Real-Time Analytics of Transportation Data Lab

About the research

The Iowa Traffic Safety Improvement Program (TSIP) allocates funding from state fuel tax revenues for site-specific road safety improvements, the installation of traffic control devices, and studies and outreach. Demand for these funds is increasing as Iowa Department of Transportation (DOT), county, and municipal governments continue to redouble their roadway safety efforts. Consequently, the TSIP application process is increasingly competitive.

Currently, agencies applying for site-specific safety project funding are required to complete an engineering economic analysis spreadsheet. This process begins by estimating the magnitude of the safety problem at the candidate location using crash data from recent years. Applicants then estimate the anticipated crash reductions associated with the proposed intervention. Next, monetary values are assigned to the crash reduction benefits. In the final step, this amount is compared to the project cost to derive a benefit/cost ratio. This ratio serves as a key metric for comparing candidate projects to one another, to help guide TSIP project selection decisions.

Several technical issues can arise in this process, creating potential inconsistency among applications. The TSIP Process Improvement Phase I project identified the most appropriate crash modification factors (CMFs) for use in Iowa (i.e., the factors used to determine the  proportion of crashes each type of improvement is likely to eliminate). Beyond the work completed in Phase I, several issues warranted further investigation, such as the appropriate monetary values for various crash severity levels, how to compare per-crash values with per-injury values, how to account for uncertainties in the underlying crash data, how to keep economic analysis assumptions updated, and whether to convert from a spreadsheet-based application to an online application.

In addition to administering the TSIP application process, the Iowa DOT is currently exploring methods for consistently incorporating safety analysis across all highway improvement projects. Crash costs are an integral part of these analyses. Thus, it is likely that crash valuations and methods established for TSIP will be influential in other safety analyses, screening applications such as the intersection Safety Improvement Candidate Location list, and applications of a crash prediction tool that is currently being developed.