Diagram 642 is used to keep a carriageway clear from obstructions of stopped cars. Used with supplementary plates to show distance and end, but also throughout the route with smaller no stopping signs.
Material: R2/RA2 reflective overlay on aluminium composite backing
7.2.4. The start of the clearway is indicated by a sign to diagram 642 (S3‑2‑4, see Figure 7-1) with a supplementary plate indicating the restricted length in miles; this must be to the nearest whole mile if the distance is greater than three miles (see S18‑3‑4). In order to reduce environmental impact, there is no requirement to provide two signs, one on each side of the road. However, as such clearways generally apply to high‑speed roads, a driver who fails to observe the sign and stops on the main carriageway will be a hazard to other drivers. It is possible that a sign on the nearside of a dual carriageway road might be obscured by a large commercial vehicle and this must be taken into consideration when deciding whether a second sign should be placed on the opposite side of the carriageway. The end of the clearway is indicated by a sign to diagram 642 with an “End” plate as shown in Figure 7-1. Only one sign is required, but a second sign should be considered, particularly where the likelihood of parked vehicles on the road ahead presents a possible hazard; e.g. on a dual carriageway where a single sign on the nearside might be obscured by vehicles in the nearside lane. Where start and end signs are erected on each side of the carriageway, they should be mounted back to back. Traffic authorities should determine whether repeater signs are required and where they are CLEARWAYS 65 placed. However, to ensure that drivers are reminded of the restriction, it is recommended that repeater signs, which may alternate from one side of the carriageway to the other, are placed along the length of the road such that the distance between successive signs is equivalent to a travel time of approximately 60 seconds. As a guide, where the speed limit is 60 mph or more, it is recommended that repeater signs are placed at intervals of approximately 1600 m in each direction. Where the speed limit is 30, 40 or 50 mph, the recommended spacing is 800 m, 1100 m and 1350 m respectively. Where the length of road subject to the prohibition on stopping is less than these distances, in respect of each speed limit (including 60 mph or more), repeater signs are unlikely to be necessary. Where street lighting is provided, it is recommended that repeater signs are mounted on the lighting columns (see Chapter 1).