Crash cushion selection criteria
Crash cushions are used as a roadside safety treatment alternative to protect errant vehicles from striking potentially hazardous roadside fixed 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. This research study aims to quantify the life cycle costs of different crash cushion systems installed across the state of 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, was used to estimate the frequency of run-off-the-road collisions under different scenarios for one-way, undivided, and divided highway facilities. The estimated impact frequency based on pertinent inputs was then used as a decision criteria to select the most appropriate cushion category. Two general crash cushion categories were defined. These included redirective cushions with higher installation and lower repair costs and redirective cushions with lower installation and higher repair costs. The life cycle cost comparison indicated that the low-installation/high-repair category was optimum until an impact frequency of approximately 0.08 per year, beyond that value, high-installation/low-repair tended to be more cost-effective.