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Automatic recording of traffic data with PTB-tested light barrier


Reliable and highly detailed information on traffic is becoming increasingly needed in order to make decisions in traffic, urban and environmental planning. For this, automatic systems are optimal. A large number of various recording systems is commercially available to acquire the required data. The advantages and disadvantages of the measurement principles used in these detection and recording systems are, however, often not sufficiently known by the persons in charge of these tasks. PTB has been involved in a project of the Forschungsgesellschaft für Straßen- und Verkehrswesen (FGSV – Road and traffic research group) in order to help the persons in charge of such tasks select appropriate detection and recording systems.

For this purpose, experts from different fields (besides PTB, also the Federal Highway Research Institute (BASt – Bundesanstalt für Straßenwesen), universities, engineering and planning consultants, urban planning agencies, and manufacturers) have compiled a qualified, manufacturer-independent and extensive publication [1].
This publication contains guidance concerning the possible detection and recording systems with regard to:
- the technical functional principle;
- the detectable parameters;
- the possibilities and limits of use;
- the preparation and realisation of the measurements;
- special guidance concerning the treatment and analysis of the data;
- the estimated costs;
- a bibliography for each category of instruments.

Which functional principle is best adapted to a concrete usage primarily depends on the parameters to be detected. The publication is limited to the most relevant instruments in daily practice which enable a short-term and, as far as possible, fully automatic detection, recording and analysis of collective traffic data. "Short-term" in this context can mean recordings of a few hours and up to several weeks or even months, but also repeat measurements in the same place.

Fig. 1: One-side sensor ES3.0, equipped with multiple light barrier (Source: Manufacturer eso).

The speed-measuring instruments approved by PTB for verification hereby play a particular role. For the approved types which are normally used in official traffic monitoring, PTB's testing ensures that the legally prescribed, well-defined maximum permissible errors are complied with. Figure 2 shows a light barrier of the type ES 3.0 (manufacturer: eso) that has been granted type approval by PTB. This system is equipped with statistic functions by means of which the histogram shown in Figure 3 has been generated. This histogram provides information on the distribution of the speed of the vehicles driving on a federal motorway without speed limit.

Fig. 2: Multiple light barrier ES 3.0 (source: manufacturer eso): the sensor probe is equipped with 5 passive optical sensors. Three of these sensors are arranged in a right angle to the road and are used to measure the speed of the vehicles; two other sensors are arranged diagonally by ±0,4° and are used to determine the lateral distance between the vehicle and the sensor. Thanks to this system, it is possible to clearly attribute a speed value to each vehicle when several vehicles pass the point of measurement simultaneously.

Fig. 3: Histogram of the distribution of the vehicles' speed


[1] Hinweise zur kurzzeitigen automatischen Erfassung von Daten des Straßenverkehrs, FGSV Verlag 2010 [in German]

Contact person:

Frank Märtens, Dept. 1.3, WG 1.31, E-Mail: frank.maertens@ptb.de