Traffic Flow Measuring System With A Laser Beam Cutting Sensor

This paper is intended as an investigation of Configu- ration of system using a laser beam cutting sensor for traffic flo\t measuremenl. The main stress falls on the development of an ap- proach for the improvement of the SKR(Laser-to-sun) in the system. Two approaches for the improvement of the SNK arc proposed. In the first one a projector which uses a prism is designed to im- prove the radial power distribution of the laser beam. In the second one a measuring system with a pulsed laser is proposed to improve the SKR. An experiment using a high speed camera was accomplished to make sure of the possibility of our approach. 1. Introduction In recent years, the increasing demand of traffic incremcnts the complexity and information to be processed by the traffic control system and the importance of traffic floir- measuring is increasing more and more. For the measuring of traffic flow in a wide area, imagc proc- essing methods have been developed, with which vehicles are de- tected by the difference of brightness between road surface and vehicle itself. In our laboratory. researches based on image processing have been carried out since 20 years ago. era, we proposed in reference (l) th:: use of a laser in the beam cutting method. The basic idea of traffic flow measuring with laser beam cut- ting method is shown in Fig.1. As is show in Fig.1, a laser and a camera are located over an arm in one ~ide of the road under measure. The radiated laser beam and the reflected beam will determine a certain angle with the normal axis of the road. The scheme of the laser radiator and its scanner is shown in Fig.2. The laser beam is widened in one direction using a cylin- drical lens. The beam forms a triangular plane like a curtain and is radiated to the road. This slit beam is reflected by the road surface or by the vehicle on the road, and is received by the camera on the arm. flected beam appears at the camera as a line when there is no car on the road, and the beam is deformed by cutting when there is a car on the road, so the shape of the reflected beam appears as is shown in Fig.3. The axis of the radiating beam and the axis of the reception bcam cross with certain angle at each position of the road surface under measure. So the beam over the car is horizon- tally slipped off from the beam over the road surface. The differ- ence between the height of the car and that of the road surface is computed by the difference of horizontal ordinates appearing in the camera. The shape pattern appearing in the camera is nearly to Based on thc development of semiconductor laser and CCD cam-