Overtaking design sight distances for rural road design

Overtaking sight distances presently used in two way two lane rural road design are based on research of the early 1940's. Since that period vehicle performances have changed and these design sight distances need to be revised. In this paper the author outlines the derivation and use of overtaking sight distances based on the experimental results of a recent overtaking study conducted at the Australian Road Research Board (ARRB). The derived design overtaking sight distances have two requirements. First, the sight distance must be greater than 'the establishment sight distance' so that most drivers would initiate an overtaking manoeuvre. These establishment sight distances range from 350 m at a design speed of 50 km/h to 1690 m at 130 km/h. Second, once a driver has initiated an overtaking manoeuvre he must have sufficient sight distance to be able to continue and to complete the manoeuvre with safety. These sight distances were termed continuation sight distances and ranged from 165 m at a design speed of 50 km/h to 820 m at 130 km/h. The proposed sight distances are larger than those presently used but, when used with new road design approaches (eg, rahmann 1979), the resultant road design is similar to that obtained using present methods.