U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Horizontal curves make up a small percentage of total road miles, yet account for one-quarter of all highway fatalities. The majority of curve-related crashes are attributed to speeding and driver error and involve lane departures. There are a number of low-cost countermeasures traditionally used to help keep vehicles on the road and in their lane; however, the impacts of their application can be limited, which leads to the need for additional research and testing on more dynamic devices to assist traffic engineers in managing speed and safety across their diverse roadway network.
More than 25 percent of fatal crashes are associated with a horizontal curve, and the vast majority of these crashes involve a roadway departure. The average crash rate for horizontal curves is about three times that of other highways segments. About three-quarters of curve-related fatal crashes involve a single vehicle leaving the roadway and striking trees, utility poles, rocks, or other fixed objects, or overturning. The majority of these crashes are speed related.
Implementing safety countermeasures on rural horizontal curves to address speeding can improve the safety performance for those locations. State safety and traffic engineers are faced with making decisions on what type of technology to use and which sites to use the technology on in a fiscally constrained environment. The research conducted for this project will evaluate a Sequential Dynamic Curve Warning System (SDCWS) that could be an additional tool for these engineers to use either separately or in combination with other countermeasures to address horizontal curve locations with a history of safety concerns.
The objective of this project is to test and evaluate the effectiveness of TAPCO's SDCWS in reducing vehicle speed as well as the frequency and severity of speed-related crashes on horizontal curves on rural roadways. With 12 treatment sites and 24 control sites having been identified in Missouri, Texas, Washington, and Wisconsin, speed data will be collected before and immediately after the installation, as well as at 12 and 18 months post installation.
The information in this interim report includes a summary of the literature on speed-activated display practices, details on the locations of existing treatments, site selection methodology, a list of potential and final new treatment sites, the type and amount of data to be collected, data collection procedures and equipment, and the schedule for analyses to be performed. The report also includes a summary of baseline data including roadway, traffic, and crash data and data analysis and results from the 1-month post installation data collection effort. Guidelines and recommendations for implementing SDCWS displays for curves will be included in the final report.