GB803916A - Improvements in or relating to traffic control systems - Google Patents

Abstract

803,916. Road signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Dec. 3, 1956 [Dec. 9, 1955], No. 35334/55. Drawings to Specification. Class 118 (2). In a traffic signalling system arranged so that an extension of right-of-way is given to a vehicle approaching an intersection on a traffic lane already possessing right-of-way but that right-of-way is terminated after it has been given for a maximum period if it is required by another lane, and arranged so that the warning or amber signals on the two conflicting lanes are of fixed duration but capable of displacement in order to give a suitable clearance period, arrangements are provided whereby, if withdrawal of right-of-way is effected due to expiry of the maximum period, the amber displacement period is automatically increased or an amber displacement is introduced if the amber periods are normally concurrent, so as to give adequate clearance for the vehicle which is losing right-ofway. The facility provided by the invention is particularly necessary where a vehicle loses right-of-way on a maximum change immediately it has passed the road detector. Two arrangements are described. In the first, Fig. 1 (not shown), a fixed increase is made in the amber displacement. The system includes a timer circuit for the amber displacement utilizing the discharge of a capacitor to time the displacement and the arrangement operates to increase the resistance of the discharge path when a change takes place on maximum. In the second, Fig. 2 (not shown), the clearance period is variable depending on traffic conditions. The system again includes a timer for the amber displacement, but when a change takes place on maximum, although amber is displayed to the lane losing right-of-way, the start of the displacement timer is delayed until the full extension period applicable to the last vehicle to pass the road detector has expired. The effective displacement is thus increased and a vehicle always receives a clearance period equal to the sum of the whole of the extension period and the amber displacement period. It is stated that the amber displacement may be such that the two amber periods do not overlap and are separated by an all-red period. The normal amber displacement, i.e. for changes other than at maximum, may be reduced, possibly even to zero. Specification 725,475 is referred to.