Save Lives With the Safety Edge
Reproduced from the Federal Highway Administration (FHWA) Publication # FHWA-SA-09-023
Pavement Edges Can Pose Serious Safety Risks
Roadway departures account for 53 percent of fatal crashes. While national data documenting the role of pavement edge configuration in the sequence of events leading to crashes are not available, some State-level studies point to the life-saving potential of safety edges. For example, researchers studying crashes in Iowa during 2002-2004 reported that pavement edges may have been a contributing factor in as many as 18 percent of rural run-offroad crashes on paved roadways with unpaved shoulders. This type of crash was four times more likely to include a fatality than rural crashes overall on similar roads (Hallmark et al: Safety Impacts of Pavement Edge Drop-Offs, AAA Foundation for Highway Safety, Washington DC, Sept. 2006.)
How Pavement Edges Affect Crash Severity
When a tire drops off a paved surface, sometimes just inches from the travel lane, a driver can have difficulty re-entering the roadway if the pavement edge is nearly vertical - especially if the height difference is significantly more than 2 inches. When a driver drifts off the pavement and tries to steer back on, the nearly vertical edge can create a “tire scrubbing” condition that may result in over-steering. If drivers over-steer to return to the paved surface without reducing speed, they are likely to lose control of the vehicle. The vehicle may veer into the adjacent lane, where it may collide with or sideswipe oncoming cars, overturn, or run off the opposite side of the roadway and crash.
Increase Roadway Safety at No or Low Cost by Specifying the Safety Edge
A simple and cost-effective way to promote pavement edge safety is to adopt a standard specification for all resurfacing projects that requires a 30° - 35° angle “Safety Edge.” After paving, the adjacent material is graded flush with the top of the pavement.
Solutions to the Pavement Edge Drop-off Risk
- Require a 30° - 35° angle asphalt wedge “Safety Edge” at the graded material interface in asphalt resurfacing projects.
- Routinely resurface shoulders when roadways are resurfaced, and add the Safety Edge.
- Maintain edge drop-off depths at 2 inches or less on high-speed highways.
The asphalt wedge provides a safer roadway edge, and a stronger interface between the pavement and the graded material. The additional cost of the asphalt wedge is minimal when included as part of resurfacing projects. Benefits include the avoided economic and social impacts of fatalities, injuries, and property damage.
The placement of the asphalt wedge during resurfacing operations mitigates the risk posed by edge drop-offs as soon as the paving machine lays down the asphalt mat, allowing the highway agency reasonable time to restore the shoulder or other adjacent graded material.