Spacings of Unsignalised Intersections in Urban Areas—An Empirical Approach Based on Operational and Safety Requirements

The paper is based on work undertaken for the 2014 edition of the “access management guidelines,” developed for the Western Cape Provincial Government of South Africa, and which will replace the “road access guidelines” published by that Government in 2001. The aspect covered in the paper deals with the spacings that should be allowed between different categories of unsignalised intersections along different categories of urban at-grade roads. Firstly, the paper examines the candidate criteria for determining spacings of unsignalised public roads and private driveways, and then presents the conclusions reached on the appropriate criterion for each combination. The rationale for selecting criteria is based on one of the two presumptions: the task facing the driver negotiating the road and who must undertake processes of decision-making and actions when approaching an intersection ahead (i.e., operational requirements); or alternatively, the manoeuvre required of a driver to avoid a collision (i.e., safety requirements). The application of these principles is used to establish appropriate spacing distances along the through road, depending on the classification of the through road and the type of intersection or driveway intersecting with the through road.