Guidelines For Traversability Of Roadside Slopes

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.

Roadside Design Guide

"The Roadside Design Guide presents a synthesis of current information and operating practices related to roadside safety and is written in dual units-metric and U.S. Customary. This book is a guide. It is not a standard, nor is it a design policy. It is intended to use as a resource document from which individual highway agencies can develop standards and policies. Although much of the material in the guide can be considered universal in its application, several recommendations are subjective in nature and may need modification to fit local conditions. However, it is important that significant deviations from the guide be based on operational experience and objective analysis. The 2011 edition of the AASHTO Roadside Design Guide has been updated to include hardware that has met the evaluation criteria contained in the National Cooperative Highway Research Program (NCHRP) Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features and begins to detail the most current evaluation criteria contained under the Manual for Assessing Safety Hardware, 2009 (MASH). For the most part, roadside hardware tested and accepted under older guidelines that are no longer applicable has not been excluded in this edition." -- AASHTO website.

Safety Aspects of Roadside Cross-section Design