Utility Poles: Appendix 5
Roadside adjustment factors for increasing pole offset
Due to the presence of other roadside objects, when applying a countermeasure such as increasing the pole offset, the net reduction in accidents is expected to be less than the reduction in utility pole accidents. For example, "assume a line of utility poles at 5-foot lateral offset and a dense row of trees at a 6-foot offset behind the poles. The roadside adjustment for moving only the utility poles back to 30 feet would be nearly zero, since virtually all of the reduction in utility pole accidents would be negated by an increase in vehicle-tree accidents" (Zegeer and Cynecki, 1984).
The roadside adjustment factor developed by Zegeer and Cynecki (1984) and shown in Table 1, was based on a complex procedure that involved "computing the probability of run-off-road accidents and utility pole accidents before and after a countermeasure". To use the roadside adjustment factors shown in Table 1, the percent coverage of fixed-objects must be determined for a given roadway section based on the procedure developed by Graham and Harwood (1982), which involves counting rigid fixed-objects in 200-foot increments along the roadway back to specified increments of lateral offset. Zegeer and Cynecki (1984) provide a list of fixed objects to be counted (and not counted). In order to determine the expected reduction in accidents as a result of an increase in the pole offset, the crash reduction factors shown in Exhibit 9A of the guide have to be multiplied by the corresponding roadside adjustment factor from Table 1, to obtain a revised estimate of the expected reduction in crashes due to the increase in the pole offset.
Table 1: Roadside adjustment factors for increasing pole offset
Source: Zegeer and Cynecki (1984)