Alternative methods of intersection control

Highway authority engineers frequently face the problem of what type of control to adopt at a particular intersection or junction. In the past, unless there was an unusual geometric consideration, priority rule control was generally replaced by traffic signals when the published warrants for signal installation were met. Recently, the design criteria for the installation of a roundabout have been modified so that a roundabout can usually be fitted within the existing road boundaries. On the other hand, there are no comparable warrants for roundabouts. This paper examines the existing traffic signal warrants which are primarily to reduce delay and as a consequence hazard and accidents. The total intersection delay and hence road user cost for various standard flows of vehicles and pedestrians is calculated theoretically. This cost can be compared with the theoretical cost for the same flows under priority rule control. Next the same flows are assumed to pass through a roundabout and the cost is again calculated. From all the calculations, it is shown that either priority rule control should be retained or roundabouts should be installed in many more locations unless there are special circumstances requiring traffic signals. Criteria are proposed. The calculations can be performed very rapidly with ordinary computing equipment (a).