245. Two types of traffic light signals are at present prescribed in Regulations. They are the red, amber and green signals (or red and green only) used primarily to control traffic at road junctions and road works and the twin horizontally mounted red flashing lights used mainly at railway level crossings.
The red, amber and green signals used in this country are to a greater degree vehicle actuated (as distinct from fixed time) than is the case elsewhere in the world . We warmly approve the policy of using vehicle actuated signals, for it means that their operation can be made as sensitive as possible to variations of vehicle flow. This minimises delay and reduces accident risks by arranging that signal changes occur whenever possible during gaps in traffic flow. We recommend that the replacement of fixed time by vehicle actuated signals should continue until no fixed time installations remain. Changes in vehicle flow on all-purpose roads will call for continual adjustments to the timing of lights and we strongly advocate the use by local authorities of specialist staff for the servicing, adjustment and maintenance of their traffic signals. This should include routine checking of the optical equipment to ensure that intensities do not fall below the required standard, as is too often the case today.
246. We think that the main direction in which improvement of traffic signals can be obtained is in the wider use of selective control of complicated junctions by green arrows. Left and right pointing green arrows are already prescribed in Regulations but we recommend that further latitude be given by permission to use arrows pointing in any direction above the horizontal. There are, however, limits to the replacement of a full green signal by green arrows. For instance, where there are more than four arms to a junction it would not be physically possible to use only green arrows unless a double arrow were used on a single lens-which we do not advocate owing to its lack of clarity. A single filter arrow followed by a full green signal would be preferable. As a general rule therefore the full green signal should be used to indicate that movement in all directions is possible ; this indication should not be attempted by arrows alone. Where a green filter arrow is in operation so that, for example, traffic may turn to the left while the forward stream is still held by a red light, a greater use should be made of advance signs (figure 133) and carriageway markings (see paragraph 235) to help drivers to move early enough into the appropriate lane. There is otherwise a risk that the advantage of the filter lane is lost because it becomes blocked by a driver not intending to go in that direction.
247. Where there is a heavy right-turn movement, this traffic is sometimes helped by giving a red signal to traffic approaching on the other side of the junction before the signal on the side with the heavy right-turn movement is changed from green to red (a device known as 'early cut-off period'). Where this facility is provided a right-pointing green arrow is displayed in addition to the green signal during the latter portion of the green signal while traffic in the opposite direction is stopped. We endorse the action of the Departments in recommending general use of this arrangement where early cut-off periods are provided.
248. Where signals have to be installed on high-speed roads there is a need for them to be more conspicuous and visible from a greater distance than would
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