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Publication Number: FHWA-RD-99-207

Prediction of the Expected Safety Performance of Rural Two-Lane Highways

APPENDIX D

DEFINITIONS OF ROADSIDE HAZARD RATINGS USED WITH THE ACCIDENT PREDICTION ALGORITHM

The accident prediction algorithm uses a roadside hazard rating system developed by Zegeer, et al. to characterize the accident potential for roadside designs found on two-lane highways.(6) Roadside hazard is ranked on a seven-point categorical scale from 1 (best) to 7 (worst). The seven categories of roadside hazard rating are defined as follows:

Rating = 1

  • Wide clear zones greater than or equal to 9 m (30 ft) from the pavement edgeline.
  • Sideslope flatter than 1:4.
  • Recoverable.

Rating = 2

  • Clear zone between 6 and 7.5 m (20 and 25 ft) from pavement edgeline.
  • Sideslope about 1:4.
  • Recoverable.

Rating = 3

  • Clear zone about 3 m (10 ft) from pavement edgeline.
  • Sideslope about 1:3 or 1:4.
  • Rough roadside surface.
  • Marginally recoverable.

Rating = 4

  • Clear zone between 1.5 and 3 m (5 to 10 ft) from pavement edgeline.
  • Sideslope about 1:3 or 1:4.
  • May have guardrail (1.5 to 2 m [5 to 6.5 ft] from pavement edgeline).
  • May have exposed trees, poles, or other objects (about 3 m or 10 ft from pavement edgeline).
  • Marginally forgiving, but increased chance of a reportable roadside collision.

Rating = 5

  • Clear zone between 1.5 and 3 m (5 to 10 ft) from pavement edgeline.
  • Sideslope about 1:3.
  • May have guardrail (0 to 1.5 m [0 to 5 ft] from pavement edgeline).
  • May have rigid obstacles or embankment within 2 to 3 m (6.5 to 10 ft) of pavement edgeline.
  • Virtually non-recoverable.

Rating = 6

  • Clear zone less than or equal to 1.5 m (5 ft).
  • Sideslope about 1:2.
  • No guardrail.
  • Exposed rigid obstacles within 0 to 2 m (0 to 6.5 ft) of the pavement edgeline.
  • Non-recoverable.

Rating = 7

  • Clear zone less than or equal to 1.5 m (5 ft).
  • Sideslope 1:2 or steeper.
  • Cliff or vertical rock cut.
  • No guardrail.
  • Non-recoverable with high likelihood of severe injuries from roadside collision.

     Figures 8 through 14 present photographs illustrating the seven roadside hazard rating categories.

Figure 8. Typical Roadway with Roadside Hazard Rating Equal to 1. Figures 8 through 14 show photographs illustrating the seven roadside hazard rating categories. Roadside Hazard Ratings equal to 1 represent the lowest hazards; Roadside Hazard Ratings equal to 7 represent the greatest hazards. This photograph depicts a two-lane road on flat terrain, running through a grassy area.
Figure 8. Typical Roadway with Roadside Hazard Rating Equal to 1.

Figure 9. Typical Roadway with Roadside Hazard Rating Equal to 2. This picture shows a two-lane road with a clear zone between 6 and 7.5 m (20 and 25 feet) from pavement edgeline, which is recoverable.
Figure 9. Typical Roadway with Roadside Hazard Rating Equal to 2.

Figure 10. Typical Roadway with Roadside Hazard Rating Equal to 3. This picture depicts a two-lane road with a shoulder approximately 5 feet in width and a sideslope about 1:3 or 1:4 with small trees on the roadside.
Figure 10. Typical Roadway with Roadside Hazard Rating Equal to 3.

Figure 11. Typical Roadway with Roadside Hazard Rating Equal to 4. This picture depicts a two-lane road with a horizontal curve bordered by a guardrail fairly close to the edge of pavement.
Figure 11. Typical Roadway with Roadside Hazard Rating Equal to 4.

Figure 12. Typical Roadway with Roadside Hazard Rating Equal to 5. This picture shows a two-lane road with a fairly narrow clear zone sloping into a ditch in which a row of trees is standing.
Figure 12. Typical Roadway with Roadside Hazard Rating Equal to 5.

Figure 13. Typical Roadway with Roadside Hazard Rating Equal to 6. In this picture, a two-lane road winds through a wooded area in which the trees are standing within a few feet of the road.
Figure 13. Typical Roadway with Roadside Hazard Rating Equal to 6.

Figure 14. Typical Roadway with Roadside Hazard Rating Equal to 7. This picture depicts a two-lane road that has been cut through the side of a mountain - boulders directly abut the road on both sides.
Figure 14. Typical Roadway with Roadside Hazard Rating Equal to 7.

 

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