OFFICE OF MOTOR CARRIER SAFETY

Contact: Anthony Schafer, HMPC-10, (202) 366-2953

The Unsafe Driving Acts of Motorists

in the Vicinity of Large Trucks

Introduction

The fatal crash rate of large trucks has declined significantly over the past decade,

from more than 4 per million miles driven during the 1980s, to approximately 2.5 per

million miles traveled now. In 1996, large trucks composed 8 percent of all vehicles

involved in fatal crashes; however, truck-involved crashes resulted in 12 percent of the

total fatalities. Occupants of large trucks compose only 14 percent of the fatalities

resulting from fatal truck crashes; 86 percent of the fatalities occur outside the truck,

to pedestrians, cyclists, and primarily, the occupants of passenger vehicles. The greater

mass of large trucks better absorbs the energy generated in a collision, leaving a 

smaller vehicle at a disadvantage.

By identifying driving behaviors that lead to collisions between passenger vehicles and

large trucks, countermeasures can be developed to further reduce the incidence and

severity of crashes. This tech brief summarizes a study concerning unsafe driving acts

(UDAs) of motorists in the vicinity of large trucks. UDAs are defined as motorist 

behaviors that contribute to collisions. The study final report will be available from the

National Technical Information Service. 

Purpose

The purpose of this initiative was to identify UDAs of motorists in the vicinity of large

trucks as contributing factors in fatal truck crashes, in order to target these behaviors

and develop countermeasures. Additional objectives included the development of 

recommendations for training materials and possible changes to the Uniform Vehicle

Code and Model Traffic Ordinance (UVCMTO). 

Methodology

The project comprised several research tasks, including: 1) review and analysis of 

statistical crash data; 2) interviews with truck drivers, collision investigators, and other

experts; 3) review and analysis of collision investigation reports; and 4) a systematic 

rating of the UDAs by a sample of experts.

Researchers reviewed statistical summaries of crash data to identify the types of trucks

and roadways that are most involved in fatal collisions. The primary source of data

used during this project task was the U.S. Department of Transportation’s Fatality

Analysis Reporting System (FARS). FARS data were obtained for the year 1995, the most

recent complete year at the time of the analysis. Collision investigation reports from

seven States were also reviewed, and researchers tabulated the primary collision factors

for collisions in which the driver of a passenger vehicle contributed to the crash.

Open-ended interviews with subject matter experts were conducted to identify the

UDAs of motorists that lead to collisions with large trucks. The participating experts

included truck drivers, collision investigators, and Federal and State officials. A panel 

Tech Brief

The mission of the Office of

Motor Carrier Safety is to

develop and promote, in 

coordination with other

Departmental modes, 

data-driven, analysis-based,

and innovative programs to

achieve continuous safety

improvements in the Nation’s

highway system, intermodal

connections, and motor carrier

operations. The Office of

Motor Carrier Research and

Standards manages the 

safety regulatory program 

and the central research 

management function for

Motor Carrier Safety.

There are eight major research

and technology focus areas:

regulatory evaluation and

reform; compliance and

enforcement; driver training

and performance management; driver alertness and

fatigue; driver physical 

qualifications; car-truck 

proximity; HAZMAT safety 

and cargo tank integrity; and

crash causation and profiling.

Car-truck proximity involves

studies of the interaction of

trucks with proximal “other

road users” such as cars, light

trucks, and vans.

Office of Motor Carrier Research

and Standards

400 Seventh Street, SW

HMCS-30; Room 3107

Washington, DC 20590
of experts then ranked the identified UDAs in order

of frequency and danger.

A rating instrument/form was developed to permit

experts to assign values to each UDA with respect to

how dangerous a behavior is, and how frequently it

occurs. Each UDA was presented along with two 

10-point scales. The first scale asked respondents to

estimate the danger of the act, defined as a combination of the probability and severity of a collision

when committed by a motorist in the vicinity of a

large truck. The second scale asked respondents to

estimate the frequency with which the driving act

occurs. Rating forms were sent to 25 subject matter

experts and were returned by 21. 

Findings

The lists of unsafe driving acts resulting from the 

statistical reviews, interviews with experts, and 

review of collision investigation reports were used to

develop a final list of UDAs, including:

• Changing lanes abruptly in front of a truck

• Driving left of center

• Following too closely

• Unsafe passing, primarily with insufficient headway

• Unsafe speed

• Merging improperly

• Driving between large trucks

The experts reported that the condition most 

common in collisions involving passenger vehicles and

large trucks is motorists’ unfamiliarity with the 

performance limitations and capabilities of large

trucks. It appeared that most drivers are unaware of

the limited acceleration, braking, and visibility of

large trucks and of the relationship between mass

and velocity and the potential consequences of that

relationship to safety. Particularly distressing to truck

drivers is when a motorist passes a large truck, quickly

cuts in front of it, then exits the highway.

Table 1 presents the first 10 UDAs listed in descending

order of danger, and Table 2 presents the first 10

UDAs in order of their frequency, as determined by

the experts’ rating. Standard deviations from the

mean were calculated for all UDAs. This procedure

found considerable agreement among experts 

concerning the relative danger of the UDAs, but

greater variance in their ratings of frequency.

In order to reflect both the relative danger and 

relative frequency of each UDA, researchers combined

the mean scores for the two categories in a separate

metric, labeled criticality. Criticality values placed

equal weight on the expert’s ratings of danger and

frequency; the first 10 UDAs in descending order of

criticality are presented in Table 3. 

Using the criticality metric, driving behaviors that

were considered extremely dangerous, but infrequent, could reasonably be compared to UDAs that

are only moderately dangerous, but happen more 

frequently. For example, experts rated “Following too

closely”as the most frequent of the UDAs, but placed

it 17th in terms of danger; the composite ranking

places it sixth on the criticality list. Experts rated

“Driving inattentively” as the seventh most dangerous UDA and the third most frequent, placing it at

the top of the criticality list.

Table 1. 

Unsafe Driving Acts: Experts’ Rating of Danger

Mean Score: Unsafe Driving Act

Danger

9.67 Driving left of center or into opposing traffic

9.62 Unsafe passing, primarily passing with insufficient headway

9.52 Driving while impaired by alcohol or other drug

9.14 Failure to stop for a stop sign or light (also, early or late through a signal)

8.95 Failure to discern that the trailer of a maneuvering truck is blocking the roadway

8.90 Unsafe crossing, primarily crossing traffic with insufficient headway

8.76 Driving inattentively (e.g., reading, talking on phone, fatigue-induced inattention)

8.76 Merging improperly into traffic, causing a truck to maneuver or brake quickly

8.76 Pulling into traffic from roadside in front of a truck without accelerating sufficiently

8.71 Unsafe turning, primarily turning with insufficient headway
Conclusions/Recommendations

By reviewing relevant statistical summaries, interviewing a representative sample of subject matter experts,

recording contributing factors from a large sample 

of collision investigation reports, and conducting a

systematic rating procedure, researchers compiled an

ordered list of the UDAs of motorists in the vicinity of

large trucks. Unfamiliarity with performance limitations of large trucks appeared to be a contributing

factor to many of the unsafe acts of motorists.

Researchers recommended that the results of the

study be applied to the development of training

materials for truck drivers, drivers of passenger 

vehicles, and law enforcement officers. In developing

training materials for truck drivers, the list of UDAs in

table 3 could serve as a checklist of the motorist

behaviors of which truck drivers must remain aware

while on the road. To remedy motorist unfamiliarity

with the performance limitations of large trucks,

researchers suggest that public information and 

education programs be developed to illustrate the

Table 2. 

Unsafe Driving Acts: Experts’ Rating of Frequency

Mean Score: Unsafe Driving Act

Frequency

8.05 Following too closely

8.00 Unsafe Speed (e.g., approaching too fast from the rear, misjudging truck speed)

7.90 Driving inattentively (e.g., reading, talking on phone, fatigue-induced inattention)

7.76 Driving in the “No-Zones” (left rear quarter, right front quarter, and directly behind)

7.67 Merging improperly into traffic, causing a truck to maneuver or brake quickly

7.62 Failure to slow down in a construction zone

7.48 Failure to slow down in response to environmental conditions (e.g., fog, smoke, rain,

bright sun)

7.10 Failure to stop for a stop sign (also, early or late through a signal)

7.10 Changing lanes abruptly in front of a truck

6.71 Changing lanes in front of a truck, then braking (for traffic, obstacle, toll gate, etc.)

Table 3. 

Unsafe Driving Acts: Experts’ Rating of Criticality (Danger + Frequency)

Combined Unsafe Driving Act

Mean Scores

16.67 Driving inattentively (e.g., reading, talking on phone, fatigue-induced inattention)

16.43 Merging improperly into traffic, causing a truck to maneuver or brake quickly

16.24 Failure to stop for a stop sign or light (also, early or late through a signal)

16.19 Failure to slow down in a construction zone

16.05 Unsafe speed (e.g., approaching too fast from the rear, misjudging truck speed)

15.95 Following too closely

15.86 Failure to slow down in response to environmental conditions (e.g., fog, smoke, rain,

bright sun)

15.67 Changing lanes abruptly in front of a truck

15.43 Driving in the “No-Zones” (left rear quarter, right front quarter, and directly behind)

15.29 Unsafe passing, primarily passing with insufficient headway
Researcher

This study was performed by

Anacapa Sciences, Inc., Santa

Barbara, CA 93102. Contract

No. DTFH61-97-C-00090.

Distribution

This Tech Brief is being distributed according to a standard

distribution. Direct distribution

is being made to the Resource

Centers and Divisions.

Availability

The study final report will be

available from the National

Technical Information Service,

Telephone: (703) 605-6000.

Key Words

trucks, unsafe driving, law

enforcement, collisions, 

highway safety, commercial

motor vehicles.

Notice

This Tech Brief is disseminated

under the sponsorship of the

Department of Transportation

in the interest of information

exchange. The Tech Brief 

provides a synopsis of the

study’s final publication. The

Tech Brief does not establish

policies or regulations, nor 

does it imply USDOT endorsement of the conclusions or 

recommendations. The U.S.

Government assumes no 

liability for its contents or 

their use.

acceleration, braking, and turning limitations of trucks. It was also recommended that

training materials for law enforcement officers help distinguish between driving acts

that are code violations, such as “Following too closely,” and those that are unsafe but

not illegal, such as “Driving in the No-Zones.” Training materials should also help 

sensitize officers to the dangers associated with UDAs.

Another objective of the current study was to explore the possibility of implementing

changes to vehicle codes that would permit officers to cite drivers for unsafe driving

practices that currently are not vehicle code violations. The recommended method for

encouraging changes to vehicle codes is to propose that the changes be made to the

Uniform Vehicle Code and Model Traffic Ordinance (UVCMTO). 

The UVCMTO was written to provide States with a model to use in developing traffic

citations; however, it does not specifically address the issue of UDAs of passenger 

vehicles in the vicinity of trucks. Researchers suggested that special consideration or

penalties are warranted when UDAs are committed in the vicinity of large trucks,

because of the greater possibility of serious injury or fatalities resulting from collisions

between passenger vehicles and large trucks, compared to collisions between 

passenger vehicles. 

November 1999

Publication No. MCRT-00-002