Longer Combination Vehicles Involved in Fatal Crashes, 1991-1996
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Longer Combination Vehicles Involved in Fatal Crashes, 1991-1996

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      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, there-fore, 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. Alco 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 truck-tractor, 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.
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