Safety of Passing Longer Combination Vehicles on Two-Lane Highways

Whether to allow wider use of longer combination vehicles (LCVs) is the topic of a policy debate in the United States. If allowed to operate in a greater number of states, LCVs would largely be confined to interstate highways and other major facilities. Yet, it often may be necessary for them to travel on two-lane highways en route to shipping points to pick up or discharge freight. A safety issue related to LCVs operating on two-lane highways is the potential risk to occupants of vehicles overtaking LCVs. To help assess the added risk of passing a longer vehicle, we developed a passing model that takes into account different performance levels of overtaking autos, varying levels of aggressiveness of drivers, volume of oncoming traffic, and lengths of vehicles being overtaken. We conclude that with moderate oncoming traffic, the odds of failure to pass a 120 ft LCV versus a 65 ft standard truck are about 2–6 times greater.