U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Substantive safety is defined as the actual long term or expected safety performance of a roadway. This would be determined by its crash experience measured over a long enough time period to provide a high level of confidence that the observed crash experience is a true representation of the expected safety characteristics of that location or highway. Quantitative measures of substantive safety include:
Expected safety performance will vary based on inherent differences among highway types and contexts. For example, the frequency and other characteristics of crashes differ for a two-lane road in rolling rural terrain versus a multi-lane urban arterial versus a freeway interchange.
Understanding a location’s substantive safety and making judgments about whether it meets expectations should involve formal comparison of its crash profile with aggregate data for facilities with similar characteristics—traffic volume, location (urban, rural, suburban), functional classification, facility type (two-lane, multi-lane divided, etc.), and terrain. There are well–established methods for characterizing a location’s substantive safety. This generally includes applying statistical models of crash experience from broader data bases (safety performance functions and accident modification factor analysis). It should be based on models and data from the same jurisdiction of the site being studied. See "Resources to Support Substantive Safety Analysis and Decision Making" on page 1-8 for more information.