Patent GB-1251188-A (GB)
IPC: G08G1/07
Filed: 1967-12-15
Abstract: 1,251,188. Road signals for controlling traffic. EMI Ltd. 28 Nov., 1968 [15 Dec., 1967], No. 57014/67. Heading G4Q. In a traffic control system for a merge junction C between a first path DL and a second path AB, a plurality of indicators L1 to L20 are arranged in succession along a length of the first path DL and are controlled by detecting means V1 to V20 responsive to movement of a vehicle along the second track AB so as to indicate permitted and prohibited travelling zones for traffic on the first path DL. As shown, normally lamp units L1-L20 show green lamps (G, Fig. 1, not shown) to vehicles travelling along the main road DL. If a coach starts from side road AB from platform 1 the signal lamps L1-L20 are changed sequentially to give a group of five amber and/or red lamps which group moves along the main road to indicate a representation of the position of the coach to drivers on the main road. The spacing of the vehicle detector loops V1-V20 is progressively increased in accordance with the acceleration characteristics of a typical vehicle so that the loops are crossed at a substantially constant rate, e.g. one per second. When the coach passes over the first five detector loops V1-V5 bi-stable circuits (B1-B5, Fig. 1, not shown), are set sequentially to sequentially light the amber lamps in lamp units L1 to L5. When the coach passes the sixth loop V6 this resets bi-stable circuit (B1) to return the unit L1 to a green lamp and sets a bi-stable circuit (B6) to light the amber lamp in unit L6. If the output from loop V6 fails to reset (B1) loops V7 and V8 are also connected to reset (B1) as a safety measure. Similarly, each bistable circuit and lamp unit is reset by the output from the sixth, seventh or eight loop ahead so that a group of five lamps indicating the position of the coach moves along the main road DL. Vehicles on the main road must either keep behind or in front of the group of amber lamps but may overtake this group if rapid braking would be needed to stay behind this group. Near the junction C of the side road with the main road the lamp units L16-L20 have red instead of amber lamps and if any of the group of five lamps is red then the vehicle in the main road must remain behind or in front of the group of lamps. The group of lamps produces a gap in the vehicles on the main road into which it is safe for the coach on the side road acceleration lane to merge. As the merged vehicle crosses vehicle detector loops V21-V24 the main lane lamp units L16- L20 are successively reset to green by bi-stable circuits (B16 to B20). Four detector loops V25-V28 are spaced along the main road and control lamp units L22-L25 visible only to drivers in the acceleration lane to provide an additional safety measure. If there is a slowly moving or stationary vehicle in the main lane approaching the merge point C as it passes detector loops V25-V28 the corresponding lamp units L22-L25 are changed to red to warn a vehicle in the acceleration lane of the danger. The driver in the acceleration lane reduces speed to remain behind the red group of lamps and the drivers in the main lane also reduce their speed due to a corresponding slowing of the moving lamp group in the main lane so that when the merging vehicle does reach the merge point a gap will be present. The lamps L22-L25 are subsequently restored to green by the crossing of the vehicle detector loops V21-V24 in the main road by the main lane vehicle. If the vehicle leaving the platform 1 does not intend to merge but intends to leave via the outlet lane the driver indicates this at the platform to a steering bias detector (SBD, Fig. 16, not shown). The vehicle may be provided with two inductive signalling loops or a pin mounted under the vehicle to follow a slot in the road may be set to the left or right to indicate the outlet lane or main lane is required. The position of the pin could be detected magnetically. When the steering bias detector (SBD) detects a left turn a signal applied via gate (G29) and bi-stable (B29) removes an input from each of gates (G1 to G20) so preventing bi-stables (B1-B20) from being set when a vehicle crosses the vehicle detector loop V1- V20 so that the lamps L1-L20 remain green. The output from gate (G29) also controls gate (G24) and bi-stables (B21, B22) which light a green lamp in a lamp unit L21, located at the departure of the platform, when the turn direction has been detected. When the vehicle passes the first detector loop V1 the lamp unit L21 is reset to red to prevent another vehicle leaving. Once a vehicle has indicated a left turn to the outlet no gap will be provided in the main lane traffic and to warn the driver of this on detecting a left turn indication the bi-stables (B25 to B28) are set so as to switch the lamp units L22-L25 to red. These lamps are restored to green when the vehicle passes over a detector loop V29 in the outlet lane. Restoring of the lamp units L22-L25 to green under these conditions by vehicles in the main lane passing over detectors V21-V24 is prevented by gates (G21-G23). The apparatus described for traffic control of the up-lane UL may be the same as above for the down-lane DL. The lamp units for the up and down lanes may be mounted in a common housing on a crash barrier (Fig. 3, not shown). Means may be provided to detect a fall in the D.C. supply (PS1, Fig. lb, not shown), and switch over to a standby supply (PS2). The lamps are connected to an A.C. supply by lamp drivers which may be triacs. Failure of the supply therefore extinguishes all lamps so that when the lamps are extinguished this warns the drivers that the system is not operating. The Specification directs attention to Specification 1,110,108.