Today’s blog provides details of the newly added network screening performance measures within RoadSafe GIS for calculating high collision intersections. Check out our previous blog post for an overview of network screening and the Highway Safety Manual (HSM). Another excellent resource that we previously overlooked is the FHWA’s HSIP manual. Unlike the HSM, the HSIP manual is freely available and contains many of the same details outlined in the HSM. The manual clearly outlines the data requirements, safety performance functions, regression to the mean phenomenon, Empirical Bayes methodology, and other aspects of network screening.

For local agencies, especially in urban areas, intersections are typically the main focus of network screening measures. Therefore we have integrated this capability into our high collision intersections query. The available performance measures are dependent on the local data you have provided. The default performance measures available to all users are the average crash frequency and EPDO average crash frequency.

Data needed for the other performance measures include:

  • ADT – crash rate, critical rate, method of moments
  • Intersection infrastructure (ex. signalized/non-signalized) and reference populations – relative severity index, probability of crash types exceeding threshold proportion, excess proportion of specific crash types.


Although the HSM recommends using the performance measures with locally calibrated SPFs and EB adjustments, the reality is many agencies do not have the data required for those performance measures. RoadSafe GIS provides a means to calculate the other performance measures that your agency is more likely to have the data to support. Over time as you collect more data for ADT or intersection infrastructure the system can be updated to give acces to those safety performance measures. RoadSafe GIS is flexible and we will work with you to incorporate the data you have available while maximizing your ability to identify high collision intersections with the best potential for collision reduction.

If you are interested to learn more about the network screening performance measures for intersections available in RoadSafe GIS or would like to try out a demo, contact us at



Co-Founder of RoadSafe GIS. Bringing collision data, GIS and cloud technology together. Formerly of UC Berkeley SafeTREC and ESRI.