By Keith Knapp, Former Director of Transportation Safety Engineering for the Center for Excellence in Rural Safety
This article originally appeared in Rural Safety News in 2010, a newsletter of the Center for Excellence in Rural Safety (CERS) at the University of Minnesota. Rural Safety News reports on the latest research and resources concerning rural safety. View the full newsletter issue here.
Borders often are drawn between rural and urban areas to compare roadway safety characteristics and sometimes to disperse funding. According to a June 2008 article in the U.S. Department of Agriculture magazine Amber Waves, more than two dozen definitions of rural are used by federal agencies.
Our focus at CERS is rural roadway crashes. In 2007, the National Highway Traffic Safety Administration (NHTSA) determined that 23 percent of the U.S. population lived in rural areas and 57 percent of roadway crash fatalities were rural.
But just what is a rural roadway?
The true definition of a rural roadway is in the eye of the driver—they know one when they see it. A number of changing roadway characteristics, such as the posted speed limit, existence of curbs, proximity of development to the roadway, and land-use density, influence the determination if a roadway is in an urban or rural area.
We also do know that the choice of speed by a driver is connected to roadway environmental and geometric characteristics. Changes in these characteristics can be gradual or abrupt, and the location of the changes can move from year to year. Safety concerns often occur when the actual or desired roadway environment doesn’t match the driver’s perception and subsequent vehicle speed choices.
The U.S. Census Bureau defines rural as any territory outside an urban area. Since the 2000 census, the U.S. Census Bureau has included in this definition any territory outside those with populations of at least 2,500 people (e.g., urban clusters and urbanized areas). Rural and urban crashes in NHTSA’s Fatality Accident Reporting System (FARS) database are defined by their functional class designation.
U.S. Code Title 23 and Federal Highway Administration (FHWA) guidance related to setting urban and rural functional classes for roadways generally define urban areas as those with populations of 5,000 or more. More specifically, the urban or rural classification of a roadway segment is determined by the boundaries of the Federal-Aid Urban Areas (FAUA). State and local officials cooperatively assign these boundaries, with the final decision approved by the U.S. Department of Transportation. The urban area boundaries defined by the U.S. Census Bureau can be expanded to define the FAUA.
One of the prime sources for data about property damage, injury, and fatality incidents is the crash report. Access to information about the FAUA in each state by those that complete, code, and/or quality-check crash reports is important. This information, combined with how and when the rural or urban designation of a crash is made, likely impacts what is in the FARS database. NHTSA has found what appear to be some inconsistencies in the coding of urban and rural crashes in FARS.
It is difficult to apply a rural-urban boundary or line to roadway locations that can change from year to year and are defined by characteristics that can vary almost continuously. Whatever the definition of rural, however, it is generally understood that rural roadways have higher-severity crashes at a greater rate than urban roadways.
From a safety perspective, the definition of a rural roadway could include a number of factors and vary with the focus of the safety program being considered. An example of these factors might include some combination of operating speed or posted speed limit, roadside design, “curviness,” access density (or land-use density), traffic volume, and certain cross-section elements.
For safety programs related to behavioral changes and emergency response, some of the characteristics noted above also might be combined with measures of isolation or other criteria that help define areas or populations with less-than-desirable highway safety habits, such as low seat-belt use or increased drinking and driving.
Clearly, the definitions of rural proposed above are more specific and complex than the current population-based definition. The data to support such changes, however, continue to improve in quality and ease of access. In addition, transportation safety professionals are much better informed about factors that affect roadway safety and safety improvement measures. Together, these capabilities could provide the foundation for a new and more flexible definition of rural than is currently applied.
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