Abstract
A new method of vehicular speed measurement is presented. The principle is to determine the transit time, whicn is required for two points on a motor vehicle to pass over a point on a road surface. Two optical detectors are mounted on a moter vehicle in line, in the vehicle direction. Random signals are obtained from the road surface by the detectors. The relative delay between the signals is determined from their coincidence, by shifting one of them, or from the peak of their cross-correlation function.
The measurement is capable of very high accuracy.
Errors of the speed measurements are studied in detail: The resolution of the delay determination from a single cross-correlation function depends on the sampling interval of the random signals. Statistical error of the measured speed depends on (1) the aperture diameters of the detecters, (2) SNR of the signals and (3) the averaging length required to obtain the crosscorrelation functions. The vehicular speed can be determined to an accuracy of 0.7%, for instance, using rectangular apertures of 6×30mm and an averaging length of 2.20m.
Advantages over the conventional methods and shortcomings of the new method are described.
