HSIS Summary Report
Graham, J., K. Richard, M. O’Laughlin, and D. Harwood
Jan-11
When a vehicle leaves the traveled way and encounters a pavement-shoulder drop-off, it can be difficult for the driver to return safely to the roadway. As the driver attempts to steer back onto the pavement, the side of the tire may scrub along the drop-off, resisting the driver’s attempts. This resistance often leads the driver to overcorrect with more steering input. When the tire finally remounts the pavement, the larger steering angle may cause the vehicle to “slingshot” across the road. This can result in a head-on collision with other traffic or a loss of control and overturning of the vehicle on the roadway or roadside. The safety edge is an innovative treatment intended to minimize drop-off-related crashes. With this treatment, the pavement edge is sloped at a 30-degree angle (see figure 1). This angle makes it easier for a driver to safely reenter the roadway after inadvertently driving onto the shoulder. Research conducted by Texas Transportation Institute (TTI) in the 1980s found that drivers rated a 45-degree wedge as a much safer pavement edge to remount than either the vertical or rounded edges normally found with portland cement concrete and asphalt pavements.(1) Because drivers in the study were instructed to drive off the pavement edge, the TTI research has been criticized as not being representative of naïve drivers. Prior to this research, neither an actual field evaluation of the safety edge nor a formal effectiveness evaluation had been completed.
Safety Evaluation of the Safety Edge Treatment
safety edge
drop off
run off road
steering
head on
wedge
HSIS Summary Reports are two to eight pages in length and include a brief description of the issue addressed, data used, methodology applied, significant results, and practical implications.
A variety of research studies have been performed using data from HSIS. Many of the final reports prepared are now available electronically.
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