Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
153 A P P E N D I X D The following is an excerpt from Prediction of the Expected Safety Performance of Rural Two-Lane Highways (67), describ- ing the distinguishing characteristics of the 7 roadside hazard rating categories. The final set of photos comes from the FHWA IHSDM website. The accident prediction algorithm uses a roadside hazard rating system developed by Zegeer et al. (66) to characterize the accident potential for roadside designs found on two-lane roads. Roadside hazard is ranked on a seven-point categori- cal 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 pave- ment 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. Roadside Hazard Rating Category Descriptions ⢠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 nonrecoverable. 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. ⢠Nonrecoverable with high likelihood of severe injuries from roadside collision. Figures D-1 through D-7 present photographs illustrating the seven roadside hazard rating categories.
154 Figure D-1. Typical roadway with roadside hazard rating equal to 1. Figure D-2. Typical roadway with roadside hazard rating equal to 2. Figure D-3. Typical roadway with roadside hazard rating equal to 3. Figure D-4. Typical roadway with roadside hazard rating equal to 4. Figure D-5. Typical roadway with roadside hazard rating equal to 5. Figure D-6. Typical roadway with roadside hazard rating equal to 6.
155 Figure D-7. Typical roadway with roadside hazard rating equal to 7.
156
157
