Although inductive loops are a widespread and often-used technology, single inductive loops by themselves do not measure vehicle speed or provide information sufficient to determine vehicle classification. A system has been developed that uses compact, wireless, portable sensors intended to achieve highly accurate velocity estimates by measuring time delay. This paper describes the proposed system, as well as summarizes the results of an experiment conducted in Minnesota to evaluate the accuracy of the system.
In order to check the velocity estimation accuracy of the system, an experiment was conducted at MnROAD, Minnesota's Road Research Facility. The AMR sensors were placed adjacent to the lane. A Global Positioning System (GPS) device was mounted on a vehicle and its data was captured. For each test, the driver started at a distance away from the sensors, reached the desired velocity, passed in front of the sensors with constant velocity and later stopped. The GPS recorded speed was compared with velocity estimates from the AMR sensors when the cross-correlation method was applied. The researchers also tested passing vehicles on an urban street to see if their detected magnetic length was sufficient for classification.
- The error range of velocity estimation was reduced from 20 percent using conventional methods to only 3 percent using the portable sensor system. When comparing the sensor system-based estimates of velocity to the GPS calculations, the velocity estimates were found to be accurate within +/- 2 percent.
- The accuracy of vehicle detection using all of the collected urban road data was 100 percent.