The purpose of this document is to help Federal, State, Tribal, and local agencies understand the benefits of utilizing IHSDM’s quantitative measures of roadway safety in the RSA process. Three RSAs were conducted using IHSDM to identify potential benefits. The RSA team’s utilized data provided and developed designs of the existing roads to apply three IHSDM modules. The RSA teams then used the output of those modules to aid in selecting sites for detailed review and to prioritize areas where improvements should be considered. The use of IHSDM enabled the RSA teams to identify potential crash factors, or combinations of crash factors, in advance of the RSA, and to calculate the effects of potential countermeasures in terms of expected crashes, predicted operating speeds, SSD, etc. It also improved the potential for the RSA team to identify and prioritize those locations that pose the greatest crash risk, not just locations experiencing crashes. This highlighted the need to address some crash types in a more systemic manner.

Several benefits were found by using IHSDM in the RSA process. In addition to providing quantitative assessment features, the use of IHSDM helps RSA teams focus efforts, especially on longer corridors where completion of an RSA would be time and cost prohibitive. The use of IHSDM on long corridors also fosters a "holistic" look at safety that considers crash risk, not just reported crashes. This systemic approach to safety provides a method to address safety on a larger scale by applying wide scale low-cost countermeasures systemically. However, there can be challenges to using IHSDM in the RSA process. One of the biggest challenges is obtaining and entering geometric data on post-construction (existing facility) RSAs, which can significantly increase the cost of the RSA. Considering these factors, RSA projects that could benefit from the use of IHSDM include the following:

• RSAs on two lane highways where geometric data are readily available and are long sections of road that would benefit from a systemic review of safety (for use of all modules).
• RSAs on multilane rural highways, urban and suburban arterials, and freeway segments and interchanges where geometric data are readily available and are long sections of road that would benefit from a systemic review of safety (for use of the Crash Prediction Module only).

As the case studies in this document demonstrate, IHSDM can be a useful tool in the RSA process and it is recommended that IHSDM continue to be incorporated with RSAs. Enhancements to IHSDM will facilitate this process, such as providing the user with ability to select linear referencing units (i.e., project stationing or milepost referencing) and convert between selected systems. Other enhancements include providing the ability to review IHSDM results for different modules in one graph, map, or other form of output.

An "RSA Module" could be added to IHSDM, which would add the FHWA RSA Prompt Lists as default lists to this module. By running an initial evaluation of this type on a project, IHSDM users would receive prompts relevant to their projects to review. By running a secondary evaluation they would be able to add the results of their investigations to the prompt list. It is recommended that additional RSAs are conducted and documented, incorporating these enhancements and using other IHSDM modules, such as the Intersection Review and Traffic Analysis modules, not utilized as a part of the RSAs conducted for this project.