GB2210719A - Traffic light switching system - Google Patents

Abstract

The invention concerns traffic light control systems. Normally, the traffic-light signal heads at a traffic junction are controlled by a single central controller which contains all the switching necessary to maintain the operation of the traffic light. The switched power is then sent via suitable cabling to the individual traffic light signal heads. The present invention proposes that the actual switching now takes place at individual traffic-light signal heads 11-14 with switching data being telemetered from the control unit 10. The traffic-light signal heads can be linked with the control unit in a ring configuration 15. <IMAGE>

Description

Traffic Light Switching System The present invention concerns, inter alia, the switching of traffic lights.

This results in a large number of individual wires being required between the control cubicle and the multiplicity of traffic signal heads which may exist at any particular Junction, the number of signal heads depending on the road lay-out.

The provision of these multicore cables is relatively expensive and restricts flexibility for changes or extensions to the signalling system.

An object of the present invention is to eliminate the need for a larger number of individual cables between a central control cabinet and signal heads and also to simplify the design of the resulting power switching unit.

Accordingly the present invention provides a traffic light control system comprising a controller unit connected to a plurality of traffic light signal heads, the control unit having means for distributing switching data to the traffic light signal heads and each signal head including power switching units responsive to the switching data sent by the control unit.

In order that the present invention may be more really understood, embodiments thereof will now be described by way 0:, example and with reference to the accompanying drawings, in which, Figure 1 is a simplified diagram of a traffic light control system according to the present invention, Figure 2 is a diagram showing the wiring at a relatively complex junction using standard known techniques, Figure 3 is a diagram of the same junction as Figure 2 using the control system of the present invention, and Figure 4 is a diagram of a control system according to the present invention showing possible enhancements, Referring now to the drawings, Figure 1 shows a traffic light control system comprising a central control unit 10 connected to four sets of traffic lights 11-14 via cabling 15.

The function of control box 10 is to distribute supervisory control information to the lights 11 - 14 and to monitor the operation of signal aspects.

In this arrangement the switching elements for the various lights are removed from the single control unit to each individual signal head or signal pole. Power for the signal aspects is provided from the control unit via a ring system forming part of cabling 15 but is switched to the signal aspects via the control at each head in accordance with a telemetering system running parallel to the power. The effect of this re-arrangement of the control system can best be appreciated from Figure 2 and 3 which shares the same junction. The Circles 20 represent traffic and pedestrian lights controlled by the single control unit 10.

It will be appreciated that the ring system shown in Figure 3, where the power and telemetering are carried in a single multi-core cable 16 is substantially simpler than the older, known system shown in Figure 2. Not only is the amount of cabling substantially reduced but so also is the number of interconnections.

This is an important advantage as the interconnection requirements of cables are becoming more and more critical as safety standards on junctions improve. Each interconnection point is a source of extra cost.

Another disadvantage of the known system illustrated in Figure 2 is that the format of the central control box had to change to accommodate the increasing complexity of the junctions being controlled. This was not because of an increase in size of the electronic control equipment within the box as developments in this field meant that increased complexity could in fact be handled by smaller units of equipment. Rather the increase in size was needed to provide adequate terminations for all the interconnecting cables and to house the multiple switches necessary for multi-phase control.

The basic system shown in Figure 1 establishes a ring format in which power andKtelemetering data are transmitted around the lights being controlled. Once this arrangment has been established it is possible to add further functions to the control system. One such function could be detection of ambient conditions such as the presence of ice or fog. Detection of such conditions could then be used to set off appropriate warnings. Additionally one or more of the roads, could have associated traffic counters or devices for weighing and classifying passing traffic. In such a case the control unit 10 could be in communication with a central control where data from a large number of control units could be correlated and acted upon.Such an enhanced system is shown in Figure 4 of the drawings where ice and fog detectors are shown at 30 and 31 respectively, a weighing and clastification device at 32, and a traffic counter at 33. Other detectors are generally indicated at 34. One function these detectors can carry out will be discussed later.

Whatever the nature of the control system the power cabling and control circuitry can take a number of different forms such as a ring configuration, a radial or star configuration or any combination of these two circuit topographies.

It will also be appreciated that the power supply for feeding the signal heads though usually a mains voltage can also be at a reduced voltage or even a DC supply.

It will also be appreciated that the basic configuration described with each signal head having its own power switching element enables the use of relatively simple, standardised power switching elements. This is because each power switching element has only to provide a maximum current equivalent to the number of lamps actually in or directly connected to the signal head. In virtually all cases this number will be one or two.

In modern microprocessor controlled controllers deploying solid state power switches it is required in the UK and custom and practise in many overseas countries for the status of certain lamps within the traffic light assembly to be monitored.

Typically two forms of monitoring are used. One form is applied to green lamps so that the voltage existing across each green lamp is monitored. External hardware and logic within the processor system then independently monitor the voltages applied to all green lamps within the controlled junction complex to ensure that "conflicting greens" (i.e. a dangerous condition when if motorists simultaneously obey the invitation to proceed as signalled by green lamps they will have an accident within the controlled and therefore theoretically protected environs of the junction) cause an immediate shut down of the control system should a conflict occur.

Other situations require the current being taken by say the red lamp to be monitored to confirm that the lamp has actually come on. In the event of a red lamp being unavailable certain adjustments are made to the controller timings and sequences and in the event of several defined red lamps being unavailable the junction controller will be shut down.

In the embodiments just described it is advantageous for these types of lamp monitoring function to be carried out, at least at the detection level, within the distributed switching system contained within the traffic light signal head.

Providing distributed power switching adds to the complexity of the monitoring sub-function since the information on all the individual lamp statuses relevant to a particular decision must be simultaneously available to all elements involved in that decision. For example for a green conflict monitoring, it is necessary for some part of the system to know exactly which lamps constitute a green conflict. The monitoring function must then provide the system with information on which of these lamps are on at any one time. This information may be held within the central processor system of the main logic equipment but the present invention does not preclude the possibility of distributed intelligence within the lamp switching assemblies whereby at configuration they are given data sufficient to enable some local group voting system for example to make the decision.

The present invention also recognises the possibility of the lamp switching module monitoring the status of the lamp filaments under all conditions, rather than inferring their condition from voltage and current measurements when the lamp is on.

Data representing the lamp or filament statuses will obviously be sent back to the control cubicle over similar communication circuits to those already described to remotely control the remote power switches.

However, the present invention does not preclude the possibility of distributed decision intelligence within the lamp switching assemblies to enable them to perform all, or part, of the detection of and responses to, undersirable conditions.

Claims (4)

1. A traffic light control system comprising a controller unit connected to a plurality of traffic light signal heads, the control unit having means for distributing switching data to the traffic light signal heads and each signal head including power switching units responsive to the switching data sent by the control unit.

2. A system as claimed in Claim 1, wherein the control unit and the traffic light signal heads are connected in a continuous ring for the transmission of the switching data.

3. A system as claimed in Claim 2 wherein in operation of the system power for the signal heads is transmitted in parallel with the switching data.

4. A system as claimed in any one of the preceding claims and including one or more detection devices connected to the control unit.