GEOMETRIC ROAD DESIGN-SOME RECENT RESEARCH

The traditional rationale of geometric road design standards is examined and developments and recent research in four aspects of geometric road design are reviewed: the rational basis of design standards; horizontal curve design; sight distance requirements; and the relationship between safety and design. Three main points are brought out in the paper, all of which must be regarded as unproved in the real world and worthy of further consideration. First, the specifications of a design speed, and the adherence to the geometric standards for that speed, does not in itself ensure a safe road. Second, where it is not possible to provide vertical curves with sight distances adequate for overtaking, there may be operational, as well as economic, advantages in designing for minimum sight distance. Third, while higher geometric standards means safer operations for roads designed to 'highway' standard, this may not apply to low standard roads. /TRRL/