This document examines the way in which the Highway Safety Manual (HSM) has made predictive safety analysis feasible for many basic roadway elements, including freeway and ramp segments and ramp terminals. This capability raises the expectation for predicting the safety performance of more complex roadway facilities, such as interchanges. Although interchanges can be decomposed into basic road elements, the safety performance of interchanges cannot be derived by simply adding predictions from individual components.

The Federal Highway Administration (FHWA) supported a project to explore planning-level analysis of interchange configurations during alternatives analysis or Interchange Access Requests (IARs). FHWA sought to identify the most commonly considered configurations in IARs and develop a predictive model and implementation tool. The purpose of this predictive model and associated implementation tool is to use an approach with more robust considerations than a single crash modification factor and provide reliable predictions using information commonly known during interchange project planning. The model and implementation tool can be used to evaluate the predicted crash frequency and severity for interchange configurations under consideration using basic inputs for the entire interchange area.

This report documents the methods and processes used to identify applicable service interchange configurations for inclusion in the predictive method and provides details on data collection procedures and methods used for developing crash frequency and severity implementation models. The results of this research can be used to support planning-level analysis of various interchange configurations under consideration early in the project development process.

Recommended citation: Federal Highway Administration, Safety Comparisons Between Interchange Types (Washington, DC: 2023) https://doi.org/10.21949/1521993