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 was 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.
Research complete; final report pending publication.