THE DESIGN OF MOTORWAY ACCESS ROADS

The basic premise of this article is that the design of motorway access ramps should not be limited to ensuring that the sum of the capacity of the entrance ramp and that of the first lane of the motorway should be such that the prescribed level of service of the motorway is not exceeded. It is suggested that the accurate design of acceleration ramps should be based on the avoidance of congestion and accidents on the motorway, the ramp itself, and on the adjacent roads. Design criteria presented here assume that vehicles will maintain a constant speed on the ramp (equal to its design speed), which in any case would not exceed 60-70 km/hr. The length of the acceleration ramp would thus be the product of this speed and the maximum probable waiting time before joining the motorway. /TRRL/