GB2610157A - Traffic Signal Controller System - Google Patents

Abstract

A traffic light controller (20, Figure 1) for controlling multiple traffic light units has multiple operating modes, each corresponding to a particular sequencing or timing arrangement (e.g. a fixed timing sequence mode, a manual mode and a vehicle-activated mode). The controller can accept demands (i.e. requests for a traffic light to adopt a particular state) and service them according to the operating mode. It can save in memory any un-serviced demands preceding a mode change and prioritise them following the mode change. This can reduce the waiting time for a vehicle following the mode change. The demands may be manual (i.e. from the controller), natural (i.e. from a vehicle sensor) or forced or nudge demands from an internal timer. The controller may receive a demand, add it to a demand queue in a priority-based position, service the demands according to their priorities, remove serviced demands from the queue and maintain the demand queue across mode switches.

Description

Traffic Signal Controller System The present invention relates to traffic control systems, such as traffic light systems. It more particularly relates to portable traffic control systems that are used on a temporary basis, such as at roadworks etc. It is commonplace to encounter portable traffic lights when travelling on the roads in the UK and elsewhere. These traffic lights have the usual red, yellow (or amber) and green lights that signal to a driver to stop, prepare to go, or to go, as is commonly understood. They are typically used where workers are conducting activities on or near to roads, partially blocking a road, or where the permanent traffic lights have been turned off for servicing etc. (collectively termed herein a blockage). Where the aforementioned blockages prevent the traffic from flowing safely in the normal manner it is expected that traffic volumes will be compromised. There are various configurations of lights that may be used, dependent upon the complexity of the road junctions in the vicinity of the portable traffic lights. If the portable CO traffic lights are placed, for example, on a road with no side roads or other junctions in the vicinity thereof, then typically there will be a minimum of one unit placed at each end of the blockage etc., and so comprise of a group having a minimum of two units present on site. These are known as two-phase systems.

If there is a junction, such as a side-road that needs traffic therefrom to be controlled also, then the group will have a minimum of three units, and it may be referred to as a three-phase system. Similarly, four-phase systems, comprising a group of four or more units may be used where there is an additional traffic path that needs to be controlled, and so on. It will be appreciated that sometimes multiple units may be used at a single approach, such as at one end of a blockage, e.g., where there is a wide road or multiple lane carriageway, where a unit may be used either side of the road. In such cases, the units will be synchronised to work together, and will effectively be a single phase (i.e. showing the same lights at the same time) for the purposes of this application.

Portable traffic control systems such as those described above have sequencing timings that determine how long each traffic light unit is to remain in a particular state (e.g. red or green). As such, a group of portable traffic lights that are controlling vehicular access around a blockage etc. will be in communication with each other via a radio link, so that they remain correctly synchronized (e.g. where the timings of the changes from red to green on one unit correctly synchronize to the corresponding changes in another light of the group). The sequencing timings may be fixed, whereby the timing for each state is not changeable. More commonly however, the timings may be varied. For example, a portable traffic light unit may have a vehicle detector, such as a radar system, to detect the approach of a vehicle towards the unit. A control system common to the group of portable traffic lights controls the sequencing (as well as other aspects) of the group of lights. If the control system is notified by a radar on one traffic light unit (which is, say, currently at red) of the arrival of a vehicle at the traffic light unit, it may adjust the relative timing of the lights within the group to bring that traffic light to green earlier than it otherwise would without the notification. The effect is generally to increase the traffic flow around the blockage. The notification by the vehicle detector to the control system is one type of "demand", where a demand is a signal sent to the control system advising of the need to set a particular unit to green.

Demand types may, for example, comprise of: a) a manual demand, where the demand is placed by a human operator; b) a natural demand, where the demand is place by a vehicle sensor, or by a pedestrian CO controller (e.g. to enable a pedestrian to cross); c) a forced demand, sometimes referred to as a permanent demand, which is a demand placed automatically by the control system; to ensure that the aforementioned fixed time operation is provided for and such sequentially rotates the lights through the operational 20 groups.

d) a nudge demand, which is a demand issued where there has been a period of inactivity (such as a unit remaining on red) for a pre-set duration.

The demands may be made by individual traffic light units within the group., or by a human operator etc., directed to one or more traffic light units.

Modern portable traffic systems often have multiple modes, and are switchable therebetween, where a mode is a given timing sequence or control method. For example, different modes may comprise: a) a fixed timing sequence mode, where the duration of red and green lights on a given unit is fixed; b) a manual mode, where the units within a group of traffic light units are controlled by a human operator; c) a Vehicle Activated (VA) mode, where the duration of red and green lights on a given unit is varied according to demands place by vehicle sensors (such as is explained above in relation to a radar sensor); d) an All-Red mode, where all operational units are set to red.

It is often the case that the operational mode of the group needs to be changed. For example, an operator may switch the group from a fixed timing mode to a manual mode to facilitate some plant manoeuvres etc., and then switch to a VA mode. These mode changes can on occasion leave vehicles waiting at a red light for long periods, leading to driver frustration, wasted time, and traffic jams.

Embodiments of the invention have the object of addressing one or more of the above

shortcomings of the background art.

According to a first aspect of the invention there is provided a portable traffic light controller comprising a computer system arranged to have at least two inputs from respective traffic light units, and at least two outputs to the respective traffic light units, wherein the computer CO system comprises of a processor and memory, and wherein the control system is arranged to control lights on the at least one traffic light unit, to indicate to traffic and/or pedestrians whether to go or to stop, and further wherein it has a plurality of operating modes and facility for changing therebetween, each mode corresponding to a particular sequencing or timing arrangement for the at least two traffic light units, and further wherein the system is able to accept demands, where a demand is a request for one or more traffic light units to go to a particular state, and to service the demands by sending signals to one or more of the outputs to put the corresponding traffic light unit(s) into the particular state according to the sequencing or timing arrangement of the current mode, wherein the system is further arranged to save in memory any unserviced demands immediately preceding a mode change and to prioritise the unserviced demands following the mode change.

Thus, embodiments of the invention provide the advantage that following a mode change the demands previously received may be serviced, preventing unnecessary delays to vehicles and/or pedestrians. Such delays can become excessive in prior art systems, where the prior demands are lost, leading to frustration among drivers or pedestrians, and an increased likelihood of inducing bad behaviour among drivers, such as by ignoring a red light.

Note that an unserviced demand is a demand (such as those mentioned herein -a waiting vehicle or pedestrian, or a request from a manual controller to set a unit to red, etc.) from or pertaining to a unit, where the controller has not yet put that unit into a state as requested by the demand (to turn the relevant unit to green). A serviced demand is a demand that has been satisfied by setting the relevant unit to the demanded state.

Advantageously, in some embodiments the controller has inputs for receiving signals from at least one vehicle sensor or other external environmental sensor or input (including a pedestrian push-button switch) for detecting the presence of waiting vehicles/pedestrians, and for receiving signals from at least one manual controller; and wherein the controller is arranged to regard signals so received as demands.

The manual controller may be a controller operated by a person having responsibility for the traffic light group, such as an engineer etc. The vehicle sensor may be for example a radar unit arranged to detect approaching traffic, and the pedestrian push-button may be a button located on, or in the vicinity of the traffic light unit, and arranged to be pressed by pedestrians wishing to cross the road.

CO

In some embodiments the controller is adapted to respond to demands placed by: a) an input from the manual controller(s), known as a "manual" demand; b) an input from the at least one vehicle sensor, or other external environmental CCI sensor, knows as a "natural" demand; c) an internal timer according to sequence and timing settings of a current operating mode, known as a "forced" demand; and d) an internal watchdog timer, acting as a "nudge" demand.

Other embodiments may be adapted to additional, or different demands.

In some embodiments, the traffic light controller is arranged to have modes that comprise at least: i) a fixed timing sequence mode; fi) a manual mode; and iii) a vehicle activated ("VA") mode; Advantageously, a pedestrian activated mode may also be present in some embodiments. Also, some embodiments may have an all-red mode, where all units are arranged to stop the flow of traffic.

In some embodiments the controller is adapted to prioritise demands according to a prioritisation hierarchy having the order a) to d) as mentioned above (highest priority to lowest), and to service any simultaneous demands according to the hierarchy.

Other embodiments may use a prioritisation hierarchy different to the above.

Thus, a demand queue may be formed, comprising the demands that remain currently unserviced, and with new demands joining their place in the queue according to their particular prioritisation. For example, if the demand queue currently comprises a series of demands, and a higher priority demand occurs, then that higher priority demand will "jump the queue" according to the relative priorities of it and the existing demands.

In some embodiments the controller may be arranged such that following a mode change, any demands that occurred prior to the mode change, and which remain unserviced are serviced according to the hierarchy, and wherein any demands that occur after the mode CO change but before any such prior demands are serviced, are themselves serviced according to the same hierarchy.

Thus, the demand queue operates in similar fashion as if the mode changed did not occur, until the demands have been serviced.

According to a second aspect of the present invention there is provided a traffic control system comprising a traffic light controller as described above, and at least two traffic light units.

The system may further comprise means for communicating between the traffic light units and the traffic light controller. The means for communicating may comprise at least one of a radio link, or a data cable.

In some embodiments the traffic light controller may be located within a portable traffic light unit. In some embodiments each unit may have located therein a traffic light controller, wherein, when the units are in use in a group, one of the traffic light controllers is designated as a master controller, and dictates to the other units within a group the operation of the lights on the unit.

Advantageously, in some embodiments each unit has located thereon, or connected thereto, a vehicle sensor for detecting the presence of vehicles and/or a manual push-button for indicating the presence of pedestrians. In some embodiments some of the units may be fitted with both a vehicle sensor, and push-switch for pedestrians to indicate their presence, and desire to cross a road, and some units will be fitted with just a vehicle sensor. In some embodiments only some of the units will be fitted with sensors, whilst others may have no sensors or push-switches at all.

Advantageously, in some embodiments, the system is arranged to treat a signal from a vehicle sensor or manual push-button from a pedestrian controller as a demand. Further, in some embodiments, the system is arranged to treat a signal from the manual controller as a demand, where the manual controller is a controller is operated by a human operator of the traffic light group.

According to a further embodiment of the present invention there is provided a method for CO controlling a plurality of traffic light units, wherein the traffic light units are arranged to be operative in a plurality of different modes of operation, comprising at least a fixed timing mode, a vehicle actuated mode, and a manually controlled mode, where the mode of operation may be switched whilst the units are operative, and wherein the units are responsive to demands, where a demand is a request for one or more traffic light units to go to a particular state, and to service the demands by sending signals to one or more of the outputs to put the corresponding traffic light unit(s) into the particular state according to a sequencing or timing arrangement of the current mode, the method comprising the steps of: a) receiving the demand; b) adding the demand to a demand queue in a position according to an assigned priority of the demand; c) servicing the demands according to their priority within the demand queue; d) removing serviced demands from the demand queue; 30 wherein the demand queue is maintained across mode switches.

The method may advantageously be implemented on a microprocessor or microcontroller, with appropriate memory in communication therewith, as would be apparent to the normally skilled person. It may also be implemented in any other suitable manner, such as with hardware logic devices, or a Field Programmable Gate Array (FPGA).

According to a further aspect of the present invention there is provided a computer program product comprising instructions to cause the traffic light controller as described herein to implement the above method.

Embodiments of the invention are further described hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows in functional form a unit of the present invention, comprising a traffic light head, control electronic, and a battery power pack; Figure 2 shows a flow chart of the operation of an embodiment of the invention; Figure 3 shows an example of operation of an embodiment of the present invention at a 4-way traffic junction, and its response to demands, as compared to prior art operation; and CO Figure 4 shows a further example of operation of an embodiment of the present invention at a 4-way traffic junction, as compared to prior art operation, but with a high priority demand being placed.

CD 20 It is preferable when installing traffic light systems to have a sequencing system that ideally O will, on average, produce an efficient traffic flow. This is true for fixed (i.e. permanent) traffic light installations, where significant effort is typically spent in the planning process to achieve this. It is also true for temporary traffic light systems as described herein. However, from the nature of such temporary traffic light installations, the amount of time that can go into planning a sequencing arrangement is much less than with permanent fixtures. However, it is commonplace for temporary traffic light systems to have adjustable sequencing systems, with different modes such as those mentioned above. In some of these modes the sequencing, or synonymously the phasing (i.e. which light(s) is/are currently green, and which are red) as well as timing of a particular phase of the lights may be varied according to demands received. As explained above, the demands may comprise at least: Manual; * Natural; * Forced; and * Nudge;

CO C

CO

Prior art systems are arranged to deal with these demands, e.g. by bringing a particular unit to green to allow passage of traffic caused by a natural demand Cif the group of units are in a VA mode for example), or by bringing a unit to green from any other demand. There is no differentiation in prior art systems between different demands. In other words, prior art systems often do not differentiate between different kinds of demand -they all have equal priority.

Also, in prior art systems when a mode is changed (such as going from fixed time to VA mode), any unserviced demands are removed. Prior art systems also start operating, when switched to a given mode (say VA or fixed timing mode), in a sequence that is not dependent upon any prior demands made upon the system.

The effect of this can be seen with an example. Assume a traffic system is installed at a 4-way junction, and so is operative as a 4-phase site, and that the timings of the phases (in seconds) are as follows in Table 1:

Table 1

Red Green Phase 1 Phase 2 Phase 3 Phase 4 If no demand in VA 20 20 20 20 35 35 35 12 12 12 12 So, each phase will be red for 20 seconds, and will be green for 35 seconds in a fixed timing mode, and also in a VA mode where there is a natural demand placed on the particular unit (e.g. because of an approaching car detected at that unit), but, if in a VA mode where no demand is detected, the phase will stay green for just 12 seconds. This is a fairly typical timing that may be encountered. Of course, there will be timings associated with the yellow light too, but they are fixed.

Assume that the site is working in a fixed time mode, and that a vehicle has approached on phase 4 -i.e. unit 4 has detected a vehicle approaching. Assume also that the mode of operation is changed to VA mode just as the system has started to serve phase 3 (i.e. the light on unit 3 has just gone green).

Table 2 below shows the timing in seconds of a typical prior art system under this situation.

The phase states that the prior art system will go through are shown in the first column, with the timing in seconds for each state being shown in the second column. Starting from phase 3 being green, with the unserviced demand on phase 4, the mode changes to VA mode, which has the effect of wiping the demand from memory, and starting the mode from its initial starting point, i.e. from phase 1. Thus, it can be seen that the vehicle waiting at unit 4 has to wait a total of 169 seconds from its arrival before it gets a green light.

Table 2

Existing systems (seconds) Phase 3 Green 35 Phase 3 Amber 3 Safety Red 20 Phase 1 Red/Amber 2 Phase 1 Green 12 Phase 1 Amber 3 Safety Red 20 Phase 2 Red/Amber 2 Phase 2 Green 12 Phase 2 Amber 3 Safety Red 20 Phase 3 Red/Amber 2 Phase 3 Green 12 Phase 3 Amber 3 Safety Red 20 Total 171 Table 3 shows the timing that occurs under the same circumstances in an embodiment of the present invention. The embodiment comprises of a traffic light system, having four units, wherein each units comprises of a red-yellow-green traffic light, and a traffic light controller. Each unit constitutes a phase, and is located at a suitable location on a junction to control the flow of traffic from that location into the junction. As the embodiment is able to remember demands that are received across a mode change, then it knows that there is a vehicle waiting on phase 4. Thus, when the mode changes to VA mode in this example, it can, once phase 3 has been completed, switch to phase 4 where the vehicle is waiting, rather than start from the beginning of the cycle as occurs with the prior art. Thus, it can be seen that the delay for the waiting vehicle is now 60 seconds, rather than the 171 seconds as with the prior art system.

Table 3

Prioritized Demand (seconds) Phase 3 Green 35 Phase 3 Amber Safety Red 3 20 Phase 4 Red/Amber 2 Total 60 The embodiment of the invention as described above comprises four units (or synonymously, four phases). Each such unit is represented in functional form in Figure 1. Traffic light unit 10 comprises of a lighting head 12, having red 14, yellow 16, and green 18 lights thereon. The unit further comprises of a radar sensor 18 mounted on the top of the unit and which is used for detecting oncoming vehicles. The unit further comprises controller 20, that itself comprises of an electronic control board, having a microprocessor, memory, including nonvolatile storage, and interfacing electronics, for controlling both the lighting head of the unit and other units with which it is in contact, and for receiving data related to sensors such as radar 18 on the unit, and other sensors on other units. A battery pack 22 also forms part of the unit 10, for providing power to drive the lighting head and control circuitry etc. The memory is used to store a demand queue, as explained herein, as well as for the use of the microprocessor in its normal operation. The controller 20 may alternatively comprise a microcontroller, FPGA, or some other type of processor or electronic device. It may comprise hardware and software, or firmware, or may be logically coded in hardware form.

Of course, other embodiments may comprise any number of units, at least one of which has a controller adapted to control the unit(s) as herein described. The units of this embodiment are in communication with each other by means of further comprising a two-way radio link. The embodiment is able to provide the improved time to service the demand because it placed the demand in a queue in memory, that was retained after the mode change, which

does not happen with prior art systems.

Another embodiment of the invention comprises of a traffic light controller that has inputs and outputs allowing for a connection to one or more traffic light units, so as to be able to control the operation of the unit(s) to which it is connected. The inputs may be, for example, the current state of a unit, sensor data from a vehicle detector, or a pedestrian crossing switch. The outputs may be the desired state of the one or more units to which it may be connected As such, this embodiment comprises essentially of the functionality of the control circuitry 20 shown in Figure 1, and which may be retrofitted to lighting units not having such a control circuit.

Figure 2 shows a flow chart 40 of the operation of the controller shown in Figure 1. It is assumed that the controller is operative in a unit, that no demands are currently unserviced, and the unit forms part of a group of lights, operational in a mode. The mode will dictate a phasing sequence, i.e. a sequence for each unit in the group, including timing for red and green, to provide traffic management through the location at which the units are installed.

The block diagram is entered at 42, where it is assumed that the units within a group already functioning. At 42 the lights in a unit are set by the controller according to their current phase CO (i.e., they are set to red or green. The particular current operating mode dictates the duration that the lights stay in the phase. At the end of that phase the controller checks at 44 to see whether any new demands have been received. If there are no new demands, then path 46 O is taken, and the next phase in the unit is activated at 48, and other units in the group are also switched to their appropriate phase according to their position in the sequence and the CD mode of operation.

If one or more new demands have been received, then path 50 is taken, then they are added to the demand list at 52, in a position according to the demand's priority. The controller then services the demand having the highest priority in the demand queue at 54, and removes the demand from the queue. After it has been serviced, it then checks at 56 to see whether the demand queue is empty. If it is, then path 58 is taken and the controller will move the lights to the next phase in the sequence, according to the current operational mode. If it isn't empty then path 60 is taken, and it will again service the demand having highest priority in the queue. The demands are processed in this fashion until the demand queue is empty, and then the sequence is resumed.

Each demand has a priority in the following order (highest priority to lowest): a) manual demand; b) natural demand; c) forced demand; and d) nudge demand.

Note that if multiple demands are received of the same type, then they are prioritized according to the time of arrival of each such demand.

The demand having the highest priority in the demand queue is serviced by appropriate phasing of the lights of all units in the group. For example, if a natural demand has come in from e.g. a radar detection of an oncoming vehicle at unit 2, then the controller will set unit 2 to green, and the other units in the group to red, to service that demand. That demand is then deleted from the queue, along with any other demands for that same phase (as they will have also now have been serviced).

Note that this flow chart does not detail the function of any particular mode, and hence it applies across all operational modes of the embodiment. Most notably, it also applies across CO changes in mode, such that if a change in mode occurs, then the demand queue is maintained.

Figure 3 shows an example of the operation of both a prior art system, and a system CD 20 according to an embodiment of the present invention, at a 4-way junction. A site comprises O of a junction has four traffic light units comprising a group, with one unit controlling the flow of traffic from each direction into the junction. The numbers in squares represent the number of the unit, and the number of the particular entry to the junction.

Firstly, operation of a prior art system will be described. Assume that the prior art units have been programmed to sequentially service the junctions according to the number of the unit. Thus, first junction 1 is serviced, then 2, 3 and 4. Also assume that the group are operational in a fixed timing mode. Whilst in the fixed time mode natural demands are created by the arrival of vehicles, in the order indicated by the numbers in circles. So, a vehicle arrived first at approach 4, then a vehicle arrived at approach 3, and finally a vehicle arrived at approach 2.

Assume that the system has just started to service phase 1 (i.e. unit 1 has just been set to green), but then the mode is changed to a VA mode. As shown by the numbers in circles, demands appeared at the approaches in the time order 4, 3, 2. However, as the prior art system does not store demands following a mode change, it will initially sequence the lights to green in the phase order 2, 3, 4, as it is programmed to do. This provides a significant wait for the traffic at junction 4, which arrived first at the junction.

In contrast an embodiment of the present invention stores the demands across a mode change, and will have prioritized them according to their time of arrival (given that they are all demands of the same type, namely natural demands), and so will switch the lights in the phase order 4, 3, 2, thus allowing the vehicles through the junction according to the order in which they arrived. This speeds up the flow of traffic, and helps to prevent driver annoyance.

Figure 4 shows a further example of the operation of a prior art system, and a system of the present invention, at a 4-way junction, but this time with a further demand from a manual controller. The unit and approach numbering remains the same, as indicated by the numbers in squares. As before, assume that the system is initially in fixed timing mode, and that natural demands have been generated by oncoming vehicles to the approaches in the order shown by the numbers in circles. So, again, vehicles, and hence natural demands, appeared CO at the approaches in the time order 4, 3, 2. Also, in this example, a manual controller to put a manual demand onto phase 3 0.e. to set unit 3 to green, e.g. to allow a buildup of traffic at that approach to be dispersed.

Then, following the generation of these demands, assume, as before, that the system has O just started to service phase 1 (i.e. unit 1 has just been set to green), but then the mode is changed to a VA mode. Because of the mode change, the prior art system would forget the various demands that have been placed, due to the natural demands and the manual controller. Thus, it would again sequence the phases in its pre-programmed order of 2, 3, 4.

In contrast, a system of the present invention, that is able to remember the demands prior to a mode change, and their relative priorities, and to act on them would sequence the phases is a different order. The order would be as presented by the numbers in triangles. I.e., the first unit to be switched to green, after unit 1 had completed its phase, would be unit 3, to service the high priority demand from the manual controller. Of course, that effectively also services the lower priority demand on unit 3 created by the detection of the vehicle at that approach. Following that, unit 4 would be serviced, as that had priority from the natural demands over unit 2, because of the earlier arrival of vehicles at that approach 4.

Thus, embodiments of the present invention are able to manage traffic flow in a much more satisfactory manner as compared to prior art systems, leading to improved traffic movement though a site controlled by a group of traffic lights.

The functions described herein as provided by individual components could, where appropriate, be provided by a combination of components instead. Similarly, functions described as provided by a combination of components could, where appropriate, be provided by a single component.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

CO Features, integers, or characteristics, described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and CO 20 drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments.

Claims (17)

1. Claims 1. A portable traffic light controller comprising a computer system arranged to have at least two inputs from respective traffic light units, and at least two outputs to the respective traffic light units, wherein the computer system comprises of a processor and memory, and wherein the control system is arranged to control lights on the at least one traffic light unit, to indicate to traffic and/or pedestrians whether to go or to stop, and further wherein it has a plurality of operating modes and facility for changing therebetween, each mode corresponding to a particular sequencing or timing arrangement for the at least two traffic light units, and further wherein the system is able to accept demands, where a demand is a request for one or more traffic light units to go to a particular state, and to service the demands by sending signals to one or more of the outputs to put the corresponding traffic light unit(s) into the particular state according to the sequencing or timing arrangement of the current mode, wherein the system is further arranged to save in memory any unserviced demands CO immediately preceding a mode change and to prioritise the unserviced demands following the mode change.
2. 2. A traffic light controller as claimed in claim 1, wherein the controller has inputs for CD 20 receiving signals from at least one vehicle sensor or other external environmental sensor for detecting the presence of waiting vehicles/pedestrians, and for receiving signals from at least one manual controller, and wherein the controller is arranged to regard signals so received as demands.
3. 3. A traffic light controller as claimed in claim 2 wherein the controller is adapted to respond to demands placed by: a) an input from the manual controller(s); b) an input from the at least one vehicle sensor, or other external environmental sensor; c) an internal timer according to sequence and timing settings of a current operating mode; and d) an internal watchdog timer
4. 4. A traffic light controller as claimed in any of claims 1 to 3, wherein the modes comprise at least: i) a fixed timing sequence mode; ii) a manual mode; and iii) a vehicle activated mode;
5. 5. A traffic light controller as claimed in claim 4, when dependent upon claim 3, wherein the controller is adapted to prioritise demands according to a prioritisation hierarchy having the order shown in claim 3, and to service any simultaneous demands according to the hierarchy.
6. 6. A traffic light controller as claimed in claim 5 wherein, following a mode change, any demands that occurred prior to the mode changes, and which remain unserviced are serviced according to the hierarchy, and wherein any demands that occur after the mode change but before any such prior demands are serviced, are themselves serviced according to the same hierarchy.
7. 7. A traffic light controller as claimed in any of the above claims that is adapted, when CO switched from a first mode to a second mode, where the second mode is one of vehicle actuated, or fixed timing mode, to start its operating sequence by prioritising a phase that has an unserviced demand associated with it.
8. 8. A traffic control system comprising a traffic light controller as claimed in any of the CD above claims, and at least two traffic light units.
9. 9. A traffic control system as claimed in claim 8 further comprising means for communicating between the traffic light units and the traffic light controller.
10. 10. A traffic control system as claimed in claim 9 wherein the means for communicating comprises of a radio link.
11. 11. A traffic control system as claimed in any of claims 8 to 10 wherein the traffic light controller is located within a portable traffic light unit.
12. 12. A traffic control system as claimed in any of claims 8 to 11 wherein each portable traffic light unit has located thereon, or connected thereto, a vehicle sensor for detecting the presence of vehicles and/or a manual push-button for indicating the presence of pedestrians.
13. 13. A traffic control system as claimed in claim 12 wherein the traffic light controller is arranged to treat a signal from a vehicle sensor or manual push-button as a demand.
14. 14. A traffic control system as claimed in claim 13 when dependent upon claim 2 or any claim dependent upon claim 2 wherein the traffic light controller is arranged to treat a signal from the manual controller as a demand.
15. 15. A traffic light control system as claimed in any of claims 8 to 14 wherein the system is arranged to record demands from vehicle sensors and/or pedestrian push buttons when in a fixed time mode, and to add such demands to a demand queue for servicing.
16. 16. A method for controlling a plurality of traffic light units, wherein the traffic light units are arranged to be operative in a plurality of different modes of operation, comprising at least a fixed timing mode, a vehicle actuated mode, and a manually controlled mode, where the mode of operation may be switched whilst the units are operative, and wherein the units are CO responsive to demands, where a demand is a request for one or more traffic light units to go to a particular state, and to service the demands by sending signals to one or more of the outputs to put the corresponding traffic light unit(s) into the particular state according to a sequencing or timing arrangement of the current mode, the method comprising the steps of a) receiving the demand; CD b) adding the demand to a demand queue in a position according to an assigned priority of the demand; c) servicing the demands according to their priority within the demand queue; d) removing serviced demands from the demand queue; 25 wherein the demand queue is maintained across mode switches.
17. 17. A computer program product comprising instructions to cause the controller of any of claims 1 to 7 to implement the method of claim 16.