FEDERAL HIGHWAY ADMINISTRATION • OFFICE OF MOTOR CARRIER AND HIGHWAY SAFETY

FHWA Contact: Ralph Craft, HMIA-20, (202) 366-0324

Longer Combination Vehicles Involved

in Fatal Crashes, 1991–1996

Introduction

States exercise primary responsibility for setting truck length and weight limits within their

borders, as long as they are consistent with Federal regulations. For crash purposes, therefore, there is no nationally uniform definition of a longer combination vehicle (LCV).

The Surface Transportation Assistance Act of 1982 (STAA) required States to permit tractors

to pull two trailers, each up to 28.5 feet long, on Interstate highways and on other routes

recommended by the States and designated by the Federal Highway Administration. In some

States, no doubles were allowed before the STAA. 

The Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 defined an LCV as “any

combination of a truck tractor and two or more trailers or semi-trailers which operates on

the Interstate System at a gross vehicle weight greater than 80,000 pounds.” The legislation

also provided that no State could permit multi-trailer trucks longer or heavier than those

operating on National Network (NN) routes under existing State laws as on June 1, 1991,

thus “freezing” State weight and length limits for these trucks. Since different State laws

allowed various size and weight limits on NN highways, State highways, and local roads

before 1991, ISTEA froze the existing variation among the States on the Interstate system

and other NN routes.

To account for the variation in State definitions and federal statutes, the following 

definition of an LCV used in this report combines elements from the STAA and ISTEA. An

LCV is a truck that meets one or more of the following criteria:

• a truck-tractor with at least two trailers, at least one of which is 29 feet long or longer;

• a truck-tractor with at least two trailers and a gross combination weight (GCW) greater

than 80,000 pounds; or

• a truck-tractor with three trailers.

Overlength LCVs have at least one cargo-carrying trailer longer than 28.5 feet. Overweight

LCVs exceed the weight standard only (i.e., both trailers are within the length standard but

the GCW of the vehicle exceeds 80,000 pounds). LCVs categorized as both exceed both the

weight and length standards. Triples are LCVs with three trailers. The term “LCV” in this

report includes all LCVs: overlength, overweight, both, and triples. In this report a trucktractor, two-trailer combination that falls within the length limits established by the STAA 

of 1982 and the weight limits of the ISTEA or 1991 is classified as an STAA double. Figure 1

provides examples of some LCVs and common non LCVs.

This analysis brief is based on data from the University of Michigan’s Trucks Involved in Fatal

Accidents (TIFA) file. No comparable data are available for nonfatal crashes. Since only a relatively small number of LCVs are involved in fatal crashes in any given year, 6 years of data,

1991 through 1996, were combined in order to produce a more meaningful sample.

Distributions for STAA doubles and other non-LCV tractor-semitrailers are also presented for

comparison and perspective. 

Crash Involvement Trends, 1991–1996

Table 1 presents the number of fatal involvements for LCVs broken down by whether they

are classified as LCVs by their length, weight, both length and weight, or as triple trailers.

The table presents data on the number of LCVs involved in fatal crashes for each year from

1991 through 1996, and for comparison also provides the number of STAA doubles and 

tractor-semitrailers involved in fatal crashes.

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other Departmental modes,

data-driven, analysis-based,

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highway safety infrastructure

program development and

evaluation.

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motor carrier and highway

safety crash trends, monitors

patterns in motor carrier

inspection rates, evaluates

program effectiveness in

reducing crashes, and

researches crash causation 

and exposure data. It also conducts cost/benefit analyses

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analyses to address new or

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Analysis Brief
The number of LCVs involved in fatal crashes has fluctuated between 24 and 50 per year over the last 6 years,

with an average of about 37 per year (Table 1). An 

average of 132 STAA doubles and 2,865 non-LCV tractorsemitrailers per year were involved in fatal crashes from

1991 through 1996. Thus, in an average year, LCVs 

constituted only a very small number — slightly more

than 1 percent — of the combination trucks involved in

fatal crashes.

Note that STAA double combinations that qualified as

LCVs solely because their gross combination weight was

over 80,000 pounds at the time of the crash would not

be LCVs when empty or with lesser amounts of cargo.

STAA doubles classified as LCVs solely by weight 

constitute a quarter of all LCVs involved in fatal crashes

over the 6-year period. 

Geographic Distribution of LCV Fatal Crash

Involvements

Longer combination vehicles are permitted in 26 States.

Every State west of the Mississippi River except for

California, Texas, Arkansas, Louisiana, and Minnesota

allow LCVs on at least some highways. The western

States historically have permitted longer truck combinations, in part because of the great distances and low

population densities between urban centers. 

Only six States east of the Mississippi permit LCVs:

Indiana, Ohio, Michigan, New York, Massachusetts, and

Florida. LCVs are restricted to toll roads in all Eastern

States except Michigan, which allows LCVs on many

major highways. Michigan permits two-trailer combinations to weigh up to 164,000 pounds with the appropriate number and spacing of axles — the highest allowable weight of all States. The operations of triples are

tightly restricted to certain roads in 15 sparsely populated Western States, plus the Indiana and Ohio turnpikes.

There were 33 LCVs involved in fatal crashes in Michigan

during 1991-1996; this was 15 percent of the national

total. Only eight other States averaged more than one

LCV involvement in a fatal crash per year, and all are in

the far West. In Washington State, there were 29 LCVs

involved in fatal crashes during the 6-year period, in

Oregon there were 20, and in California there were 22;

these three west coast States together accounted for

almost one-third of all crashes. The other States that

Figure 1. 

Longer Combination Vehicles and some

Common Non-LCVs.

Table 1. 

Combination Trucks Involved in Fatal Crashes, 1991–1996.

LCVs 1991 1992 1993 1994 1995 1996 Total Percent

Overlength 15 16 13 10 19 14 87 39%

Overweight 2 12 6 17 10 9 56 25%

Both 7 14 9 13 20 5 68 31%

Triple Trailers 0 3 1 2 1 3 10 5%

LCV Total 24 45 29 42 50 31 221 100%

STAA Doubles 135 132 139 116 122 145 789

Tractor-Semitrailers 2,659 2,478 2,635 2,799 2,667 2,943 16,181

Source: Trucks Involved in Fatal Accidents (TIFA), 1991–1996

Table 2. 

Combination Trucks Involved in Fatal

Crashes by Length, 1991–1996.

Length LCVs STAA Tractorin Feet Doubles Semitrailers

30-59 1 (0%) 19 (2%) 6,299 (39%)

60-69 30 (14%) 217 (28%) 8,842 (55%)

70-79 65 (29%) 532 (67%) 634 (4%)

80-89 59 (27%) 21 (3%) 17 (0%)

over 89 65 (30%) 0 (0%) 7 (0%)

Unknown 1 (0%) 0 (0%) 382 (2%)

Totals 221 (100%) 789 (100%) 16,181 (100%)

Source: TIFA, 1991–1996

TractorSemitrailer

STAA DoubleTrailer

Rocky Mountain

Double

Turnpike 

Double

Triple-Trailer

Combination
averaged more than one LCV involvement in a fatal

crash per year were Montana and Utah with 18 each

over the 1991-1996 period, Idaho and Nevada with 13

and Wyoming with 8. 

Physical characteristics of LCVs involved in

fatal crashes

Each of the three major types of combination trucks has

a distinctive length profile (Table 2). Almost three-fifths

(57 percent) of LCVs involved in fatal crashes exceeded

79 feet in overall length, with 30 percent exceeding 89

feet in length. Most of the rest (29 percent) were

between 70 and 79 feet long. In contrast, two-thirds (67

percent) of STAA doubles fell between 70 and 79 feet in

length, with only 3 percent exceeding 79 feet. Almost all

(94 percent) of the tractor-semitrailers involved in fatal

crashes were shorter than 70 feet. Almost two-fifths (39

percent) were less than 60 feet long, while none of the

LCVs and only 2 percent of the STAA doubles were less

than 60 feet in length.

LCVs involved in fatal crashes have a weight distribution

very different from STAA doubles and tractor-semitrailers

(Table 3). Three-fifths (60 percent) of LCVs involved in

1991-1996 fatal crashes had gross combination weights

of more than 80,000 pounds among those vehicles for

which a weight could be determined. Close to one-fifth

(16 percent) had a GCW exceeding 120,000 pounds. 

The heaviest vehicle weighed 225,000 pounds and was

carrying a bridge beam. 

None of the STAA doubles and only 3 percent of the

tractor-semitrailers weighed over 80,000 pounds. Almost

half (48 percent) of the STAA Doubles and 40 percent of

the tractor-semitrailers fell into the 60,001 to 80,000

pound range, as opposed to only 7 percent of LCVs. At

the low end of the scale, 18 percent of LCVs, 24 percent

of STAA doubles, and 35 percent of tractor-semitrailers

had gross combination weights of 40,000 pounds or less.

LCVs involved in fatal crashes show a wider variety of

cargo body types than STAA doubles or tractorsemitrailers (Table 4). Almost two-thirds (64 percent) of

the STAA doubles and over half (54 percent) of tractorsemitrailers had van type cargo compartments. By 

contrast only 25 percent of LCV cargo bodies were vans.

Another 30 percent of LCVs involved in fatal crashes

were dump cargo bodies, 25 percent were flatbeds, and

16 percent were tank type cargo bodies. Flatbeds

accounted for 18 percent of STAA double involvements

and 19 percent of tractor-trailer involvements. The other

cargo body types for these combinations accounted for

considerably less of the fatal involvements.

Tractor-semitrailers are the primary workhorse in the

general truck transportation industry, and STAA doubles

are commonly used for long-haul transport of general

freight. Thus, both employ mostly vans to carry their

cargo. Flatbeds are able to accommodate extra long

loads, such as bridge or building beams, that would not

fit in an enclosed van. Dump truck cargo bodies can carry

very heavy loads, such as gravel, that do not need to be

carried in an enclosed container. For these reasons

flatbeds and dump cargo bodies are more common

among LCVs. 

Carriers and trip types of LCVs involved in

fatal crashes

Just over three-fourths (76 percent) of LCVs and just

under three-fourths (74 percent) of STAA doubles

Table 4. 

Combination Trucks Involved in Fatal

Crashes by Cargo Body Type, 1991–1996.

Cargo LCVs STAA TractorBody Type Doubles Semitrailers

Van 56 (25%) 504 (64%) 8,732 (54%)

Flatbed 56 (25%) 140 (18%) 3,030 (19%)

Tank 36 (16%) 36 (4%) 1,625 (10%)

Dump 67 (31%) 93 (12%) 1,766 (11%)

Other/ 6 (3%) 16 (2%) 1,028 (6%)

Unknown

Total 221 (100%) 789 (100%) 16,181 (100%)

Source: TIFA, 1991–1996

Table 5. 

Combination Trucks Involved in Fatal

Crashes by Trip Type, 1991–1996.

Trip Type LCVs STAA TractorDoubles Semitrailers

Local 63 (27%) 153 (19%) 3,706 (23%)

51–200 miles 114 (53%) 421 (54%) 4,159 (26%)

Over 200 39 (18%) 189 (24%) 6,919 (43%)

miles

Unknown 5 (2%) 26 (3%) 1,397 (8%)

Total 221 (100%) 789 (100%) 16,181 (100%)

Source: TIFA, 1991–1996

Table 3. 

Combination Truck Involved in Fatal Crashes

by Gross Combination Weight, 1991–1996.

Gross LCVs STAA TractorCombination Doubles Semitrailers

Weightpounds

up to 40,000 40 (18%) 189 (24%) 5,583 (35%)

40,001–60,000 18 (8%) 192 (24%) 2,250 (14%)

60,001–80,000 15 (7%) 377 (48%) 6,538 (40%)

80,001–100,000 47 (22%) 0 (0%) 428 (3%)

100,001– 49 (22%) 0 (0%) 59 (0%)

120,000

over 120,000 36 (16%) 0 (0%) 15 (0%)

Unknown 16 (7%) 31 (4%) 1,308 (8%)

Totals 221 (100%) 789 (100%) 16,181 (100%)

Source: TIFA, 1991–1996
Researcher

This study was performed 

jointly by the Center for

National Truck Statistics,

University of Michigan

Transportation Research Center

and the Office of Data Analysis

and Information Systems,

OMCHS, Federal Highway

Administration. Contract No.

DTFH61-96-C-0038.

Distribution

This Analysis Brief is being 

distributed according to a 

standard distribution. Direct

distribution is being made to

the Resource Centers and

Divisions.

Availability

This Analysis Brief is available

from the Office of Data

Analysis and Information

Systems, Telephone: (202) 

366-1861.

Key Words

longer combination vehicle,

triple, STAA double, tractor

semi-trailer, overlength, 

overweight.

Notice

This Analysis Brief is disseminated under the sponsorship 

of the Department of Transportation in the interest of

information exchange. The

Analysis Brief provides a 

synopsis of the study’s final

publication. The Analysis Brief

does not establish policies or

regulations, nor does it imply

FHWA endorsement of the 

conclusions or recommendations. The U.S. Government

assumes no liability for its 

contents or their use.

involved in fatal crashes in 1991-1996 were operated by carriers in interstate commerce. An

even greater number (83 percent) of tractor-semitrailers were operated by interstate carriers. The fact that about one-quarter of STAA doubles and LCVs were operated by intrastate

carriers likely reflects individual State regulations limiting the number and type of roads on

which STAA doubles and LCVs can operate, and whether LCVs can operate on any roads in a

State. 

LCVs involved in fatal crashes were more likely to have been dispatched on short trips than

STAA doubles and tractor-semitrailers. Only 19 percent of STAA doubles and 23 percent of

tractor-semitrailers were on trips of less than 50 miles when they were involved in a fatal

crash, while 29 percent of LCVs were on local trips (Table 5). Moreover, half of the LCVs and

STAA doubles were on trips between 51 and 200 miles, compared to only 26 percent of the

tractor-semitrailers. At the long trip end of the scale, only 18 percent of LCVs were on trips

of more than 200 miles in length, while the number for STAA doubles was 24 percent and

for tractor-semitrailers the number climbs to 43 percent. 

The concentration of LCVs on short trips reflects cargo that is extra long or extra heavy and

does not have to be moved great distances. On the other hand, much tractor-semitrailer

traffic is cross-country in nature. The short LCV trips are also a product of restrictions that

prevent LCVs from entering surrounding States or using many roads in their home States.

Fatal crash events

For all three configurations, the first harmful crash event is typically a collision with another

vehicle on the roadway. For LCVs involved in fatal crashes, 73 percent of the first harmful

events were collisions with another vehicle in transport. For STAA doubles it was an almost

identical 74 percent, and for tractor-semitrailers the number was a slightly higher 79 percent. Collisions with a fixed object — such as sign posts or bridge abutments or trees — and

collisions with a pedestrian or bicyclist were the second and third most common first event

for all three truck combinations. 

Rollovers, which includes any number of quarter turns from the upright position, are often

associated with serious traffic crashes. LCVs rolled over in 23 percent of the fatal crashes in

which they were involved, compared with 19 percent of STAA doubles, and only 12 percent

of tractor-semitrailers. 

A large majority of large truck rollovers in fatal crashes occur after another crash event, usually a collision with another vehicle. Rollovers were the first harmful crash event in only 7

percent of LCV fatal crashes, compared with 3 percent of STAA doubles, and 4 percent of

tractor-semitrailers. However, even though the percentage of first event rollovers is small,

the LCV proportion of rollovers is about twice as high as that for STAA doubles and tractorsemitrailers. One explanation for this difference is that the greater weight of many LCVs

may raise their centers of gravity and lower the rollover threshold.

Summary

Of the 17,191 truck combinations involved in fatal crashes examined here, 221 (1.3 percent)

were LCVs. Of these, 10 were triple-trailer combinations. The operation of LCVs is limited to

very few roads. East of the Mississippi River, LCVs are allowed on only a small number of

major turnpikes, except in Michigan. The limitations under which LCVs operate are reflected

in the miles they travel. According to the 1997 highway cost allocation study conducted by

the FHWA, LCVs accounted for 2 percent of all miles driven by the combination trucks in

1994. 

Based on the data presented in this brief, no conclusions can be made on the relative safety

of LCVs compared to other truck combinations. First, data on mileage driven mentioned

above are based strictly on trailer number and length, while the definition of LCV used in

this study is based partly on weight. Second, since travel by LCVs is rare, it is difficult to calculate the precise number of miles driven. Similarly, LCV fatal crashes are so infrequent that

the number varies greatly from year to year. For example, LCV crashes dropped from 46 in

1992 to 31 in 1993 (down 33 percent), then rose to 43 in 1994 (up 39 percent). Based on the

existing data, LCVs do not appear to be considerably more or less safe than other combination trucks. A more definitive conclusion could be reached only after further collection of

September 1999 data and additional analysis.

Publication No. FHWA-MCRT-99-018