U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
The results of data analysis will provide a summary of the crash frequency and rates on the roadway network and can highlight associated crash factors. The next step is to determine the most appropriate treatments to install to reduce the number and severity of crashes.
To make the most informed decisions regarding countermeasure selection, an agency should begin with the crash history data when available. Common crash types, the severity of the crashes, and the location of those crashes are 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 most appropriate implementation approach. 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. Systematically applying safety treatments based on factors other than crash location can prevent future crashes for locations that have yet to experience them.
If roadway characteristic information is known, systematic solutions can be installed effectively, even if there are gaps in the crash data. Analysis shows that, in some situations, a high proportion of crashes tend to occur at locations that share common geometric or operational elements.12 Installing the same countermeasure at multiple locations (where appropriate) could be an effective strategy to improve safety.
The basis for the systematic approach is not on specific crash locations, but on crash types and proven low-cost safety countermeasures. In one application of the systematic approach, common crash types are determined and countermeasures are selected that address the specific types. The network is screened for locations experiencing those crash types or that have the potential for them to occur. Selected safety solutions are then installed systematically at identified locations.
Another application of the systematic approach begins with the selection of low-cost, effective countermeasures to common traffic safety issues. Once strategies are identified, the crash data system is searched to find locations where the countermeasure can be cost-effectively deployed. Estimates of the impacts of implementation can be made in terms of deployment cost and the benefits measured in traffic crash reduction.
Benefits of the systematic approach may include:
Drawbacks of the systematic approach may include:
The spot location approach has typically been based on an analysis of crash location history. Due to the fact that some locations in a jurisdiction will likely have a significantly higher number of crashes than most of the others, it is important to identify those locations and treat them accordingly.
The benefits to the spot location approach may include:
Drawbacks of the spot location approach may include:
The spot location approach to traffic safety can be implemented in parallel with the systematic approach to provide a combination of safety treatments in a jurisdiction. In addition, the spot location approach could be applied to those locations that have had low cost countermeasures installed systematically, but continue to show a higher than average crash rate.
The comprehensive approach introduces the concept of the "4 E's of Safety":
This approach recognizes that not all locations can be addressed solely by infrastructure improvements.
Some locations will be identified that have frequent driving violations for which targeted enforcement is an appropriate countermeasure. In general, human behavior issues (e.g., speeding, aggressive driving, failure to wear safety belts, driving while impaired) are a factor in a high percentage of crashes. When locations are identified that have reports and observations of these violations, coordination with the appropriate law enforcement agencies is needed to deploy visible targeted enforcement to reduce the potential for future driving violations and related crashes. Additionally, educational efforts should supplement enforcement to improve the effect of each.
Using the example of County Road 220, analysis showed that five of the 12 crashes involved alcohol on a weekend evening. In this case, the practitioner should coordinate with the local law enforcement agency to consider additional alcohol-focused enforcement on the weekends on this roadway.
Countermeasure selection is a data-driven process, focused on not only crash history, but also on roadway elements to determine the appropriate strategies. Roadway configuration contributing to crashes is often recorded in the crash database and/or police reports. Through examination of the reports or through field reviews these can be identified and factored into the countermeasure selection process. For example, County Road 220 had 12 crashes in the past 5 years. Further study of the crash database indicated that eight of those 12 crashes occurred at intersections. With this information available, the practitioner can implement countermeasures that address safety issues at intersections on this route, and potentially at similar locations on other routes within the jurisdiction.
Additional information on data analysis for selecting countermeasures to be considered can be found in Appendix B.
It is important to evaluate traffic safety treatments after installation to determine their effectiveness. The effort that goes into conducting the assessment will help guide future decisions regarding safety treatment implementation.
A record of crash histories and countermeasure installations forms the foundation for assessing how well implemented strategies have performed. It is important to keep a current list of installed countermeasures with documented "when/where/why" information. Periodic assessments will provide the necessary information to make informed decisions on whether each countermeasure contributed to an increase in safety, whether the countermeasure could or should be installed at other locations, and which factors may have contributed to the strategy's success.
To perform the assessment it is necessary to collect the required information for a certain amount of time after strategies were deployed at the intersection. The time period varies, but should be no less than one full year (with 3 years preferred). The most important information is crash data before and after implementation. Other information required may consist of public input and complaints, police reports, and observations from maintenance crews.
It is important to keep the list of deployed strategies up to date since it will serve as a record of countermeasure history. By using this type of system, assessment dates can be scheduled to review the crashes and other pertinent information at locations where treatments have been installed.
12 Federal Highway Administration, Low-Cost Safety Enhancements for Stop-Controlled and Signalized Intersections, FHWA-SA-09-020, May 2009. [ Return to note 12. ]