The principal aim of the project was to study the advantages and disadvantages of wedge and parallel exits to vehicular traffic in the light of traffic and accident studies. To this end the traffic studies were focussed on the course described by the turning off manoeuvre, and speeds prior to and along the exit. The accident studies were focussed on the differences in road safety between wedge and parallel exits and included an investigation of the road safety of exits in relation to access roads. The results of these studies suggest that drivers make considerable use of the advantages of parallel exits. They also suggest that motorway traffic is liable to be disrupted by vehicles turning off into certain wedge exits. The average accident risk attached to exits with parallel lanes does not appear to be definitely lower. However there is a high accident risk attached to the ramp compared with other parts of the exit zone. The proportion of accidents in the exit zone is larger than in the access zone.
Abstract