Design Treatments to Reduce Nonrecurrent Congestion

Individuals and businesses rely on predictable travel times to ensure that people and goods arrive at their destinations on time; however, travel times are often unpredictable due to nonrecurrent congestion. Unlike recurrent congestion, which occurs on a daily basis during peak traffic periods, nonrecurrent congestion results from unpredictable causes of delay. The six key sources of nonrecurrent congestion considered in this research are: Traffic incidents, Work zones, Demand fluctuations, Special events, Traffic control devices, and Weather. Because of nonrecurrent congestion, travelers may find that the same trip requires substantially different travel times on different days, making it difficult to arrive at work on time, make deliveries on time, and plan efficient travel routes. This is frustrating to motorists and has substantial economic consequences to industries that depend on just-in-time deliveries. A major research effort is under way in the United States and other countries to find ways to increase travel-time reliability and make travel times more predictable. As part of the Reliability area of the Strategic Highway Research Program (SHRP 2), which focuses on the need to increase travel-time reliability, SHRP 2 Project L07, Identification and Evaluation of the Cost-Effectiveness of Highway Design Features to Reduce Nonrecurrent Congestion, is identifying and evaluating a broad range of design treatments to reduce nonrecurrent congestion. These include innovative median treatments, shoulder treatments, ramp treatments, detour treatments, work zone treatments, treatments that address animal-vehicle collisions, and treatments that minimize the impact of severe weather events. This paper describes many of the treatments identified for evaluation in Project L07 and shows how they may be used to reduce nonrecurrent congestion.