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Traffic control: Test of new detectors for traffic data acquisition

Depending on the traffic situation, different control models are used to control traffic lights or light signal systems (LSA).

Fixed-time control

The photo shows detectors for traffic data acquisition at a test junction in Nürtingen Detectors for traffic data acquisition at a test intersection in Nürtingen (Image: SWARCO TRAFFIC SYSTEMS GMBH)

The simplest type of LSA control is the fixed-time control. Here, the signal programmes run with constant circulation, release/green and blocking/red times. The circulation time is the time in which all "directions" usually get one "green" and one "red" until the signal programme has run through and starts again from the beginning. It is usually 60 to 120 seconds. The fixed time control can vary depending on the time of day, e.g. during heavy rush hour in the morning "optimised" in the direction towards the city centre and in the afternoon/evening in the direction away from the city centre.

Traffic-dependent LSA controls

However, at heavily loaded intersections or junctions, the performance of fixed-time controls reaches its limits. Dynamic, traffic-dependent LSA control systems are used here. These vary the release and closure times for the individual directions according to the current traffic volume.

Green waves

The LSA controls become even more complex in the case of "green waves" in several directions and priority for public transport, such as buses and trams (public transport prioritisation). The latter can lead to the cancellation of the clearance or to the extension of the closure times of other road users and thus to the interruption of "green waves".

Traffic-dependent LSA controls

The photo shows detectors for traffic data acquisition at a traffic light Detectors for traffic data acquisition under test (Image: SWARCO TRAFFIC SYSTEMS GMBH)

For traffic-dependent LSA controls, current traffic data is required, for example the presence of vehicles. Until now, this data has usually been measured with inductive loops laid in the roadway. The inductive loops are exposed to particularly high loads due to the many braking and starting processes at intersections and must therefore be renewed relatively frequently. This is cost-intensive and involves traffic obstructions due to necessary lane closures. In addition, inductive loops can only detect vehicles travelling over the inductive loop. Thus, spatial traffic data, such as the length of the tailback or the number of waiting vehicles, are not directly measured.

New detectors

Recently, new detectors for traffic data collection have been increasingly developed, offered and used. These can, for example, be mounted on masts above or next to the roadway and in some cases also record spatial traffic data or cyclists and pedestrians. The latter cannot be detected by inductive loops at all. The new detectors include, for example, radar, video, thermal imaging and magnetic field detectors.

Within the framework of a BASt research project, new detectors for traffic data acquisition are now being tested in Baden-Württemberg in Nürtingen (junction Oberboihinger Straße / Hochwiesenstraße/ Rümelinstraße) and their influencing variables on the quality of traffic data acquisition are being determined. This does not interfere with the control of the traffic lights. No data relevant to data protection, such as number plates, is recorded.