About the research
Crash cushions are used as a roadside safety treatment alternative to protect errant vehicles from striking potentially hazardous fixed roadside objects. A variety of crash cushion designs, with varying characteristics, are available for use by transportation agencies. The choice of an optimum cushion type in consideration of safety performance and economic viability at any given highway location depends on several factors, including roadway geometry and traffic characteristics, among others.
This research study aimed to quantify the life cycle costs of 13 different crash cushion systems installed in Iowa and to develop guidance to help decide where and when to install specific types of cushions. A probability-based tool, the Roadside Safety Analysis Program (RSAP), was used to estimate the frequency of run-off-the-road (ROR) crashes under a variety of roadway characteristics for three separate facility types, including two-lane undivided, four-lane divided, and one-way highways. The estimated impact frequency based on pertinent roadway and traffic characteristics was then used as a decision criterion to select the most appropriate crash cushion system in consideration of installation and maintenance costs.
Two general categories of redirective crash cushion systems were compared. These included crash cushions with higher installation and lower repair costs (RHL) and crash cushions with lower installation and higher repair costs (RLH). The life cycle cost comparison indicated that the RLH category was the optimal crash cushion type until an impact frequency of approximately 0.08 countermeasure strikes per year. Beyond this threshold, the RHL crash cushion category tended to be more cost-effective. Design guidelines based on hazard offset, annual average daily traffic (AADT), and curve radius are provided for each facility type of interest.