U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Highway safety decisions are generally made based on data. Regulations for safety-related Federal funding and safety plan development require data for the decision making process. Recent national initiatives, such as State-level Strategic Highway Safety Plans (SHSPs) and the High Risk Rural Roads Program (HRRRP) have contributed to improved rural road safety by fostering the implementation of effective countermeasures. One aspect of this Federal support is an emphasis on data-driven processes to help jurisdictions determine the best course of action for making safety decisions on local road networks. For example, the HRRRP requires that rural major collectors, minor collectors, and local roads exhibit a history of crashes above the statewide average or are expected to experience a higher-than-average number of crashes in the future to be eligible for Federal funding.
At the local level, these data requirements can seem daunting, particularly as they relate to funding and staff time needed for data collection, analyses, and overall assessments of safety improvements. It is important to note that a data-supported approach can increase the effectiveness of the distribution of limited funds to improve safety on local rural roads.
A comprehensive set of crash data is desirable for effective roadway analysis and countermeasure selection, but a lack of such databases should not deter road safety practitioners from addressing safety issues on their roadways. The types of information that should be collected for roadway safety analysis include crash data (location, type, severity, roadway conditions, weather, time of day, day of week, month), exposure, and roadway elements. The primary sources of these data are local law enforcement crash reports, emergency medical service information, and State and Federal databases. In addition, observational data often serves as an important supplement to formal data sources.
Collected data should be analyzed to identify locations with safety issues or locations with potential for safety issues, and to select countermeasures to improve safety. Depending on the completeness, accuracy, and timeliness of available data, a local jurisdiction can analyze that information in a number of ways. Analyses can range from simple cluster analysis to more advanced calculations of crash rates, determination of crashes by type and severity, and analysis of combinations of contributing factors and roadway elements. By using a data-driven approach, local practitioners will have the information to make informed decisions about the type and location of strategies to optimize effectiveness. Many states have developed data analysis tools; these are often shared with local practitioners to assist their local road safety programs.
Crash data, when available, can assist practitioners in making the most informed decisions regarding countermeasure selection. Common crash types, the severity of the crashes, and the location of those crashes are some important attributes of crash data for the countermeasure selection process. There are three main types of countermeasure implementation approaches - spot location, systematic, and comprehensive. The quality and availability of data can assist in determining the implementation approach undertaken. The spot location approach is the most dependent on data availability and quality. The systematic implementation of safety countermeasures may be the most effective approach for those roadways that lack comprehensive data. Analysis shows a high proportion of crashes tend to occur at locations that share common geometric or operational elements. Installing the same countermeasure at multiple locations, where appropriate, could be an effective strategy to improve safety on the overall network.
The effectiveness of specific road safety countermeasures is important to an overall safety program at any level, due to resource limitations of highway agencies. The assessment will help guide future decisions regarding the selection and implementation of safety countermeasures. Looking at the number and type of crashes before and after the implementation of a safety strategy will provide a basic effectiveness of the strategy. However, to understand the full effect, changes in traffic volumes and roadway attributes should be considered.
Local highway agencies have unique responsibilities and challenges related to the safety of their roadway system. By beginning any traffic safety effort by first looking at the data, those agencies will be in a better position to address their highway safety needs.