Dual Analysis Approaches Target Effective Ways to Improve Safety

June 14, 2011

As local, state, and federal transportation agencies strive to reduce fatal and serious injury crashes, they face the dilemma of how to identify high-risk problem areas and most effectively use limited financial resources to make improvements that will have the greatest impact.

Agencies can take two approaches to solving this dilemma and determine how best to implement changes. One approach is to identify high crash locations, and countermeasures. The second approach is to systematically and proactively implement crash-reducing design features across a roadway network.

The high-crash location approach identifies sites for safety improvements based on historical data. Agencies, using network screening, prioritize locations that show unusually high crash frequency, or “black spots.” Through this black-spot analysis, agencies can then apply countermeasures to improve safety, such as adjusting or increasing street lighting, introducing traffic signals or roundabouts, and installing pedestrian countdown signals.

This method tends to point to locations in urban areas with high traffic volumes. However, according to the 2008 Fatal Analysis Reporting System (FA RS), 55 percent of fatal crashes nationwide occur in rural areas where traffic density is low and specific high-risk locations are difficult to pinpoint.

Transportation agencies historically have used the high-crash location approach to allocate safety resources.

The systematic approach focuses mainly on implementing low-cost solutions over many miles of road. The road network is evaluated to identify and prioritize improvements based on particular types or severity of crashes. For example, if runoff- road crashes are an issue, agencies can target their investment on rumble strips and systematically implement a cost effective solution, not just at specific locations where such crashes have occurred. By doing so, agencies are proactively reducing the likelihood of crashes.

Some other examples of systematic treatments include wider striping, larger signs, delineating guardrails and creating wider shoulders. This approach allows for policy level implementation and can address situations in rural areas where traffic is light and high-risk sites are difficult to identify.

Iowa, Minnesota, Missouri and Washington are among the states that have combined the systematic approach with black-spot analysis to reduce the frequency and severity of crashes. This complementary mix of approaches has proven successful in fostering safety while judiciously applying limited financial resources

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