NCHRP Report 440, "Accident Mitigation Guide for Congested Rural Two-Lane Highways," will assist planners, designers, and traffic engineers in identifying and designing projects to improve safety on congested rural two-lane highways. The guide assumes that widening the road to four lanes is not a practical solution because of financial, environmental, or societal constraints. Geometric, traffic-control, and other types of countermeasures are discussed. This guide will assist the practitioner in (a) identifying current and potential problem locations for detailed analysis, (b) isolating accident types and contributing factors, (c) matching countermeasures to accident types and contributing factors, and (d) assessing the effects of applying the countermeasures. The guide presents an accident-mitigation process, describes many countermeasures and their effects, presents examples of safety improvements, and suggests further readings.

Two- and three-lane (two through lanes plus a passing or turning lane) highways can become more congested because of growing communities in exurban areas, heavy recreational travel, seasonal residencies, and special events. As daytime congestion increases, the potential for accidents and the proportion of fatal and injury accidents also increase. Because of financial, environmental, and societal constraints, state and local transportation agencies may be unable to mitigate these accidents by widening the road.

Under NCHRP Project 17-15, the Texas Transportation Institute and Midwest Research Institute identified accident types that are prevalent in congested conditions and countermeasures that are likely to reduce the frequency or severity of accidents on two- and three-lane roads. The agencies also collected safety, geometric, traffic, and other data at several sites to assess the effectiveness of various countermeasures. A broad range of countermeasures was evaluated, from geometric improvements to traffic control to enforcement to public information.