factsheet 08
adaptive traffic lights and monitoring
Description of the project
Implement vehicle detection to adapt green times to the actual amount of traffic. With the same detection monitoring can be started to improve traffic models.
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Refers to specific measures
RD18a.
Objectives of the project
Optimize traffic control, gaining extra capacity. Set-up a monitoring system to improve traffic modelling and research.
Dependencies
Adaptive traffic control benefits can only be realized if there is no extreme overload and the actual schedule is fit for it. So for example adaptive control can not solve the problems at K.Valdemara iela near the old town during peak hours. This is because of the extreme overload and because the actual schedule is only two phases with minimal time for the crossing phase. Then green adaption only can be green time extension at the main street which will worsen the waiting time for crossing traffic.
Design issues
There are diverse systems which can provide the detection of the presence of vehicles. Related to monitoring it is preferred to use systems which can at least count with acceptable reliability. First tests are already in progress with the counting systems on the bridges in Riga.
Already different kinds of systems have been tested in Riga. Because of diverse problems with each kind of system till now (infrared, inductive loop, video), no effective system to count vehicles in an accurate way has been found. This reflects the situation in other countries where inductive loops are still the most common detection system. Despite of the costs no other system has achieved a substantial market share.
Experiences with inductive loops in Latvia are not positive because these ask for a lot of maintenance and repair due to the different weather conditions all year round. Because of this it is recommended to use only systems with no or at least small in-street parts preferably without cables. Current developments show it is possible to detect vehicles with minor impact on road surfaces and more robustness than conventional inductive loops.
To be able to use detection it will be necessary to connect the detection systems to the controllers. It is probably possible to make adjustments in currently used controllers but that will be relatively expensive. In general it is more cost-effective to select controllers with built-in detection facilities and hardware for inclusion in a central control system. Because of this there two cost-effective ways to implement detection systems:
- wait till controllers have to be replaced due to end of economic life cycle of technical malfunctioning;
- replace current controllers with new controllers fit for detections, old controllers can be used at new intersections (or renewed intersections) where there is less need for detection or can be used as a source of spare parts.
Examples of possible use of detection are given in the third interim report.
Note: it is important to realize that investments like this alone will not solve the major traffic problems in and around Riga. The main goal should be to make better (some more capacity), more acceptable (no waiting for no reason) and safer (less accidents) controlled intersections.
Together with investments in detection at traffic lights a central control system can be implemented with monitoring capabilities. Input for this system is gained from the above-mentioned vehicle detection and additional strategic important locations (e.g. bridges and railway crossings). Additional to counting, measurements of travel times give information about the quality of traffic flow.
In the first project implementation program 2011-2017 the main focus lies on investments in new adaptive traffic controllers with vehicle detection systems and setting the basis for a central control system. Benefits of a central control system can be providing additional information to local controllers to switch green plans or green waves according to the expected traffic load. A central traffic control system also provides better information about the status of the network like earlier or later starts of rush hours, incidents or special situations which can be a reason to select a different control plan. Successful examples of such systems are SCOOT and Utopia/SPOT. Central control systems are rapidly developing. In the past these systems were sold as powerful solutions without the need for an expensive wide spread detection network. The current trend in central control systems however is they rely more and more on vehicle detection systems to organise traffic flows in a more accurate way.
The actual network without NTC is not fit for a network control system due to unequally spread traffic volumes. For extremely overloaded intersections it is more important to strongly keep control over the local situation than relying on the results of a network control system.
Measures included
1. PT priority at traffic lights
2. Upgrade of existing public transport stops
Stages (short, medium, long term)
Short termdesign study, intersection capacity calculations and traffic light controller programming, tender procedure;
Medium term after completion of the NTC there will be lesser traffic on both streets; as a result traffic light controllers probably need to be reprogrammed;
Long termmaintenance and further expanding of the system.
Side effects
Using adaptive traffic control gives opportunities for easy implementation of operational transport priority.
Cost category
Indication of costs per intersection for quick implementation:
EUR 15.000 - EUR 20.000 depending of the number of detectors and additional units. If combined with replacement of the controller additional costs can be kept lower, EUR 5.000 - 10.000 per intersection.
Investments in the first seven to ten years:
- setting up a international procurement procedure with assistance of a specialised consultant: EUR 125.000,--;
- implement vehicle detection for monitoring and adaptive control: EUR 15.000,-- - EUR 20.000,-- per intersection;
- implementation of a central control and monitoring system based on vehicle detection at traffic lights and additional travel time measurement: EUR 350.000,--;
Note: As the number of adaptive controlled intersections increases and the central control and monitoring system becomes more useful, the number of traffic engineers need to increase as well. Tasks of those engineers will be: preparing traffic control plans; traffic control maintenance (regular evaluations and parameter updates); storage and analyses of monitoring data. But also operator function at the central traffic management system.
Stakeholders involved
Riga City Council Traffic Department, Rigas Satiksme, Latvian State Roads.
Recommendations
As said before, since the experiences with some detection systems in Riga, the adequacy of detection systems in the Latvian climate is very important for the success. Therefore it is recommended to set up the procurement documents with an international traffic management expert to set the specifications for these systems in the procurement documents.