WO2015159251A1 - Method and system for adaptive traffic control - Google Patents
Method and system for adaptive traffic control Download PDFInfo
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- WO2015159251A1 WO2015159251A1 PCT/IB2015/052780 IB2015052780W WO2015159251A1 WO 2015159251 A1 WO2015159251 A1 WO 2015159251A1 IB 2015052780 W IB2015052780 W IB 2015052780W WO 2015159251 A1 WO2015159251 A1 WO 2015159251A1
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- G—PHYSICS
- G08—SIGNALLING
- G08G—TRAFFIC CONTROL SYSTEMS
- G08G1/00—Traffic control systems for road vehicles
- G08G1/07—Controlling traffic signals
- G08G1/081—Plural intersections under common control
Definitions
- This invention relates to a method and system for adaptive traffic control.
- Fixed-time systems generally make use of a number of different fixed-time plans, for example, morning peak, midday, afternoon peak and evening / night time plans.
- the disadvantage of such fixed-time plans is that they are inflexible and thus not able to deal with variations in traffic flow patterns.
- Adaptive traffic control systems generally include a central controller which undertakes complex traffic modelling based on data received from strategic locations in a linked network of traffic intersections and then determines an appropriate timing for the traffic signals at each of the traffic intersections in the network.
- Examples of such adaptive traffic control systems are SCATS (Sydney Coordinated Adaptive Traffic System) and SCOOT (Split Cycle Offset Optimization Technique).
- Control variables in traffic signal control systems include phase, stage, plan, cycle time and timing offset.
- a "phase” also referred to as a "signed group” refers to a time interval for which a signal is displayed (for example, a green signal indicating right of way - the phase commences when display of the green signal commences and ends when the green signal is terminated, including any intergreen periods.
- a "stage” refers to a time interval of a signal cycle during which any combination of phases appear together.
- a "plan” refers to a time period during which a number of stages are introduced in sequence.
- a “cycle time” refers to the length of time required for each of the plan stages to appear in sequence.
- Timing offset is used to refer to a time interval separating the commencement of an operation from a traffic controller at one traffic intersection in a linked network to the next traffic controller in the network.
- Demand data is used to refer to traffic flow data representing the awaiting or moving traffic through a traffic intersection, the demand data being calculated from monitored data obtained by one or more monitoring devices monitoring traffic flow through the traffic intersection.
- any reference herein to phase, stage, plan, cycle time, timing offset and demand data shall bear the meanings attributed to them above.
- any reference herein to "link speed” shall mean a reference to the average speed of vehicles travelling from one traffic intersection to the next traffic intersection.
- volume index shall mean a reference to a measure of the volume of vehicle units at a traffic intersection.
- a method of controlling the flow of traffic through a network comprising a number of linked traffic intersections, the method including: providing a traffic controller for each traffic intersection in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersection, the traffic controller including a processor having a computer program including a traffic control algorithm, executable thereon; setting initial parameters including cycle times, stages and phases for each of the traffic controllers, together with initial timing offsets between the traffic controllers; monitoring traffic flow through each traffic intersection in order to obtain monitored data of traffic flow through the traffic intersection; the processor of each controller calculating demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; the processor of each traffic controller comparing the demand data for the traffic intersection associated therewith, with the initial parameters and adjusting the traffic intersection for the traffic cycle times, stages, phases and timing offsets of the traffic signals at the traffic intersection in order to establish revised parameters in response to differences being identified by the traffic control algorithm between the demand data
- an adaptive traffic control system for controlling the flow of traffic through a network comprising a number of linked traffic intersections, the adaptive traffic control system including: a number of monitoring devices for monitoring traffic flow through each traffic intersection in the network in order to obtain monitored data of traffic flow through the traffic intersection; a number of traffic controllers which are each associated with a different one of the traffic intersections in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersections, each traffic controller having storage means in which initial parameters are recorded, the initial parameters including cycle times, stages, phases and timing offsets between the traffic controllers, each traffic controller having a processor and a computer program including a traffic control algorithm, which when executed by the processor, is operable: a) to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; b) to compare the demand data for the traffic intersection associated therewith, with the initial parameters and to adjust at least one of cycle times, stages, phases and timing offsets of the traffic signals at the traffic
- the invention extends to one of the traffic controllers as described and defined hereinabove.
- Figure 1 shows a set of three linked traffic intersections wherein each traffic intersection has four approaches
- Figure 2 shows an overview of an adaptive traffic control system in accordance with the invention for controlling the flow of traffic through the traffic intersections shown in Figure 1 ;
- Figure 3 shows a layout of a typical single traffic intersection having four approaches, together with signals for controlling pedestrian traffic
- Figure 4 shows a graphical representation of initial control parameters for the traffic intersection of Figure 3
- Figure 5 shows a graphical representation of adjusted control parameters for the traffic intersection of Figure 3, the adjusted control parameters having been adjusted from the initial control parameters in order to complement priorities and service levels set for the vehicle approaches to the traffic intersection;
- Figure 6 shows a graphical representation of a cycle for the traffic intersection of Figure 3, in which there are no demands for pedestrians or "arrow" phases;
- Figure 7 shows graphical representation of an adjusted cycle for the traffic intersection of Figure 3, wherein the cycle of Figure 6 has been adjusted to increase the cycle time as a result of higher traffic demand for the main phase;
- Figure 8 is a graph showing vehicle flow in the traffic intersection of Figure 3 once traffic flow in the a particular direction has been given right of way;
- Figure 9 is a graph showing vehicle flow in the traffic intersection of Figure 3 in circumstances wherein there is a relatively low volume of traffic to be served yet the phase period has remained the same;
- Figures 10a and 10b show graphical representations of cycles wherein the next traffic controller (Figure 10b) is offset by 10 seconds from the dominant traffic controller ( Figure 10a);
- Figure 1 1 shows a table illustrating the manner in which the control parameters of a dominant traffic controller for the time being of a linked network of traffic intersections, is applied to the subordinate traffic controllers.
- FIG. 1 shows a set of three linked traffic intersections (junction n, junction n+1 , junction n+2).
- Figure 2 shows an overview of an adaptive traffic control system in accordance with the invention for controlling the flow of traffic through the linked traffic intersections shown in Figure 1 .
- the adaptive traffic control system in accordance with the invention is configured so as to automatically adjust the timings of the signals at each traffic intersection based on demands for service derived from strategically placed monitoring devices or sensors that gather information (“monitored data") relating to vehicles as well as pedestrians that must be served by the traffic intersections. It will be appreciated that a movement through a traffic intersection is controlled by a phase which is part of a stage.
- the traffic control system 10 comprises, broadly, a number of monitoring devices 12.1 , 12.2, 12.3 for monitoring traffic flow through each traffic intersection in order to obtain monitored data of traffic flow through the traffic intersection; a number of traffic controllers 14.1 , 14.2 and 14.3 which are each associated with the different one of the traffic intersections; and a number of recording devices 16.1 , 16.2 and 16. 3 for recording demand data calculated from the monitored data for the traffic intersections.
- Each traffic controller 14 is associated with a different one of the traffic intersections in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersections.
- Each traffic controller includes a storage module in which initial parameters are recorded, the initial parameters including cycle times, stages and phases together with initial timing offsets between the traffic controllers.
- each traffic controller has a processor and a computer program which includes a traffic control algorithm, which when executed by the processor, is operable: a) to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; b) to compare the demand data for the traffic intersection associated therewith, with the initial parameters and to adjust at least one of cycle times, stages, phases and timing offsets of the traffic signals at the traffic intersection in order to establish revised parameters in response to differences being identified by the traffic control algorithm between the demand data and the initial parameters; c) to continue to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection and to compare the demand data with any revised parameters thereby to iteratively adjust the cycle time, stages, phases and timing offsets of traffic signals at the traffic intersection in response to differences being identified by the traffic control algorithm between the demand data and the revised parameters.
- a traffic control algorithm which when executed by the processor, is operable: a) to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; b
- Each traffic controller further includes a communication module for sharing data including the demands of each traffic intersection with each of the other traffic controllers. More specifically, the computer program of each traffic controller is operable to identify from the shared data, a particular one of the traffic controllers which is associated with a traffic intersection, at which a highest demand value is monitored, as a dominant traffic controller. The computer program of each traffic controller is further operable to apply at least one of the cycle time, stage and phase of the dominant controller to the traffic controller thereby overriding any parameters of the traffic controller which are different thereto. This functionality of the traffic controllers is dealt with more fully hereinbelow.
- FIG. 3 The layout of a typical signal intersection having four approaches, together with signals for controlling pedestrian traffic, is shown in Figure 3. It will be appreciated that pedestrian traffic is allocated timing periods based on the geographic layout of the traffic intersection and timings that are mandated based on the traffic intersection layout. Ideally, timing periods to serve pedestrian traffic will be introduced when the vehicle traffic on the approaches to be crossed by pedestrians have completed the right of way through the traffic intersection, whilst turning arrow phases will be provided prior to oncoming traffic that is to be crossed by the turning traffic.
- Figure 4 shows a graphical representation of the initial control parameters for the traffic intersection of Figure 3.
- the initial default cycle time selected is 60 seconds with the main phase for vehicle traffic comprising 25 seconds with pedestrian traffic and vehicle traffic signal by a turning arrow and other phases constituting the remainder of the cycle. It will be appreciated that each movement through the traffic intersection is allocated a priority together with a level of service, with the main approaches being allocated the highest priority.
- Data sent by the monitoring device at the traffic intersection is processed by the processor to adapt the initial default settings utilising control algorithms known in the art, to a more appropriate set of timings that complement the traffic demands at the traffic intersection based on priorities in service level.
- Figure 6 depicts a cycle in which there have been no demands for pedestrian traffic or turning arrow phases.
- the signal timings now learnt for the traffic intersection are stored together with date and time related data in the storage module of the traffic controller for future recall. As time passes further recordings are made so that as traffic patterns change, traffic intersection control can be quickly re-established should there be any form of interruption to normal service.
- Signal timings continue to adapt over time to complement traffic demands as they are read and computed by the processor of each traffic controller. As demands on the traffic intersection change there will come a time when the sum of the required movement periods (stages) can no longer be complemented by the selected cycle period. When this occurs the cycle period is adjusted, either by increasing the cycle time to complement increasing demands or by lowering the cycle time during periods of low demand.
- FIG 8 is a graph showing vehicle flow in the traffic intersection of Figure 3 after traffic flow in a particular direction has been given right of way. Following a traffic signal change from "red” indicating that the traffic must remain stationery, to "green” indicating that traffic flow may commence, the slope of the curve providing information on the initial delay and the time taken for the platoon of traffic to get under way. Capacity is reached when the roadway can no longer accommodate any further traffic.
- the capacity may not be reached due to restrictions caused by congestion in the vicinity of the traffic intersection, a broken down vehicle, or a over-demand on the road network resulting in a lack of capacity downstream of the traffic intersection.
- the period of "green" time will terminate just as the traffic demand starts to diminish. Monitoring of the traffic demand by the monitoring device may result in adjustments of the cycle time and associated stages / phases.
- the method and system for controlling the flow of traffic through a network of linked traffic intersections is specifically adapted for managing traffic flow through a relatively small network of traffic intersections so as to provide a passage through a clearly defined area in order to minimise traffic delays through the area whilst still providing a balanced service to approaches intersecting the main route service.
- the demand data which is calculated from the monitored data obtained from the traffic intersections in the linked network of traffic intersections, is shared between the traffic controllers controlling traffic flow through the traffic intersections, and comprises at least the following information:
- each of the traffic controllers will commence initial operation by receiving data of local demands at the traffic intersection with which the traffic controller is associated, that is used to modify the initial default settings via the traffic control algorithms.
- the Applicant envisages that the default initial settings for cycle time and the dominant phase(s) will initially be common to all of the traffic controllers forming the link.
- a change in cycle time will be identified and this data together with other demand data is shared with the other traffic controllers forming the link.
- Each of the linked traffic controllers receives the shared demand data set which is then stored in the recording devices associated with the traffic controllers for future reference.
- the first principle of operation of the linked traffic controllers is that all of the traffic controllers that serve the same main route through the linked network of traffic intersections, operate on signal timings that best suit optimal progression of traffic through the network. Timing offsets between the traffic controllers are thus set to complement the distance and journey time through each link. Monitored data corresponding to the volumes of traffic progressing through the link as well as joining and departing the link is obtained for each link, which is used to compute the demand data pertaining to traffic intersections.
- each traffic controller is operable to identify from the shared demand data, a particular one of the traffic controllers at an traffic intersection at which a highest demand value is monitored, as a dominant (master) traffic controller and to apply at least one of the cycle time, stage and phase of the dominant traffic controller to the traffic controller, overriding any parameters of the traffic controller which are different thereto.
- a dominant traffic controller For the purposes of this discussion, the other traffic controllers in the network which are not for the time being a dominant traffic controller are referred to as "slave" controllers.
- the next traffic controller may require changes to its signal timings and offset relationship in order that the combined volume of traffic can be passed through the traffic intersections so as to not to cause a restriction in the overall progression through the set of linked traffic intersections.
- Figures 10a and Figure 10b depict cycles wherein the next traffic controller (shown in Figure 10b) is offset by 10 seconds from the dominant traffic controller (shown in Figure 10a), with each of the dominant phases being allocated 35 seconds.
- the second principle of operation of the method and system for adaptive traffic control in accordance with the invention is that the period of time allocated to the flow of traffic through the network is allocated a complementary period which takes into account the summing and dispersion of the traffic within the controlled area.
- the third principle of operation of the method and system for adaptive traffic control in accordance with the invention is that the timing offset parameters contained in demand data defined by the dominant traffic controller, are shared with the other linked traffic controllers so that the shared parameters are processed by the traffic control algorithms used by the traffic controllers at each of the traffic intersections so as to achieve steady progression of traffic flow through the linked traffic intersections in the network.
- the cycle period As the demands on the dominant controller change, so too will the cycle period. It will be appreciated that changes can be positive, increasing the cycle period, or negative decreasing the cycle period when the level of service provided by the section is exceeded. When this occurs, the cycle time as well as the timing offset of the downstream traffic controllers will need to change in order to maintain the flow progression through the link.
- the cycle times of the downstream traffic controllers will need to follow suit. This is achieved by the communication modules transmitting data via short data messages between the linked traffic controllers. Typically, data transmission will occur following the completion of each cycle period.
- the linked traffic controllers associated with the different traffic intersections will experience increasing demands that are not yet being experienced by the other traffic controllers.
- the dominant traffic controller will change according to changing traffic flow patterns, for example, during morning peak, the dominant traffic controller in the link will not be the same as the one for the afternoon peak.
- Command of the link is thus adopted by the traffic controller that is experiencing the highest demand represented by the demand data calculated for the traffic intersection, other link members that are operating with less demands are informed of the status of the dominant traffic controller via the shared data and follow the instructions issued by the command traffic controller. Should the monitored data monitored at a traffic intersection controlled by an alternative traffic controller exceed that of the current command traffic controller, command will automatically be taken over by that traffic controller.
- cycle periods can be reduced when all of the traffic controllers in the link exceed the required levels of service.
- cycle period is reduced, dominant control will move to the traffic controller still experiencing demands that cannot be satisfied by a reduce cycle period.
- the base cycle of all of the linked traffic controllers until a minimum cycle period is reached, offering the least delay to any awaiting service.
- a new series of link adjustments will automatically commence in the manner described hereinabove.
- each traffic controller maintain a register of the demand data comprising the information used to manage traffic flow at the traffic intersections which service personnel may review in order to gain an appreciation of the functional state of the traffic control at the traffic intersection.
- Figure 1 1 shows a table illustrating the manner in which the control parameters of a dominant traffic controller for the time being is applied to the subordinate (slave) traffic controllers.
- the first row of the table indicates the controller identification number for each of the different traffic controllers forming the link.
- the cycle time value is 80 second.
- the third row of the table reflects the cycle time associated with each of the linked traffic controllers, the first value "80" reflecting that the master traffic controller requirements that had been adopted, while the second value reflects the cycle time that would otherwise be appropriate for the relevant traffic intersection controlled by the traffic controller based on the traffic controller's assessment of the local traffic conditions at the traffic intersection.
- the fourth row of the table details the interval that has been given to the dominant phase / stage.
- the fifth row of the table specifies the distances entered when setting up the link of traffic controllers.
- the offset values that had been calculated based on traffic volumes being served by the linked traffic controllers the offset values being the offset times between the traffic controller 231 and its immediate neighbours and those traffic controllers remote therefrom in the network. It will be appreciated that negative values indicate that the traffic controller is upstream of the current location of the dominant controller while positive values reflect that the traffic controller is downstream of the current location. The positive and negative signs thus provide an indication of the demand flow. As dominant control is switched between the link traffic controllers, link offset values and their signs will change to complement the traffic progression at that time.
- the data is periodically saved so that in the event of a fault or an electrical mains supply failure, service can be resumed which most closely matches that time of the day. Should any of the traffic controllers in the link drop out of service, the link will be broken and traffic control measures will become unstable, to cater for this eventuality.
- the Applicant envisages that traffic controllers that are still able to communicate with their immediate neighbours will continue operation as a sub-link. Thus, for example, if controller 231 in Figure 1 1 were to become defective, two sub-links would be formed, namely a sub-link, consisting of traffic controllers 1 10 and 122 and a sub-link consisting of traffic controllers 144, 156 and 316. As link operation and traffic flows will be compromised due to a defective traffic controller, data recordal by the recording devices will be suspended.
- demand data is shared by each traffic controller to its immediate neighbours. These neighbours in turn share their own demand data and shared demand data communicated to them, with their neighbours so that in this manner a complete demand data transmission link is formed between all of the traffic controllers in which demand data pertaining to each traffic controller is shared with all the other traffic controllers.
- the method and system is for adaptive traffic controller in accordance with the invention, thus enables a number of linked traffic controllers to learn and implement signal timings that best serve users of the traffic intersections in the network. This is achieved without the need for pre-programmed timing sets which are provided to traffic controllers in advance or communicated to the individual traffic controllers from a central command centre either in the form of direct commands that switch the local phases / stages in and out of operation, or updated plan data that is then stored and referenced by the local traffic controllers.
- traffic controllers when identified to each other and provided with the basic set of information relating to their locations, learn and interact with each other so that an effective passage through the set of traffic intersections can be achieved in a fully automated manner without the need for centralized control.
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Abstract
An adaptive control system 10 for controlling flow of traffic through a network of linked traffic intersections, is configured to automatically adjust the timings of the signals at each intersection based on demands for service derived from strategically placed monitoring devices 12. The control system includes the monitoring devices 12, traffic controllers 14 for each intersection and recording devices 16 for recording demand traffic flow data for the intersections calculated from the monitored data. Each traffic controller has a processor and a traffic control algorithm which when executed by the processor, calculates demand data from monitored data, compares the demand data with initial parameters and establishes revised parameters based on differences between the demand data and the initial parameters, continues to calculate demand data for the traffic intersections from monitored data obtained from the intersections and compares the demand data with revised parameters so as to iteratively adjust the timings of the traffic signals.
Description
METHOD AND SYSTEM FOR ADAPTIVE TRAFFIC CONTROL
FIELD OF INVENTION This invention relates to a method and system for adaptive traffic control.
BACKGROUND TO INVENTION
Known urban traffic control systems generally fall into three main categories, namely, fixed-time, vehicle actuated and adaptive traffic control systems. Fixed-time systems generally make use of a number of different fixed-time plans, for example, morning peak, midday, afternoon peak and evening / night time plans. The disadvantage of such fixed-time plans is that they are inflexible and thus not able to deal with variations in traffic flow patterns.
Adaptive traffic control systems generally include a central controller which undertakes complex traffic modelling based on data received from strategic locations in a linked network of traffic intersections and then determines an appropriate timing for the traffic signals at each of the traffic intersections in the network. Examples of such adaptive traffic control systems are SCATS (Sydney Coordinated Adaptive Traffic System) and SCOOT (Split Cycle Offset Optimization Technique).
Control variables in traffic signal control systems include phase, stage, plan, cycle time and timing offset. A "phase" (also referred to as a "signed group") refers to a time interval for which a signal is displayed (for example, a green signal indicating right of way - the phase commences when display of the green signal commences and ends when the green signal is terminated, including any intergreen periods. A "stage" refers to a time interval of a signal cycle during which any combination of phases appear together.
A "plan" refers to a time period during which a number of stages are introduced in sequence.
A "cycle time" refers to the length of time required for each of the plan stages to appear in sequence.
"Timing offset" is used to refer to a time interval separating the commencement of an operation from a traffic controller at one traffic intersection in a linked network to the next traffic controller in the network.
"Demand data" is used to refer to traffic flow data representing the awaiting or moving traffic through a traffic intersection, the demand data being calculated from monitored data obtained by one or more monitoring devices monitoring traffic flow through the traffic intersection.
Any reference herein to phase, stage, plan, cycle time, timing offset and demand data shall bear the meanings attributed to them above.
In addition, any reference herein to "link speed" shall mean a reference to the average speed of vehicles travelling from one traffic intersection to the next traffic intersection.
Furthermore, any reference herein to "volume index" shall mean a reference to a measure of the volume of vehicle units at a traffic intersection.
SUMMARY OF INVENTION According to a first aspect of the invention there is provided a method of controlling the flow of traffic through a network comprising a number of linked traffic intersections, the method including: providing a traffic controller for each traffic intersection in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersection, the traffic controller including a processor having a computer program including a traffic control algorithm, executable thereon; setting initial parameters including cycle times, stages and phases for each of the traffic controllers, together with initial timing offsets between the traffic controllers; monitoring traffic flow through each traffic intersection in order to obtain monitored data of traffic flow through the traffic intersection; the processor of each controller calculating demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; the processor of each traffic controller comparing the demand data for the traffic intersection associated therewith, with the initial parameters and adjusting the traffic intersection for the traffic cycle times, stages, phases and timing offsets of the traffic signals at the traffic intersection in order to establish revised parameters in response to
differences being identified by the traffic control algorithm between the demand data and the initial parameters; continuing to monitor traffic flow through each traffic intersection and the processor of each traffic controller calculating demand data from the monitored data obtained for each traffic intersection and comparing the demand data for each traffic intersection with the initial parameters or any revised parameters and thereby iteratively adjusting the cycle times, stages, phases and timing offsets of traffic signals at the traffic intersections in response to differences being identified by the traffic control algorithm between the demand data and the initial parameters or any revised parameters; recording the demand data for each traffic intersection; sharing the demand data for each traffic intersection with the traffic controllers associated with the other traffic intersections in the network; and identifying from time to time a particular one of the traffic controllers at a traffic intersection at which the highest demands are identified, represented by the demand data calculated for the traffic intersection, as a dominant traffic controller and applying at least one of the cycle time, stages, phases and timing offsets of the dominant traffic controller to the other traffic controllers in the network, overriding any parameters of the other traffic controllers which are different thereto.
According to a second aspect of the invention there is provided an adaptive traffic control system for controlling the flow of traffic through a network comprising a number of linked traffic intersections, the adaptive traffic control system including: a number of monitoring devices for monitoring traffic flow through each traffic intersection in the network in order to obtain monitored data of traffic flow through the traffic intersection;
a number of traffic controllers which are each associated with a different one of the traffic intersections in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersections, each traffic controller having storage means in which initial parameters are recorded, the initial parameters including cycle times, stages, phases and timing offsets between the traffic controllers, each traffic controller having a processor and a computer program including a traffic control algorithm, which when executed by the processor, is operable: a) to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; b) to compare the demand data for the traffic intersection associated therewith, with the initial parameters and to adjust at least one of cycle times, stages, phases and timing offsets of the traffic signals at the traffic intersection in order to establish revised parameters in response to differences being identified by the traffic control algorithm between the demand data and the initial parameters; and c) to continue to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection and to compare the demand data with any revised parameters thereby to iteratively adjust the cycle time, stages, phases and timing offsets of traffic signals at the traffic intersection in response to differences being identified by the traffic control algorithm between the demand data and the revised parameters; recording means for recording the demand data for each traffic intersection; communication means for sharing demand data for each traffic intersection with the traffic controllers associated with the other traffic intersections in the network, the computer program of each traffic controller being operable to identify from the shared demand data, a particular one of the traffic controllers which is associated with a
traffic intersection at which a highest demand value is identified, represented by the demand data calculated for the traffic intersection, as a dominant traffic controller and to apply at least one of the cycle time, stage, phase and timing offset of the dominant traffic controller to the traffic controller, overriding any parameters of the traffic controller which are different thereto.
The invention extends to one of the traffic controllers as described and defined hereinabove.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features of the invention are described hereinafter with reference to a non- limiting example of the invention and as illustrated in the accompanying diagrammatic drawings. In the drawings:
Figure 1 shows a set of three linked traffic intersections wherein each traffic intersection has four approaches; Figure 2 shows an overview of an adaptive traffic control system in accordance with the invention for controlling the flow of traffic through the traffic intersections shown in Figure 1 ;
Figure 3 shows a layout of a typical single traffic intersection having four approaches, together with signals for controlling pedestrian traffic;
Figure 4 shows a graphical representation of initial control parameters for the traffic intersection of Figure 3; Figure 5 shows a graphical representation of adjusted control parameters for the traffic intersection of Figure 3, the adjusted control parameters having been adjusted from the
initial control parameters in order to complement priorities and service levels set for the vehicle approaches to the traffic intersection;
Figure 6 shows a graphical representation of a cycle for the traffic intersection of Figure 3, in which there are no demands for pedestrians or "arrow" phases;
Figure 7 shows graphical representation of an adjusted cycle for the traffic intersection of Figure 3, wherein the cycle of Figure 6 has been adjusted to increase the cycle time as a result of higher traffic demand for the main phase;
Figure 8 is a graph showing vehicle flow in the traffic intersection of Figure 3 once traffic flow in the a particular direction has been given right of way;
Figure 9 is a graph showing vehicle flow in the traffic intersection of Figure 3 in circumstances wherein there is a relatively low volume of traffic to be served yet the phase period has remained the same;
Figures 10a and 10b show graphical representations of cycles wherein the next traffic controller (Figure 10b) is offset by 10 seconds from the dominant traffic controller (Figure 10a); and
Figure 1 1 shows a table illustrating the manner in which the control parameters of a dominant traffic controller for the time being of a linked network of traffic intersections, is applied to the subordinate traffic controllers.
DESCRIPTION OF PREFERRED EMBODIMENTS
A method and a system for controlling the flow of traffic through a network comprising a number of linked traffic intersections, in accordance with the invention, are described hereinafter with reference to Figures 1 to 1 1 .
Figure 1 shows a set of three linked traffic intersections (junction n, junction n+1 , junction n+2). Figure 2 shows an overview of an adaptive traffic control system in accordance with the invention for controlling the flow of traffic through the linked traffic intersections shown in Figure 1 . The adaptive traffic control system in accordance with the invention, is configured so as to automatically adjust the timings of the signals at each traffic intersection based on demands for service derived from strategically placed monitoring devices or sensors that gather information ("monitored data") relating to vehicles as well as pedestrians that must be served by the traffic intersections. It will be appreciated that a movement through a traffic intersection is controlled by a phase which is part of a stage.
With reference to Figure 2 of the drawings, the adaptive traffic control system in accordance with the invention is designated generally by the reference numeral 10. The traffic control system 10 comprises, broadly, a number of monitoring devices 12.1 , 12.2, 12.3 for monitoring traffic flow through each traffic intersection in order to obtain monitored data of traffic flow through the traffic intersection; a number of traffic controllers 14.1 , 14.2 and 14.3 which are each associated with the different one of the traffic intersections; and a number of recording devices 16.1 , 16.2 and 16. 3 for recording demand data calculated from the monitored data for the traffic intersections.
Each traffic controller 14 is associated with a different one of the traffic intersections in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersections. Each traffic controller includes a storage module in which initial parameters are recorded, the initial parameters including cycle times, stages and phases together with initial timing offsets between the traffic controllers. As such, each traffic controller has a processor and a computer program which includes a traffic control algorithm, which when executed by the processor, is operable:
a) to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; b) to compare the demand data for the traffic intersection associated therewith, with the initial parameters and to adjust at least one of cycle times, stages, phases and timing offsets of the traffic signals at the traffic intersection in order to establish revised parameters in response to differences being identified by the traffic control algorithm between the demand data and the initial parameters; c) to continue to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection and to compare the demand data with any revised parameters thereby to iteratively adjust the cycle time, stages, phases and timing offsets of traffic signals at the traffic intersection in response to differences being identified by the traffic control algorithm between the demand data and the revised parameters.
Each traffic controller further includes a communication module for sharing data including the demands of each traffic intersection with each of the other traffic controllers. More specifically, the computer program of each traffic controller is operable to identify from the shared data, a particular one of the traffic controllers which is associated with a traffic intersection, at which a highest demand value is monitored, as a dominant traffic controller. The computer program of each traffic controller is further operable to apply at least one of the cycle time, stage and phase of the dominant controller to the traffic controller thereby overriding any parameters of the traffic controller which are different thereto. This functionality of the traffic controllers is dealt with more fully hereinbelow.
The layout of a typical signal intersection having four approaches, together with signals for controlling pedestrian traffic, is shown in Figure 3. It will be appreciated that pedestrian traffic is allocated timing periods based on the geographic layout of the traffic intersection and timings that are mandated based on the traffic intersection layout.
Ideally, timing periods to serve pedestrian traffic will be introduced when the vehicle traffic on the approaches to be crossed by pedestrians have completed the right of way through the traffic intersection, whilst turning arrow phases will be provided prior to oncoming traffic that is to be crossed by the turning traffic.
Figure 4 shows a graphical representation of the initial control parameters for the traffic intersection of Figure 3. The initial default cycle time selected is 60 seconds with the main phase for vehicle traffic comprising 25 seconds with pedestrian traffic and vehicle traffic signal by a turning arrow and other phases constituting the remainder of the cycle. It will be appreciated that each movement through the traffic intersection is allocated a priority together with a level of service, with the main approaches being allocated the highest priority. Data sent by the monitoring device at the traffic intersection is processed by the processor to adapt the initial default settings utilising control algorithms known in the art, to a more appropriate set of timings that complement the traffic demands at the traffic intersection based on priorities in service level.
With reference to Figure 5, it can be seen how the initial default timing period has been adjusted based on data received from the monitoring device associated with the traffic intersection, to complement the priorities and service levels set for the approaches. While it is likely that the cycle time may also adjusted so as to complement the priorities in service levels set for the approaches, in Figure 5, the cycle time has been maintained at 60 seconds in order to simplify the explanation of the operation of the system. In Figure 5 it can be seen clearly that the main phase has been allocated a greater proportion of the cycle compared to the other approaches. Pedestrian service will not necessarily be demanded during each cycle, in which case the periods that have been allocated to pedestrian traffic may be added to vehicle traffic service.
Figure 6 depicts a cycle in which there have been no demands for pedestrian traffic or turning arrow phases. Following an initial learning period, the signal timings now learnt for the traffic intersection are stored together with date and time related data in the
storage module of the traffic controller for future recall. As time passes further recordings are made so that as traffic patterns change, traffic intersection control can be quickly re-established should there be any form of interruption to normal service. Signal timings continue to adapt over time to complement traffic demands as they are read and computed by the processor of each traffic controller. As demands on the traffic intersection change there will come a time when the sum of the required movement periods (stages) can no longer be complemented by the selected cycle period. When this occurs the cycle period is adjusted, either by increasing the cycle time to complement increasing demands or by lowering the cycle time during periods of low demand. Known traffic control algorithms are used for computing the adjustments. It will be appreciated that adjustments of the cycle time are introduced in minor increments at the beginning of each cycle, the cycle time and period of the significant main approach being stored in the storage module of the traffic controller associated with the traffic intersection. This data is used to form part of the shared data which is used to manage a linked network of traffic intersections of which the traffic intersection forms part as is dealt with in more detail hereinbelow.
With reference to Figure 7, it can be seen that the cycle time has been increased to 70 seconds in response to higher traffic demands for the main phase, 45 seconds of which is allocated to the main phase. In the above examples, signal timings for the phases have been calculated based on control algorithms providing the required level of service based on the priorities allocated to each of the services to be provided at the traffic intersection. Figure 8 is a graph showing vehicle flow in the traffic intersection of Figure 3 after traffic flow in a particular direction has been given right of way. Following a traffic signal change from "red" indicating that the traffic must remain stationery, to "green" indicating that traffic flow may commence, the slope of the curve providing information on the initial delay and the time taken for the platoon of traffic to get under way. Capacity is reached when the roadway can no longer accommodate any further traffic. This may be as a result of a speed restriction or a limitation of the road geometry. At times the
capacity may not be reached due to restrictions caused by congestion in the vicinity of the traffic intersection, a broken down vehicle, or a over-demand on the road network resulting in a lack of capacity downstream of the traffic intersection. Ideally, the period of "green" time will terminate just as the traffic demand starts to diminish. Monitoring of the traffic demand by the monitoring device may result in adjustments of the cycle time and associated stages / phases.
The timing and demand relationship is further illustrated in Figure 9 which graphically represents a situation in which there is a low volume of traffic to be served yet the phase period has remained the same. Once the peak of the traffic flow has been reached, much of the remaining phase period is not being used optimally and this excess time could be provided to serve other awaiting users at the traffic intersection. The Applicant envisages that each of the vehicle movement through the traffic intersection is measured in a similar manner, with the data of the vehicle movements monitored by the monitoring devices at the traffic intersection being combined to influence the overall cycle time requirement.
The above description provides background information on the operation of a standalone traffic controller at a traffic intersection. It will be appreciated, that however, that the method and system for adaptive traffic control in accordance with the invention is configured for controlling the flow of traffic through a network comprising a number of linked traffic intersections such as the traffic intersection shown in Figure 1 .
The method and system for controlling the flow of traffic through a network of linked traffic intersections is specifically adapted for managing traffic flow through a relatively small network of traffic intersections so as to provide a passage through a clearly defined area in order to minimise traffic delays through the area whilst still providing a balanced service to approaches intersecting the main route service. The demand data which is calculated from the monitored data obtained from the traffic intersections in the linked network of traffic intersections, is shared between the traffic
controllers controlling traffic flow through the traffic intersections, and comprises at least the following information:
Traffic controller ID
Controller status (master or slave)
Cycle time
Critical phase / stage period
Traffic density / time
Offset parameters
Traffic volume index
Traffic link speed
As is stated hereinabove, each of the traffic controllers will commence initial operation by receiving data of local demands at the traffic intersection with which the traffic controller is associated, that is used to modify the initial default settings via the traffic control algorithms. The Applicant envisages that the default initial settings for cycle time and the dominant phase(s) will initially be common to all of the traffic controllers forming the link. In operation, as soon as the first traffic controller computes that the cycle time of the controller does not complement the level of service settings, a change in cycle time will be identified and this data together with other demand data is shared with the other traffic controllers forming the link. Each of the linked traffic controllers receives the shared demand data set which is then stored in the recording devices associated with the traffic controllers for future reference. The first principle of operation of the linked traffic controllers is that all of the traffic controllers that serve the same main route through the linked network of traffic intersections, operate on signal timings that best suit optimal progression of traffic through the network. Timing offsets between the traffic controllers are thus set to complement the distance and journey time through each link. Monitored data corresponding to the volumes of traffic progressing through the link as well as joining and departing the link is obtained for each link, which is used to compute the demand
data pertaining to traffic intersections. The computer program of each traffic controller is operable to identify from the shared demand data, a particular one of the traffic controllers at an traffic intersection at which a highest demand value is monitored, as a dominant (master) traffic controller and to apply at least one of the cycle time, stage and phase of the dominant traffic controller to the traffic controller, overriding any parameters of the traffic controller which are different thereto. For the purposes of this discussion, the other traffic controllers in the network which are not for the time being a dominant traffic controller are referred to as "slave" controllers. For example, if at a particular traffic intersection, the main phase and traffic from an opposing phase combined to become a dominant flow for the main phase at the next traffic controller in the link, then the next traffic controller may require changes to its signal timings and offset relationship in order that the combined volume of traffic can be passed through the traffic intersections so as to not to cause a restriction in the overall progression through the set of linked traffic intersections.
Figures 10a and Figure 10b depict cycles wherein the next traffic controller (shown in Figure 10b) is offset by 10 seconds from the dominant traffic controller (shown in Figure 10a), with each of the dominant phases being allocated 35 seconds. The second principle of operation of the method and system for adaptive traffic control in accordance with the invention, is that the period of time allocated to the flow of traffic through the network is allocated a complementary period which takes into account the summing and dispersion of the traffic within the controlled area. The third principle of operation of the method and system for adaptive traffic control in accordance with the invention, is that the timing offset parameters contained in demand data defined by the dominant traffic controller, are shared with the other linked traffic controllers so that the shared parameters are processed by the traffic control algorithms used by the traffic controllers at each of the traffic intersections so as to achieve steady progression of traffic flow through the linked traffic intersections in the network. As the demands on the dominant controller change, so too will the cycle period. It will be
appreciated that changes can be positive, increasing the cycle period, or negative decreasing the cycle period when the level of service provided by the section is exceeded. When this occurs, the cycle time as well as the timing offset of the downstream traffic controllers will need to change in order to maintain the flow progression through the link. Thus, as the cycle time of the dominant traffic controller increases or decreases, the cycle times of the downstream traffic controllers will need to follow suit. This is achieved by the communication modules transmitting data via short data messages between the linked traffic controllers. Typically, data transmission will occur following the completion of each cycle period.
At different times of the day or on different days of the week, the linked traffic controllers associated with the different traffic intersections, will experience increasing demands that are not yet being experienced by the other traffic controllers. As such, the dominant traffic controller will change according to changing traffic flow patterns, for example, during morning peak, the dominant traffic controller in the link will not be the same as the one for the afternoon peak. Command of the link is thus adopted by the traffic controller that is experiencing the highest demand represented by the demand data calculated for the traffic intersection, other link members that are operating with less demands are informed of the status of the dominant traffic controller via the shared data and follow the instructions issued by the command traffic controller. Should the monitored data monitored at a traffic intersection controlled by an alternative traffic controller exceed that of the current command traffic controller, command will automatically be taken over by that traffic controller. As the demands on the linked traffic controllers begin to reduce, cycle periods can be reduced when all of the traffic controllers in the link exceed the required levels of service. As the cycle period is reduced, dominant control will move to the traffic controller still experiencing demands that cannot be satisfied by a reduce cycle period. As the traffic demands in the network of traffic intersections reduced, so too will the base cycle of all of the linked traffic controllers until a minimum cycle period is reached, offering the least delay to any awaiting service. As soon as new demands start to be
recorded that exceed the minimum operating cycle, a new series of link adjustments will automatically commence in the manner described hereinabove.
It will be appreciated that the recording devices associated with each traffic controller maintain a register of the demand data comprising the information used to manage traffic flow at the traffic intersections which service personnel may review in order to gain an appreciation of the functional state of the traffic control at the traffic intersection.
Figure 1 1 shows a table illustrating the manner in which the control parameters of a dominant traffic controller for the time being is applied to the subordinate (slave) traffic controllers. The first row of the table indicates the controller identification number for each of the different traffic controllers forming the link. In the second row of the table, only the cycle time of the current master traffic controller (controller 231 ) is reflected, the cycle time value being 80 second. The third row of the table reflects the cycle time associated with each of the linked traffic controllers, the first value "80" reflecting that the master traffic controller requirements that had been adopted, while the second value reflects the cycle time that would otherwise be appropriate for the relevant traffic intersection controlled by the traffic controller based on the traffic controller's assessment of the local traffic conditions at the traffic intersection.
The fourth row of the table details the interval that has been given to the dominant phase / stage. The fifth row of the table specifies the distances entered when setting up the link of traffic controllers. In the sixth row of the table, the offset values that had been calculated based on traffic volumes being served by the linked traffic controllers, the offset values being the offset times between the traffic controller 231 and its immediate neighbours and those traffic controllers remote therefrom in the network. It will be appreciated that negative values indicate that the traffic controller is upstream of the current location of the dominant controller while positive values reflect that the traffic controller is downstream of the current location. The positive and negative signs thus provide an indication of the demand flow.
As dominant control is switched between the link traffic controllers, link offset values and their signs will change to complement the traffic progression at that time. The data is periodically saved so that in the event of a fault or an electrical mains supply failure, service can be resumed which most closely matches that time of the day. Should any of the traffic controllers in the link drop out of service, the link will be broken and traffic control measures will become unstable, to cater for this eventuality. The Applicant envisages that traffic controllers that are still able to communicate with their immediate neighbours will continue operation as a sub-link. Thus, for example, if controller 231 in Figure 1 1 were to become defective, two sub-links would be formed, namely a sub-link, consisting of traffic controllers 1 10 and 122 and a sub-link consisting of traffic controllers 144, 156 and 316. As link operation and traffic flows will be compromised due to a defective traffic controller, data recordal by the recording devices will be suspended.
It will be appreciated that during normal operation demand data is shared by each traffic controller to its immediate neighbours. These neighbours in turn share their own demand data and shared demand data communicated to them, with their neighbours so that in this manner a complete demand data transmission link is formed between all of the traffic controllers in which demand data pertaining to each traffic controller is shared with all the other traffic controllers.
The method and system is for adaptive traffic controller in accordance with the invention, thus enables a number of linked traffic controllers to learn and implement signal timings that best serve users of the traffic intersections in the network. This is achieved without the need for pre-programmed timing sets which are provided to traffic controllers in advance or communicated to the individual traffic controllers from a central command centre either in the form of direct commands that switch the local phases / stages in and out of operation, or updated plan data that is then stored and referenced by the local traffic controllers. Hence, traffic controllers, when identified to each other and provided with the basic set of information relating to their locations, learn and interact with each other so that an effective passage through the set of traffic
intersections can be achieved in a fully automated manner without the need for centralized control.
Claims
1 . A method of controlling the flow of traffic through a network comprising a number of linked traffic intersections, the method including: providing a traffic controller for each traffic intersection in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersection, the traffic controller including a processor having a computer program including a traffic control algorithm, executable thereon; setting initial parameters including cycle times, stages and phases for each of the traffic controllers, together with initial timing offsets between the traffic controllers; monitoring traffic flow through each traffic intersection in order to obtain monitored data of traffic flow through the traffic intersection; the processor of each controller calculating demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; the processor of each traffic controller comparing the demand data for the traffic intersection associated therewith, with the initial parameters and adjusting the traffic intersection for the traffic cycle times, stages, phases and timing offsets of the traffic signals at the traffic intersection in order to establish revised parameters in response to differences being identified by the traffic control algorithm between the demand data and the initial parameters; continuing to monitor traffic flow through each traffic intersection and the processor of each traffic controller calculating demand data from the monitored data obtained for each traffic intersection and comparing the demand data for each traffic
intersection with the initial parameters or any revised parameters and thereby iteratively adjusting the cycle times, stages, phases and timing offsets of traffic signals at the traffic intersections in response to differences being identified by the traffic control algorithm between the demand data and the initial parameters or any revised parameters; recording the demand data for each traffic intersection; sharing the demand data for each traffic intersection with the traffic controllers associated with the other traffic intersections in the network; and identifying from time to time a particular one of the traffic controllers at a traffic intersection at which the highest demands are identified, represented by the demand data calculated for the traffic intersection, as a dominant traffic controller and applying at least one of the cycle time, stages, phases and timing offsets of the dominant traffic controller to the other traffic controllers in the network, overriding any parameters of the other traffic controllers which are different thereto.
2. An adaptive traffic control system for controlling the flow of traffic through a network comprising a number of linked traffic intersections, the adaptive traffic control system including: a number of monitoring devices for monitoring traffic flow through each traffic intersection in the network in order to obtain monitored data of traffic flow through the traffic intersection; a number of traffic controllers which are each associated with a different one of the traffic intersections in the network for controlling parameters including cycle times, stages, phases and timing offsets of traffic signals at the traffic intersections, each traffic controller having storage means in which initial parameters are recorded,
the initial parameters including cycle times, stages, phases and timing offsets between the traffic controllers, each traffic controller having a processor and a computer program including a traffic control algorithm, which when executed by the processor, is operable: a) to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection; b) to compare the demand data for the traffic intersection associated therewith, with the initial parameters and to adjust at least one of cycle times, stages, phases and timing offsets of the traffic signals at the traffic intersection in order to establish revised parameters in response to differences being identified by the traffic control algorithm between the demand data and the initial parameters; and c) to continue to calculate demand data for the traffic intersection associated therewith, from the monitored data obtained from the traffic intersection and to compare the demand data with any revised parameters thereby to iteratively adjust the cycle time, stages, phases and timing offsets of traffic signals at the traffic intersection in response to differences being identified by the traffic control algorithm between the demand data and the revised parameters; recording means for recording the demand data for each traffic intersection; communication means for sharing demand data for each traffic intersection with the traffic controllers associated with the other traffic intersections in the network, the computer program of each traffic controller being operable to identify from the shared demand data, a particular one of the traffic controllers which is associated with a traffic intersection at which a highest demand value is identified, represented
by the demand data calculated for the traffic intersection, as a dominant traffic controller and to apply at least one of the cycle time, stage, phase and timing offset of the dominant traffic controller to the traffic controller, overriding any parameters of the traffic controller which are different thereto.
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| ZA2014/02833 | 2014-04-16 | ||
| ZA201402833 | 2014-04-16 |
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| WO2015159251A1 true WO2015159251A1 (en) | 2015-10-22 |
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| PCT/IB2015/052780 WO2015159251A1 (en) | 2014-04-16 | 2015-04-16 | Method and system for adaptive traffic control |
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| CN106683450A (en) * | 2017-01-25 | 2017-05-17 | 东南大学 | Recognition method for key paths of urban signal control intersection groups |
| CN107945539A (en) * | 2017-08-28 | 2018-04-20 | 北京工业大学 | A kind of intersection signal control method |
| WO2018227157A1 (en) * | 2017-06-09 | 2018-12-13 | University Of Southern California | Adaptive traffic control |
| CN109345031A (en) * | 2018-10-26 | 2019-02-15 | 江苏智通交通科技有限公司 | Coordination trunk line planing method and configuration system based on traffic flow data |
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| CN105913673A (en) * | 2016-05-18 | 2016-08-31 | 杭州智诚惠通科技有限公司 | Large-scale road network signal lamp estimation method |
| CN106683450A (en) * | 2017-01-25 | 2017-05-17 | 东南大学 | Recognition method for key paths of urban signal control intersection groups |
| CN106683450B (en) * | 2017-01-25 | 2019-06-04 | 东南大学 | A kind of urban signal controlling intersection group critical path recognition methods |
| WO2018227157A1 (en) * | 2017-06-09 | 2018-12-13 | University Of Southern California | Adaptive traffic control |
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| CN109345031B (en) * | 2018-10-26 | 2021-07-20 | 江苏智通交通科技有限公司 | Coordinated trunk line planning method and configuration system based on traffic flow data |
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