Abstract
The purpose of this study is to evaluate the actual highway geometric design properly, and propose a well-balanced design policy especially considering the drivers perception and behavior. In this paper, after classification of all the design elements, the new concept of ‘reversely calculated speed’ as an evaluator of road alignment is introduced and examined. The analysis of the ‘reversely calculated speed’ for actual alignments on Expressways in Japan shows the drivers' perception of physical limitation given by road alignment. Then the actual operating vehicle speed is estimated and analyzed using database of vehicle detectors. Using the five-minutes mean speed, with only one passenger car, observed by detectors in the median lane on more than 7,000 km networks of Expressways in Japan, the speed running absolutely independent can be assumed as an ‘operating speed’ (free speed) reasonably. At last, the values of operating speed are evaluated with highway design elements such as curvature of horizontal radius and vertical grade.
