Page:Report of the Departmental Committee on Traffic Signs (1946).djvu/61

 changes. We desire, however, to emphasise that traffic signals should be installed only where it is not practicable by improved road layout (e.g. by grade separation or by roundabouts) to provide for the safe and uninterrupted flow of traffic.

Signal sequence

168. The signal sequence Red, Red with Amber, Green, Amber, is standard in this country on all permanent installations at road junctions. The tendency for traffic to start immediately the Red with Amber signal is shown constitutes a possible source of danger and for that reason it has been suggested that the Red with Amber signal should be omitted from the standard sequence. We feel that the matter merits investigation and recommend that a selected group of signals should be operated with the Red with Amber omitted, the period of the Red signal being extended to include the period previously covered by the Red with Amber. The Amber signal following the Green would not be altered. A proposed experiment on these lines was, we understand, postponed by the outbreak of war, and the shortage of skilled labour to make necessary alterations in the apparatus has so far prevented the carrying out of the experiment.

As the result of experience the Department has standardised the length of the Amber period at 3 seconds. Where a longer clearing interval is required to avoid conflict between opposing traffic streams at a junction this is done by the provision of an all-Red period. We endorse this policy.

Use of Green Arrow

169. The 1933 Committee recommended the use of a Green Arrow signal to be shown in conjunction with the Red signal to indicate that drivers of vehicles intending to proceed in a particular direction (e.g. to turn left) may do so notwithstanding that the Red signal is displayed. This filtration of vehicular traffic may not be in the best interests of pedestrian safety and it has therefore been the practice of the Department to restrict this use of the Green Arrow to cases where it is not otherwise possible to effect satisfactory clearance through the junction: We endorse this policy.

A further use which is now made of the Green Arrow is to substitute it for the normal Green signal where all the traffic passing the signal must turn left. We recommend the continuance of this practice.

The Green Arrow signal consists of a green arrow on a black ground, the area of the green illuminated arrow being about 30 per cent of the illuminated area of the standard 8 in. signal. It has at times been suggested that greater conspicuity would be obtained if the colour arrangements were reversed to show a black arrow on a green ground. We do not recommend any change, since it seems to us that the green arrow on the black ground better suggests that a left turn is the only movement permitted, and we have no evidence that in its present form it is not sufficiently conspicuous.

Size of lens

170. We do not recommend any change in the existing standard size of signal lens of 8 in. diameter.

Flexible progressive system

171. In the method of control known as the flexible progressive system the signals at a number of adjacent junctions can be co-ordinated in such a way that traffic may proceed at a uniform speed along the main thoroughfare without being held up at each successive intersection, while at the same time frequent opportunities are given for cross traffic to proceed. A number of installations of this type have given satisfactory results.