DCAN 15: Vehicular Access Standards
Visibility from the Minor Road
2.1 Good visibility is essential to enable drivers emerging from the minor road to see and be seen by drivers proceeding along the priority road.
Fig 1: Visibility Splays
Visibility is required over the shaded area shown in Figure 1. The xdistance is measured along the centre-line of the minor road from the edge of the running carriageway of the priority road. The y-distance is measured along the near edge of the running carriageway of the priority road from the centre-line of the minor road. Where the access is on the outside of a bend, an additional area will be necessary to provide splays which are tangential to the road edge as shown in Figure 2.
Fig 2: Visibility Splays for Access on Outside of Bend
2.2 The normal requirements for the minor road distance or x-distance are set out in Table A, and the notes thereto. When the minor road is relatively busy and traffic on the priority road is fast, a greater x-distance is required to allow drivers on the priority road to see in good time vehicles approaching the give way or stop line of the minor road. In addition, when the minor road is busy, a greater x-distance is necessary to allow more than one emerging vehicle to accept the same gap in priority road traffic, thus reducing delay and frustration for emerging drivers. If there is a dispute about the predicted minor road traffic volume, it will be determined using a recognised database such as TRICS 3, or failing that by a direct survey of a similar existing development over an acceptable period.
2.3 The normal requirements for the priority road distance or y-distance are set out in Table B and the notes thereto. They depend on the speed of traffic on the priority road, the volume of traffic on both the priority road and the access, and the judgement which the Department makes in any given case about road safety matters.
2.4 In the case of a new access, x- and y- distances must be adjusted as necessary to allow for any planned road improvements. Visibility on the Priority Road