Vehicle dynamics modeling and simulation for the safety evaluation, selection and placement of cable barrier systems

Run-off road crashes comprise about one third of traffic fatalities. Roadside and median safety barriers are installed to safely contain or redirect the colliding vehicles in these crashes where applicable. They are intended to minimize the impact severity and the resulting injuries or fatalities. There are a large variety of roadside barriers (e.g. guardrails, concrete barriers, cable barriers, end terminals, etc.) but cable barriers remain the most common used on roadside or highway median proceeded by unlevel terrain like V-shape. These barriers have shown better results in term of injury rate, vehicle containment and post-impact vehicle trajectory. While the success rate of cable barriers is reported to be more than 90%, some crash investigations noted occurrence of vehicle-riding or over-riding the barrier, crossing the median, and penetrating into the opposite traffic lanes. The safety performance evaluation of these barriers requires a thorough understanding of the full vehicle orientation and attitude within the V-shape. CarSim vehicle dynamics program is used along with surface models of roadside topographies/terrain, based on AASHTO roadside design guides. Extensive dynamic simulations are conducted to determine the interface of vehicle – cable barrier. Dynamic simulations include various vehicle types and sizes, different initial speeds, and a variety of realistic run-off road trajectories. The simulation results were aggregated into five categories corresponding to five different sloped medians. They clearly show that there is an area from about 1’ to 7’ from the center of medians with 4:1 and from about 2’ to 5’ from the center of medians with 6:1 side slopes where placement of generic cable barriers is not recommended because of risk of under-riding. The results could also develop clear guidelines for the installations and lateral position within the median of the selected roadside barriers to ensure their optimum safety performance.