Evaluation of microwave radar trailers for nonintrusive traffic measurements

A trailer using two Wavetronix microwave radar units in side-fire mode was developed to measure traffic nonintrusively, including time-stamped arrival records, moving average speed (N = 16), length, and classification (0 to 20 ft, 20 to 40 ft, more than 40 ft) of each vehicle. This paper reports on an initial validation of a prototype trailer on a four-lane section of US-50 cast of Athens, Ohio. Traffic on the road was independently measured with video and radar, and the results were compared with records from the trailer to verify that the trailer was measuring the traffic with reasonable accuracy. The system records the arrival of more than 95% of all vehicles, with phantom and missed counts held to less than 5% in nearly all test cases. The overall average speed based on a 90-min time period is within 3 mph of the actual overall average values, although the observed standard deviation of the trailer moving average speed readings is about two to three times that of validation data, indicating that not all the variation is from traffic fluctuations. The vehicle classification is unreliable; the fraction of trucks in a lane call be severely overestimated or underestimated. The system needs further development to create a more reliable portable system for nonintrusive traffic measurements.