Assessing the Benefits of Incident Management Systems

Most studies that evaluate the benefits of incident management have used analytical techniques such as queuing and shock wave analyses to assess the impacts of incidents with and without incident management on delays and queues. These analytical methods have been applied to basic highway segments with no consideration of the facility configurations. In addition, the analyses in most cases assumed a constant typical capacity on these segments to represent the prevailing capacities without the use of Highway Capacity Manual (HCM) procedures. These studies also assumed that input parameters such as the reduction in capacity due to incidents and incident duration are deterministic rather than stochastic variables. This paper investigates estimating the benefits of incident management by combining HCM freeway analysis procedures, detailed data archives of intelligent transportation systems, and a consideration of the stochastic variations of key inputs to the analysis rather than the use of deterministic values. The results from this analysis methodology are compared to those obtained by using the simple deterministic queuing analysis procedure, which has been used extensively in past studies. The analysis reveals that the HCM procedures produce similar results as queuing analysis for simple basic freeway facilities. The results for more complex cases indicate that queuing analysis produces lower incident delays relative to the HCM procedures because it does not model the interactions between segments of different types and geometries. Higher delay reductions resulting from incident management are estimated for one-lane blockage incidents with the use of stochastic incident attributes compared to the use of deterministic incident attributes.