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

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

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.

Figure 9. Typical Roadway with Roadside Hazard Rating Equal to 2.

Figure 10. Typical Roadway with Roadside Hazard Rating Equal to 3.

Figure 11. Typical Roadway with Roadside Hazard Rating Equal to 4.

Figure 12. Typical Roadway with Roadside Hazard Rating Equal to 5.

Figure 13. Typical Roadway with Roadside Hazard Rating Equal to 6.

Figure 14. Typical Roadway with Roadside Hazard Rating Equal to 7.

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