Dynamic Hard Shoulder Running for Traffic Incident Management

Hard shoulder running (HSR), used in many large cities for reducing peak hour recurring congestion, has been proved effective. This paper looks at another perspective of using hard shoulders and proposes dynamic hard shoulder running (D-HSR) for traffic incident management. The purpose of this paper is to show the benefits and make recommendations to state departments of transportation and local agencies on how to use hard shoulders dynamically to reduce the effects of nonrecurring traffic incidents. An approach based on microscopic simulation with factorial experimental design is adopted in this study, and interesting results are obtained from the discussion and statistical analyses of simulation results: (a) D-HSR strategies are more suitable for property damage only incidents in which traffic operations centers have more flexibility in managing traffic; (b) only the part of the shoulder that is 0.5 mi upstream and downstream of the incident location needs to be opened to achieve maximum benefits for relieving a bottleneck; (c) the opened shoulder can be closed after the incident is cleared, and opening the shoulder for a longer time will not improve traffic conditions; and (d) the effectiveness of D-HSR is significant across different roadway geometry, traffic, and incident scenarios. Equations to estimate potential benefits are also available in this paper. These results are favorable particularly in practice because shoulders need to serve as refuge areas for incident vehicles and be used by emergency vehicles. It is recommended that departments of transportation and local agencies consider D-HSR for relieving congestion during incidents.