Guidelines for Traversability of Roadside Slopes

Geometric design practitioners in state transportation agencies have a new set of guidelines on probability of vehicle rollover based on various roadside design features. NCHRP Research Report 911: Guidelines for Traversability of Roadside Slopes will assist practitioners in the reduction of serious injury crashes associated with rollovers on roadside slopes.

Data from the National Automotive Sampling System (NASS) Crashworthiness Data System (CDS) shows that one-third of single-vehicle run-off-road (SVROR) crashes result in rollovers—the leading cause of fatalities in SVROR crashes. Three-quarters of these rollover crashes involve vehicles digging into the ground on embankments or in ditches after encroaching onto the roadside. Additionally, according to NASS data, pickup trucks, utility vehicles, and vans are overrepresented in rollover crashes due to higher centers of gravity. An increase in the percentage of light trucks in the vehicle fleet necessitates additional research and updates to the roadside safety guidelines.

The researchers conducted 43,000 simulations for various combinations of roadside slope configurations and geometric conditions that represent real-world crash scenarios. 

The results helped to produce this guidance on the traversability of roadside slopes for a variety of roadside conditions—shoulder width, foreslope, and foreslope width. The guidelines are presented as probability of vehicle rollover that is defined as a function of various roadside design features.