Patent GB-406993-A (GB)
Title: Improvements in road traffic control systems
IPC: G08G1/08
Filed: 1932-09-06
Abstract: 406,993. Road signals for controlling traffic. SIEMENS & GENERAL ELECTRIC RAILWAY SIGNAL CO., Ltd., Tothill Street, and EDWARDS, F. A., 82, Elliscombe Road, Charlton, both in London. Sept. 6, 1932, No. 24846. [Class 118 (ii).] In a system in which impulses from road pads are transmitted to a controller to alter the right of way signals, signals generated by a fast moving vehicle pass at once to the controller whilst those from a slow moving vehicle are delayed. The impulse from the slow moving vehicle is also effective to increase the minimum time during which the right-of-way signal is displayed. Impulses from the road pad pass to the controller via the apparatus shewn in Fig. 2. When a vehicle operates road contacts 11, relay M operates and QM commences to charge. If the vehicle is moving fast the circuit of M is closed for a short period only and MS, which is slow to operate does not charge. When M releases QM discharges through MF, which operates and transmits an impulse over 12 to the controller. Relay MF is energized for a period determined by the charge on QM which charge is inversely proportional to the speed of the vehicle and consequently the duration of the impulse is inversely proportional to the speed of the vehicle. If the vehicle is slow moving M is operated for a period which is long enough for MS to energize. The normal energizing circuit of MF is opened, QM is discharged over the low resistance winding of MS, MSS is energized and a circuit to the controller is completed over 10 to increase the minimum right-of-way period. Relay MS also completes a charging circuit to QMT and a charge builds up in this condenser the value of which is inversely proportional to the speed of the vehicle. When the vehicle leaves the pad, M releases followed by MS and the circuit through NMS is completed, the voltage across NMS depending on the charge on QMT. QMT now discharges through leak ZD so that the voltage across NMS rises and after an interval NMS strikes, QMT charges through MST and MST energises connecting positive to lead 12 to operate the controller. MSS releases and discharges QMT through MST, ensuring the operation of MST for a predetermined time. Should fast moving vehicles cross the pad whilst the timer is operating, their impulses are transmitted at once to the controller ; should slow moving vehicles cross it, MS is re-operated and the delay before the impulse is transmitted is increased. To prevent undue delay in the transmission of the impulse condenser QSS is provided. This condenser charges slowly so long as MSS is operated and should a sufficient time elapse between the operation of MS by two slow moving vehicles, the charge on QSS is such that when QSS and MF are connected, MF operates and transmits a pulse to the controller. As MS is operated whenever a slow moving vehicle crosses the road pad, the right-of-way period is always extended so that if a block of waiting traffic includes a slow moving vehicle, ample time is given, when the right-of-way is transferred, for all vehicles to cross the road. According to the Provisional Specification the increase in the minimum time period is effected by adding resistance to the charging circuit of a condenser, the charging time of which controls the right-of-way period, and the delay in transfer of right-of-way to a slow moving vehicle is effected in the controller, the speed of vehicles being timed by the release of a slow-releasing relay. In this system the amber period is variable depending on whether traffic is or is not on the road from which rightof-way is to be taken and three timers are used to control transfer of right-of-way namely (1) a main timer which is operated when no traffic is on the road having right-of-way and a demand is received from the other road, (2) a gap timer which is used to find a gap in a stream of traffic when vehicles are waiting on the crossroad, and (3) a maximum timer which forcibly takes the right-of-way when required if the traffic stream is continuous. A pedestrianoperated push button is also provided to transfer the right-of-way to allow pedestrians to cross.