VALIDATION OF THE 10 MPH RULE IN HIGHWAY DESIGN CONSISTENCY PROCEDURE

The main purpose of this study was to validate, for use in Korea, the 10 mph rule, a design criterion used to check the appropriateness of highway alignment design. For this, a new speed prediction model was developed. The model has the capability of reflecting the effect of the driver's available sight distance into vehicle running speeds. By the speed prediction model, vehicle running speeds were calculated for horizontal alignments, vertical alignments, and combinations of horizontal and vertical alignments. The main concept in the speed prediction model was that drivers would travel with the speed determined by the available sight distance provided at each highway segment. Field surveys were made and the predicted speeds seemed to be in a good agreement. In addition, it was found that the larger the speed change involved, the higher the accident rates. It is believed that the new method is useful to evaluate the safety and the design consistency of a highway.