

21 NA 6,024 NA NA 0 NA

22 NA 2,912 NA NA 0 NA

23 NA 1,194 NA NA 0 NA

24 NA 171 NA NA 0 NA

25 NA 438 NA NA 0 NA

Total 42,553 52,820 41,545 276 284 203
66 

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67 

APPENDIX C—CRASH FREQUENCY BY YEAR AND 

CARRIER 

Table 18. Crash Frequency by Year and Carrier

SL Status Carrier 

ID

Year Total Crash

Frequency

SL-Relevant 

Crash 

Frequency

Number 

of 

Trucks

Overall 

Crash 

Rate*

SL-Relevant 

Crash Rate*

Non-SL Cohort 3 2007 24 7 652 3.7 1.1

Non-SL Cohort 3 2008 20 5 647 3.1 0.8

Non-SL Cohort 3 2009 18 4 645 2.8 0.6

Non-SL Cohort 21 2008 1,631 486 6,024 27.1 8.1

Non-SL Cohort 22 2008 241 70 2,912 8.3 2.4

Non-SL Cohort 23 2008 82 41 1,194 6.9 3.4

Non-SL Cohort 24 2008 17 4 171 9.9 2.3

Non-SL Cohort 25 2008 47 19 438 10.7 4.3

SL Cohort 1 2007 228 64 4,425 5.2 1.4

SL Cohort 1 2008 189 63 4,386 4.3 1.4

SL Cohort 1 2009 154 30 4,351 3.5 0.7

SL Cohort 2 2007 3 0 84 3.6 0.0

SL Cohort 2 2008 4 2 85 4.7 2.4

SL Cohort 4 2007 875 213 6,601 13.3 3.2

SL Cohort 4 2008 718 171 6,462 11.1 2.6

SL Cohort 4 2009 491 96 6,246 7.9 1.5

SL Cohort 5 2007 1,544 44 3,929 39.3 1.1

SL Cohort 5 2008 1,664 46 4,049 41.1 1.1

SL Cohort 5 2009 1,583 62 3,968 39.9 1.6

SL Cohort 9 2007 55 16 601 9.2 2.7

SL Cohort 9 2008 34 9 582 5.8 1.5

SL Cohort 9 2009 60 29 605 9.9 4.8

SL Cohort 10 2007 264 75 4,215 6.3 1.8

SL Cohort 10 2008 209 91 4,161 5.0 2.2

SL Cohort 10 2009 126 40 4079 3.1 1.0

SL Cohort 11 2007 69 8 809 8.5 1.0

SL Cohort 11 2008 54 7 794 6.8 0.9

SL Cohort 11 2009 39 9 781 5.0 1.2

SL Cohort 12 2007 148 26 1,614 9.2 1.6

SL Cohort 12 2008 81 14 1,553 5.2 0.9

SL Cohort 12 2009 48 7 1,521 3.2 0.5

SL Cohort 13 2009 20 11 422 4.7 2.6

SL Cohort 14 2007 1,023 193 16,430 6.2 1.2

SL Cohort 14 2008 849 168 16,281 5.2 1.0

SL Cohort 14 2009 408 72 15,848 2.6 0.5

SL Cohort 17 2007 35 7 878 4.0 0.8

SL Cohort 17 2008 46 13 891 5.2 1.5

SL Cohort 17 2009 26 6 871 3.0 0.7

SL Cohort 18 2007 978 40 2,337 41.8 1.7

SL Cohort 18 2008 879 38 2,238 39.3 1.7
68 

SL Status Carrier 

ID

Year Total Crash

Frequency

SL-Relevant 

Crash 

Frequency

Number 

of 

Trucks

Overall 

Crash 

Rate*

SL-Relevant 

Crash Rate*

SL Cohort 18 2009 794 40 2,153 36.9 1.9

SL Cohort 19 2007 29 9 306 9.5 2.9

SL Cohort 19 2008 22 7 298 7.4 2.3

SL Cohort 19 2009 28 8 304 9.2 2.6

SL Cohort 20 2007 1 0 76 1.3 0.0

SL Cohort 20 2008 4 0 79 5.1 0.0

SL Cohort 20 2009 4 2 79 5.1 2.5
69 

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