TRAFFIC FLOW DATA ACQUISITION USING MAGNETICLOOP VEHICLE DETECTORS.

One means of acquiring validation data for System Development Corporations digital computer simulation of traffic flow in a freeway diamond interchange will be through the use of magnetic-loop vehicle detectors. Actual interchange performance will be monitored by direct measurement of vehicle parameters count,size, and velocity, leading eventually, through the validation process, to a realistic simulation model. Techniques were developed to extend existing loop-detector capabilities, permitting direct measurement of vehicle parameters measurements were available heretofore only on a statistical basis and experiments were conducted to determine detectorsensor-loop response characteristics. A practical sensor-loop configuration, which was developed for the validation runs and tested in controlled experiments, provided an accurate picture of the over-all traffic pattern. Measurement accuracy was investigated, considering the effects of varying vehicle height and of closely following vehicles tailgating, such as might be expected in heavy traffic. Measurement errors due to tailgating were attributable to recovery-time limitations inherent in the loop-detector circuit. The techniques described can be used, employing commercial loop-detectors, for traffic applications in which it is desired to determine vehicle velocity andor size directly in addition to vehicle counting. Author