The Personnel Warning System: Improving the Safety of Road Workers
T Sachse, Siemens AG; H-A Gabriel, Nissen Elekrtobau GmbH;
One of the results of the increasing traffic volume on our highways are collisions between lorries or trucks and safety barriers of road works. These collisions are generally attributable to fatigue or carelessness of the driver. Due to the heavy weight of the trucks the safety barrier is moved after the crash towards the working persons until it comes finally to a stop. To prevent the working personnel of these dangerous situations a system has been built up which detects the approaching vehicle via a laser beam, it measures the driving parameters and calculates the accident probability. If the probability is high enough the personnel is warned by an audible and visible signal.
The laser detector operates by measuring the time taken for invisible laser pulses to travel to the target and back again. This process uses diffuse or directional backscatter of the laser pulses from the surface of the target.
A microcomputer inside the unit periodically activates a diode laser. During the measurement period, a series of extremely short infrared light pulses are emitted; these are focused by the transmitter optics, emitted as a laser beam and reflected by the target. An analyser unit measures the time interval between the send and receive pulses, which is an indication of the distance from the target.
The microcomputer stores and further processes the individual measured values.The speed of the target is calculated from the change in distance during the measurement period. All themeasurement points for calculating speed are included using the regression method. The distance sequence is then subjected to a plausibility check based on several criteria. If one of the criteria is not satisfied, an error message to this effect is displayed instead of a speed. The distance measured is displayed irrespective of this for each target acquired within the range. The acceleration of the target vehicle is also calculated from the changes in speed in a succession of measurement intervals. The measured values are analysed and interpreted using the fuzzy technique. The result yielded by this interpretation is the probability of collision. This collision probability is converted into an audible signal emitted at the safety vehicle itself and at one or more mobile warning units. The type of audible signals depends on the probability of collision. With low probability, a series of warning tones are generated. The interval between the warning tones becomes shorter as the probability of collision increases, until a continuous tone is sounded indicating the greatest probability (= danger).
To address the driver of the approaching vehicle a signal warns him when he is still 100 meters away from the obstacle. The system has been tested in cooperation with different motorway surveillance centers in Germany. The paper describes the construction of the system, the fuzzy decision principle and results and experiences of field trials on motorways in Germany.
Association for European Transport