be possible with the normal installation at the roadside . This is particularly so on 3-lane dual-carriageways where drivers on the centre lane may have their view of the signal obscured by vehicles in the other lanes. It is also necessary on wide and heavily trafficked roads in urban areas. In both these circumstances we think that overhead traffic signals, as already used abroad, may be necessary. If so, these should be suspended where possible from existing structures or the walls of buildings. But where special gantries are unavoidable they should be designed with due regard to amenity.
Overhead signals could also be used to control tidal flows by lane switching, a green vertical arrow indicating that movement is permitted and a red cross that it is not. Experience abroad suggests that these lane control signals should be repeated at intervals of not more than 300 yards and that they should not be placed where they can be confused with signals controlling intersections.
249. There is a serious danger that traffic signals in urban areas may fail to be seen because they become confused with the background lights of shops and advertisements. Powers already exist to prevent such lights being placed where they conflict seriously with the efficiency of traffic signals. We recommend that highway authorities make a more constant review of distracting lights placed in the line of traffic signals and take such steps as are possible to have them removed. Some amelioration can, however, be achieved by the use of backing boards for traffic lights. The claims of both black and yellow have been advanced for these boards but we think black makes the more effective contrast for light signals. The backing board can be made more conspicuous by providing a white or coloured border.
We believe that the visibility of traffic signals would be further enhanced by contrast if the signal heads were painted entirely black, instead of being banded black and white as they are at present. As it is important that traffic signal installations should be conspicuous both to drivers and pedestrians we consider that the present practice of having black and white bands on the supporting posts should be continued. If, as we advocate, further consideration is given to improving the general design of light signals the addition of backing boards should be taken into account as part of the design problem.
250. We regard the twin red flashing light signal as being satisfactory for the purposes for which it is used and recommend no change.
251. It remains to consider the problems of how best to help pedestrians at traffic signals. This help will normally be at the expense of vehicle flow, as is the case with the all-red phase when introduced for pedestrian benefit at junctions, and a decision on whether to introduce it will depend upon the number of pedestrians to be catered for and the vehicle flow. Combined vehicle and pedestrian phases are sometimes possible where the only permitted movements during the vehicle phase do not pass over the pedestrian crossing. We think that the decision to provide such arrangements must be a matter for the experienced judgment of the Departments and that no rule of thumb can be formulated. Nevertheless we feel that the growth of traffic in urban areas makes it necessary to give pedestrians more help in crossing the road safely.
When a pedestrian phase is provided indications are given to pedestrians by special signals advising them to cross or wait. This phase is usually called by
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