BACKGROUND
Each year, roadway departure crashes in the United States result in serious injuries and fatalities. Between 2012-2014, the average number of fatalities per year resulting from roadway departure crashes was 18,355. Of that number, 7,349 fatalities resulted from impacts with fixed objects such as trees, shrubbery, utility poles, luminaire poles, sign supports, and traffic signals—all classified as the most harmful events. (Source: Fatal Analysis Reporting System, NHTSA).
Current guidance directs transportation agencies to remove or avoid placing fixed objects within regions close to the traveled way. However, agencies must often consider numerous competing interests. For example, roadside trees are noted to provide environmental and aesthetic benefits. In addition, discussion of tree removal can become a contentious issue for the general public as well as specific interest groups. Overhead utilities located along the right-of-way provide essential services to residential and commercial customers, but relocation of those utilities is often costly.
As transportation agencies continue to expand the use of data-driven decision-making processes and performance-based design decisions, the need to quantitatively evaluate the safety risks posed by fixed objects located near the traveled way as well as the benefits of implementing various safety treatments within the clear zone is necessary. With recent concepts such as context-sensitive solutions, complete streets, and practical design evolving into more mainstream practices, there are many factors that must be considered and balanced in the development of the roadside environment. Transportation practitioners need a risk-based, technical approach to help mitigate fatal and serious injury crashes with fixed objects with in the right-of-way. This alternative approach will allow engineers to quantitatively and impartially balance safety with other factors as well as better communicate to decision makers and the public the safety risks posed by fixed objects placed in close proximity to the roadway.
Results of this research will enable transportation agencies to set and evaluate their level of safety risk and use quantitative information in the decision-making process. This is consistent with the approach for other guidance being developed for the next version of the AASHTO Roadside Design Guide (RDG).
OBJECTIVES
The objectives of this research were to develop an evaluation methodology and guidance for use by the transportation engineering practitioner to quantify the relative risk of collisions with roadside fixed objects. The research results are intended for inclusion as a new chapter or supplement in a future edition of the Roadside Design Guide.
The results should address a broad range of roadside safety issues considering but not limited to: traffic volume; speed; crash severity; urban and rural land use; horizontal curvature; roadway geometrics; fixed-object type, size, and offset; and fixed-object density. The effectiveness of various mitigation strategies in lieu of removal or relocation should also be considered or evaluated.
