Roadway departure crashes account for half of all fatalities—over 18,000 annually—with more than 5,000 fatalities resulting from head-on crashes. These crashes primarily occur on two-lane paved, undivided, high-speed rural roads where vehicles travel in opposite directions and are often separated only by a center line pavement marking and, in some cases, a rumble strip. This type of roadway comprises approximately 69%—1.97 million center line miles—of roads across the country.

NCHRP Research Report 995: Guidelines for Treatments to Mitigate Opposite Direction Crashes identifies center line buffer areas—which provide additional space between opposing traffic on undivided roads—and cable median barriers on divided highways as effective treatments for reducing serious head-on crashes. Another alternative, implemented at a limited number of locations nationally, combines these treatments by installing center line barriers on previously undivided roadways. While some of these installations do not provide the full barrier deflection distance, a report from an installation in Oregon found positive results in reducing head-on crashes.

Research is needed to evaluate the effects of center line barriers on lane departure crashes, operating speeds, first responder activities, property access, provisions for passing, and tradeoffs with lane or shoulder width reductions required for installation and maintenance. Research is also needed to understand the types of roadways where a center line barrier might be considered, suitable barrier types, space requirements (to balance the risk of opposite-direction crashes), and best practices for mitigating impacts.

The objective of this research is to investigate the use of barriers along the center line of previously undivided roads. The research will evaluate the national and global state of the practice, identify locations where a center line barrier has been installed, and document the effects on all crashes and severe injuries by developing crash modification factors. Of particular interest will be the occurrence of crashes when the full working width of the barrier is not provided.