The Safety Edge

Downloadable Version
PDF [2.6 MB]

The Safety Edge Pavement Edge Treatment

You Can Reduce Pavement Edge Drop-off Hazards

Photo of a man measuring the angle and depth of a pavement edge dropoff. Source: FHWA

Saves Lives
Reduces Tort Liability
Reduces Maintenance Expense
Costs Less than 1 Percent of Pavement Resurfacing Budget

Logo: Safe Roads for a Safer Future – Investment in roadway safety saves lives.

Pavement Edges Can Pose Serious Safety Hazards

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-off-road 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.1

How Hazardous 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

Photograph shows a person's shoe and leg on the unpaved shoulder next to the pavement dropoff, illustrating the depth of the dropoff from the top of the asphalt to the unpaved surface. Photo source: FHWA.
Sharp, steep pavement edge drop-offs can
contribute to crashes.

When a driver drifts onto the roadway shoulder and tries to steer back onto the pavement, the vertical pavement edge can create a "tire scrubbing" condition that may result in over-steering. If drivers over-steer to return to the roadway without reducing speed, they are prone 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.

Illustration of a vehicle drifting over onto the shoulder, falling off the edge, and then overcompensating to return to the roadway and causing a crash. Text reads: This is a typical diagram for a crash caused by tire scrubbing. The vehicle at left scrubbed the edge of the pavement, and when it returned, the driver overcorrected, lost control, crossed into the adjacent lane, and struck an oncoming vehicle. Graphic source: AAA Foundation for Highway Safety.

Text box reads: 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.

Diagram shows cutaway of roadway. Atop the existing base or pavement is a new asphalt overlay surface. The edge of the new asphalt overlay does not drop off, but is cut into a wedge shape at a 30° to 35° angle. Graphic source: J. Pitzer.

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.

Relative Safety of Various Edge Elevations and Shapes

The chart below shows how various edge shapes relate to safety at speeds of up to 55 mph.

Chart shows how safety decreases as the longitudinal edge elevation (in inches) increases. Graphic Source: Zimmer and Ivey, Texas Transportation Institute.

Photograph of a safety wedge shoe. The text below the image reads: 'The Safety Wedge Shoe is a special edging device that asphalt paving contractors can install on new or existing resurfacing equipment to shape the Safety Edge.' Photo source: FHWA

Contact the FHWA for More Information about the Safety Edge and other Roadway Departure Crash Countermeasures

For more information about Roadway Departure issues and effective countermeasures to prevent Roadway Departure crashes, go to the FHWA Office of Safety's Web site at http://safety.fhwa.dot.gov/ and click on "Road Departure." FHWA contacts for technical assistance with the Safety Edge are listed below.

Contacts

Frank JulianFHWA Resource Center
Safety and Design Team
(404) 562-3689
Frank.Julian@dot.gov

Chris Wagner
FHWA Resource Center
Pavement and Materials Team
(404) 562-3693
Christopher.Wagner@dot.gov

Cathy Satterfield
FHWA Office of Safety
Roadway Departure Team
(708) 283-3552
Cathy.Satterfield@dot.gov

__________________________

1 Hallmark et. al: Safety Impacts of Pavement Edge Drop-Offs, AAA Foundation for Highway Safety, Washington, DC, September 2006.

FHWA logo.

Publication Number FHWA-SA-09-023

Program Contact

Cathy Satterfield

708-283-3552

Publications

Low Cost Treatments for Horizontal Curve Safety

Pavement Edge Brochure: The Safety Edge