In the project development process, transportation engineers assess the effect of roadside designs and features on crashes. The Highway Safety Manual (HSM) provides scientifically sound information to support this decision making through Crash Modification Factors (CMFs), which provide an indication of the safety effect of specific design elements known to have an influence on the frequency or severity of crashes. However, few roadside CMFs exist and those that do exist were not typically of the statistical quality deemed appropriate for inclusions in the First Edition of the HSM. The Roadside Design Guide (RDG) provides a probability of encroachment model to quantify the safety of a roadside design and compare the design against other designs. Software support for the HSM is provided through the Interactive Highway Safety Design Model (IHSDM) and for the RDG through the Roadside Safety Analysis Program (RSAP). Research is needed to review the two methods, document inconsistencies in predicting the frequency and severity of run-off-road crashes, provide recommendations to update the models to improve consistency and provide guidance to practitioners on using each method at various highway planning and design stages. Such research should also consider the possibility of incorporating RSAP with the IHSDM and identify a critical set of CMFs that would support the quantification of changes to the roadside and the installation or modification of roadside features, eliminating the need to use the subjective hazard ratings. It should also develop these CMFs for inclusion in a future edition of the HSM. It is expected that the methods used to develop the CMFs will meet the scientific protocol acceptable for inclusion in the HSM and FHWA CMF clearinghouse.
The objective of this research is to develop quantitative measures that can be incorporated into the HSM to evaluate the effects of roadside designs and features on the frequency and severity of lane departure crashes. The project includes the following tasks: (1). Conduct a literature review of the analysis methods to quantify lane departure crashes including those used in the HSM and RSAP. (2). Identify CMFs and available data sources related to lane departure crashes from completed and ongoing research projects. (3). Survey practitioners, researchers, design consultants, and transportation agencies to assess their current model uses and needs as they relate to roadside safety during the planning and design stages. The survey should also solicit input about specific roadside concerns or areas of need regarding additional CMFs. (4). Document the strengths and weaknesses and differences between the HSM prediction models and RSAP and identify opportunities to provide consistency through updating data sources, base models, or modification factors. (5). Analyze sample scenerios for comparison between the HSM prediction models and RSAP. These scenerios should consider: rural 2-lane (level, rolling, and mountainous terrain), rural multilane (level, rolling, and mountainous terrain), and urban arterial. Long and short segment lengths as well as planning and design should be considered. (6). Develop recommendations that as a minimum address: (1) model applicability; (2) appropriatness of continued parallel development of both methods for roadside safety assessment or, if one method should be chosen, for future development efforts; and (3) methods and coding for the possible inclusion of RSAP as a module in the IHSDM. (7). Develop a prioritized list of roadside CMFs that should be evaluated for development and possible inclusion in future versions of the HSM. (8). Submit an interim report that includes the findings from Tasks 1 through 7 and an updated work plan. (9). Develop objective CMFs using the HSM protocols for the base conditions outlined in Volumes 2 and 3 of the Highway Safety Manual. (10). Depending on the outcome of Task 6, prepare recommendations for potential modifications to the RSAP model. (11). Submit a final report documenting the entire research project. CMFs developed from this research should be documented in separate appendices that include, as a minimum, data sources, sample size, and analysis methodology.
STATUS: Research in progress; Phase 3 underway.