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Dublin Traffic Cameras
Adaptive road traffic control systems in use in Ireland
The SCATS (Sydney Coordinated Adaptive Traffic System) is used in Dublin City. The system controls some 180 intersections (out of 1,000 odd controllers) in the Dublin Corporation area (incredibly traffic signals in South Dublin and Fingal have no management or coordination system, while Dun Laoghaire/Rathdown plan to introduce SCATS control on a few intersections before 2005).
SCATS gathers data on traffic flows
in real-time at each intersection. This data is fed via the traffic control signal box to
a central computer. The computer makes incremental adjustments to traffic light timings based on minute by minute
changes in traffic flow at each intersection. SCATS performs a vehicle count at each stop line, and also
measures the gap between vehicles as they pass through each junction. As the gap between vehicles increases
the lights are wasting green time, and SCATS seeks to reallocate green time to where demand is greatest.
The SCATS system is also used in many other urban areas including Hong Kong, Sydney (where it originated), Melbourne, and Oakland County (MI).
Cork City is installing the SCOOT (Split Cycle Offset Optimization Technique) system during 1997/99. SCOOT differs from SCATS
in that it uses a second set of advance vehicle detectors typically 50-300 metres upstream of the stop line.
The advance detectors provide a count of the vehicles approaching at each junction. This gives
the system a higher resolution picture of traffic flows and a count of the number of vehicles in each queue, several seconds before they
touch the stop line (allowing time for communication between the traffic signal controller and
the central SCOOT computer). It also provides exceptional queue length detection information to the
system, which is triggered when the traffic queue backs up to the upstream detector. Under the SCOOT system green waves can be dynamically delayed on a "just in time" basis based on the arrival of vehicles at the upstream detector, allowing extra time to the previous green phase where warranted in heavy traffic conditions.
The SCOOT model has three optimizers:
At every junction and for every phase, the split optimizer, a few seconds before the phase change is due to take place, will make a decision as to whether to make the change earlier, later or as due. The optimizer implements the decision, which only affects the phase change time by a few seconds, that minimizes the maximum degree of saturation for the approaches to the intersection.
During a predetermined phase in each cycle, and for every junction in the system, the offset optimizer makes a decision to alter, by a fixed amount, all the scheduled change times. The optimizer uses information stored in the cyclic flow profiles and by comparing the sum of the PIís on all the adjacent LINKs for the scheduled offset and the possible changed offsets.
Cycle Time Optimizer
A SCOOT system is split into cycle time REGIONs which have pre-determined minimum and maximum timing boundaries. The optimizer can vary the cycle time of each REGION in small intervals to attempt to ensure that the most heavily loaded NODE in the system is operating at a 90% saturation. If all stop bars are operating at less than 90% then the optimizer will make incremental reductions in cycle time.
How does SCOOT work in practice?
If one takes the example of a busy arterial road with side roads intersecting it, a SCOOT controlled traffic signal system will seek to maximize the traffic carrying capacity of the arterial road by slotting traffic flows from the side road, far side turn filters, and pedestrian crossing phases into predicted gaps in vehicle flows along the arterial route. The SCOOT system uses upstream vehicle detectors to predict vehicle arrivals at the stop line, in advance of real time. Upstream detectors on the side roads give the system information on queue lengths, which in turn allows it to maximise the green wave along the arterial route, by recovering un-needed green time allocated to non-priority phases. As the AM and PM traffic peaks, SCOOT increases the cycle time dramatically to assist traffic flow fluidity along main routes by reducing the incidence of start/stop events which might otherwise bring traffic to a standstill.
The SCOOT system is used in many other urban areas, including Toronto, San Diego, Anaheim, London, and Bangkok..
Presentation on SCOOT (Adobe Postscript format)
Presentation on SCATS (Adobe Postscript format)
Synchro Plus (2.7MB) Windows PC compatible traffic simulation software demo from Trafficware . While the demo does not support SI (metric) measurements, it is otherwise well designed and provides a useful insight into traffic planning variables, showing how optimization of cycle and phase times for a given traffic volume can reduce traffic queues and delays, using a dozen or so different junction designs.System requirements and license agreement.
UTOPIA / SPOT
In use in Scandinavia (Goteborg and Oslo) and Italy (Turin / Salerno), and experimentally in Leeds, England, this PC based system uses a Rolling Horizon Optimization technique. It is economic to implement in a small town with as little as three or four intersections and is scalable into a large city system. The system uses an industrial grade single board PC card which can be installed in a wide range of existing traffic signal controllers. The card takes control of the unit and communicates with neighbouring control units upstream and downstream of its location.
Each traffic light controller becomes a node in a local area network, with TCP/IP capability. Data is exchanged with neighbouring intersections every 3 seconds and optimization is constantly performed over a rolling horizon 2 minute time frame. Public transport and emergency vehicle priority is supported, without sacrificing adaptive performance. Public transport priority operates on a selective priority basis - ie only vehicles running behind schedule receive priority at signalised intersections.
The UPOPIA / SPOT system has delivered increases of up to 35% in public transport speeds and 30% in private vehicle traffic speeds, when compared with fixed time signal systems.
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