EVALUATION OF HIGHWAY GEOMETRIC DESIGN ANDANALYSIS OF ACTUAL OPERATING SPEED

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

Keywords:

highway geometric design , operating speed , drivers' perception and behavior