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Road sensor data – Detection loops
From Wikipedia, the free encyclopedia
A detection loop is a device used to register vehicles (to detect the presence of a vehicle). They are usually placed in the entry lanes of a traffic-light-controlled intersection or used to count vehicles (to determine traffic volumes). In the case of appropriate placement of several loops (one behind the other at a certain distance) it is possible to determine the speed of passing vehicles. Detection loops are among the most common types of traffic detectors used for traffic control purposes.
Principle of operation
During the passage or presence of the vehicle on the loop, its inductance decreases and the oscillator frequency increases. If the frequency change reaches a predetermined threshold, this change is perceived as the presence of a car on the loop.
The induction loops are recessed into the road at a depth of about 120 mm. Their size and orientation are chosen according to the purpose of their use. The dimensions of the loops range from 1 to 3 m in length and 2 to 2.5 m in width (given by the width of the lane and preventing it from being affected by vehicles in the adjacent lane). To determine the length of the column, special loops can be used, which can reach 30 m. The loop itself consists of a coil with a flexible face of 1.5 to 2.5 mm². In addition, its resistance to water and heat must be ensured.
Pros and cons
The advantage of (induction) detection loops is that it is a functional and proven technology. They provide basic transport parameters (traffic intensity, occupancy, etc.) at relatively low cost. They are not affected by weather, so they also work in adverse weather conditions.
On the other hand, an inconvenience is the fact that during their application (even possible maintenance) it is necessary to close the lane and milled the asphalt layer. Malfunctions that occur are often caused by poor road surface quality. In addition, in case of road repairs, the detector is often reinstalled. Built-in detection (induction) loop reduces road life.
- Řídící jednotky MAGNETIC [online]. Praha: Profi parking [cit. 2012-10-12]. Kapitola Detekční smyčka MID1. Dostupné online.
- BUREŠ, Petr; PŘIBYL, Ondřej. Detektory zasahující do vozovky, úvod do detekce [online]. Praha: Dopravní fakulta ČVUT v Praze [cit. 2012-10-12]. Dostupné online.
Use of detection loops in Pilsen
In Pilsen, there is approximately 1000 detection loops in roads. Each loop returns intensity and occupancy values every 90s. During the year approximately 320,000,000 records is inserted in the database.
Selected detectors are combined into profiles, which are more than 300. For these profiles are then calculated aggregate hourly values of intensity and occupancy using interpolation mechanisms.
Loop data is then used to display current traffic conditions or to display historical conditions to compare situations or verify the impact of traffic measures. They are also used to calibrate the traffic model to predict traffic behavior in the future.
In the absence of ANPR data or other similar sources, it is advisable to use this data. There is no need to deal with their anonymization, but on the other hand, it is not possible to deduce from them the speed of the passage and the transit routes.
When best to use
Main data elements:
Traffic intensity and occupanycy every 90 second from each detector.