Roadside safety improvement programs on freeways : a cost-effectiveness priority approach.

A cost effectiveness approach for programming roadside safety improvements is developed. To evaluate the effectiveness of roadside safety improvements, a probabilistic hazard index model was developed. This model considers: 1) vehicular roadside encroachment frequencies; 2) the percentile distribution for the lateral displacement of encroaching vehicles; 3) the lateral placement of the roadside obstacle; 4) the size of the obstacle and 5) the accident severity associated with the obstacle.