The Effects of Truck Size on Driver Behavior

Seguin, E. L.; Crowley, K. W.; Harrison, Paul C. Jr.; Perchonok, Kenneth · 1982 · ROSA P / United States. Department of Transportation. Federal Highway Administration. Office of Research

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Summary

This 1982 Federal Highway Administration report investigates whether increases in truck size—specifically length/configuration and width—cause undesirable or unsafe behavioral changes in drivers of other vehicles. The study was motivated by the 1973 national speed limit, which spurred lobbying for larger truck dimensions, and the counter-argument that larger trucks increase accident risk. The research aimed to define car-truck interaction areas where truck size might influence driver behavior, identify such changes, and suggest remedial techniques. The study employed four field experiments using the Traffic Evaluator System (TES) to collect microscopic traffic data, supplemented by observer records of erratic maneuvers. Three studies focused on truck length/configuration (short single, long single, double, and triple trailers) in a freeway entrance merge, a narrow bridge, and a mainline lane-change weaving section. One study focused on truck width (96, 102, 108, and 114 inches) in a rural two-lane passing situation, using an experimentally widened truck to induce passing. Data collection faced significant technical challenges; TES hardware failures rendered data from high-volume freeway and lane-change sites largely unusable, limiting those analyses to low-density conditions or observer-only data. Findings indicated that truck length/configuration had little to no measurable effect on interacting drivers in the merge, bridge, and lane-change scenarios. In the truck width study, increasing width was associated with increased pre-pass headways, reduced lateral distances between passers/oncomers and the truck, and reduced lateral distance from the road edge. However, no significant increase in the acceptance of small, unsafe gaps was found. While lateral separations decreased with wider trucks (down to 39 inches in worst-case scenarios), there was no evidence that wider trucks increased the likelihood of shoulder encroachments. The only notable behavioral differences in the length studies involved triple trailers, which elicited more braking and lane changes, but these effects were likely confounded by the slower speeds of the specific triple trailer used in the study rather than the configuration itself. The study concludes that automobiledrivers generally do not perceive differences in truck size or react unusually to them in the selected roadway situations. There is no evidence of serious hazards imposed on non-truck drivers due to increased truck size in these contexts. The authors recommend that current size limits be maintained, noting that the lack of observed negative behavioral effects supports the safety of larger trucks, provided that standard operational practices are followed. The report highlights the need for improved data collection systems to handle high-volume traffic conditions for future research.

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• traffic density

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• Empirical Findings: behavioral performance data