Patent GB-494698-A (GB)
Title: Improvements in or relating to traffic control systems
IPC: G08G1/082
Filed: 1937-04-30
Abstract: 494,698. Road signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., PREIST, T. P., and THOMPSON, G. W. April 30, 1937, No. 12405. [Class 118 (ii)] At each intersection in a progressive system the various traffic phases are biassed in turn by signals from a master controller, right of way being granted to the biassed phase as long as it is required but being transferable temporarily to other phases if it is not required by the biassed phase. The biassed phase loses right of way only if a sufficient gap occurs in the traffic and regains it with minimum delay when the traffic restarts. Within the bias period there is provided a hold period which is variable in length and position and during which right of way is forcibly maintained should the progressive plan involve a gap between two displaced streams of traffic The bias period terminates in a check period during which right of way can be transferred only to the next phase in the cycle to be biassed. Right of way may be transferred between unbiassed phases with maximum timing. At a T- junction where a phase is provided to allow turning into the side road, the turning phase follows the main road phase when the latter is biassed, but when the side road phase is biassed right of way reverts directly thereto, and the turning phase may precede the next main road phase. Specification 446,288 is referred to. Master controller not in operation. The three-phase controller, Figs. 2-7, comprises a normal timer FA, A, QA controlled over a resistance 10 for timing the initial and vehicle intervals and the amber period and a maximum timer FB, B, QB controlled over a resistance 11. A quick-stepping circuit is also provided for controlling the magnet S of the sequence cam shaft. When the controller is switched in, the cam shaft advances to the nearest vehicle interval position. Assuming that phase A is given right of way (hereinafter called R.O.W.) and that there is a demand on phase B, relay BR operates over detector DB, locks and connects up BP, ST. The cam-shaft steps quickly through the amber position to position 4 in which BS pulls up and the initial interval is timed. In position 5, ST is disconnected and BR is unlocked, so that phase B keeps R.O.W. and the vehicle interval may be extended by further operation of BR. If there is now a demand on phase C, relay CR connects up CP, ST. The cam shaft is advanced by relay A if a gap occurs in the phase B traffic (BR falls back) or by relay B of the maximum timer and the amber period is timed. In position 7, BP, BS fall back while CS pulls up. If there is a demand on phase B while phase C has R.O.W., the cam-shaft goes in a similar manner to position 1 in which CS falls back and then quickly to position 4 in which BS pulls up. If there are simultaneous demands on phases A, B, the operation of AP cuts out BP and R.O.W. is given to phase A, the demand on phase B being stored by BR. Master controller in operation. The switch S receives 50 impulses per cycle, the first over a synchronizing wire 13 and the remainder over wire 12, and connects up relays W, X, Y over adjustable cross-connections to bias the phases A, B, C in succession. Each relay is connected up shortly before the preceding one is released by short-circuiting to provide a check period. Assuming that phase A is biassed, W, WR are operative and the maximum timer is disabled. If a demand occurs on phase B while phase A has R.O.W., BR connects up ST and R.O.W. is transferred to phase B only if a sufficient gap occurs in the phase A traffic. Relay AR however is adapted to be locked for an adjustable period within the bias period by relay HP to prevent loss of R.O.W. Relay HP is controlled over the switch S by cross-connections which may be varied by manual or time control as required by the progressive plan. R.O.W. may be transferred between the unbiassed phases B, C with maximum timing as above described, but if traffic restarts on phase A, AR connects up AP, STB, ST, PX, so that R.O.W. reverts to that phase after one vehicle interval, since the vehicle extension circuit is opened by STB. The cam shaft steps quickly through phase C, since, even if CR is up, PX prevents operation of CP, CS. In position 1, AS pulls up and STB, PX fall back and the initial interval is timed. Further demands on phase B are stored by BR so that R.O.W. will revert thereto when possible. If traffic restarts on phase A when R.O.W. is about to be transferred from phase B to phase C, i.e. in position 6, CP is up and AP, PX cannot operate and R.O.W. therefore goes to phase C, but is transferred to phase A after one vehicle interval since STB is up. In the case of a similar transfer from phase C to phase B, the cam shaft steps quickly through phase A. During the check period when X is operative as well as W, WR, relay CK is connected up and STB is under control of BR instead of AR. Relay ST cannot be connected up by CR, and therefore phase C cannot obtain R.O.W. until CK relapses at the end of the check period. As shown, phase A keeps R.O.W., but it may be arranged for an all-red condition to be set up. R.O.W. is transferred to phase B, however, in response to a demand provided there is a gap in the phase A traffic by the operation of STB. In this case, PR operates in addition to PX and prevents operation of AP so that R.O.W. cannot revert to phase A during the remainder of the check period. A locking circuit for BR ensures that phase B retains R.O.W. for one vehicle interval beyond the check period. Application to a T-junction, Fig. 8. A turning phase B which has no bias period normally follows a main road phase A, but if the latter phase when unbiassed obtains R.O.W. phase B is either suppressed (Fig. 9) or is placed before phase A (Fig. 10). Relays X, XR, BR are not provided and the circuits are modified as shown in Figs. 9, 10. The lamp indications for the mixed phase AB are given by means of relays RAC, RRC. In both arrangements, when phase A is biassed and has R.O.W., BP is operative in addition to AP, AS. If there is a demand on the side road phase C, a R.O.W. period is given to phase B before the transfer to phase C. This action takes place also when phase A keeps R.O.W. beyond its bias period since BP locks. In Fig. 9, if phase A obtains R.O.W. when it is unbiassed, BP is inoperative and therefore R.O.W. reverts directly to phase C. In Fig. 10, however, a demand on phase A when phase C is biassed connects up BP and R.O.W. is given to phase B by the operation of BS. After one vehicle interval, AP pulls up and R.O.W. goes to phase A, but since AS disconnects BP, R.O.W. then reverts directly to phase C. If there is a demand on phase C while phase B has R.O.W. in front of phase A, CR connects up STB, PX to open the circuit of AP, so that R.O.W. reverts to phase C and the demand on phase A is stored.