Portable Roadside Sensors for Vehicle Counting and Speed Measurement

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This paper reports on the testing of a portable roadside sensor system for measurement of traffic flow rate, vehicle speeds, and vehicle classification. The sensor system consists of wireless anisotropic magnetic devices that are placed next to the roadway to measure traffic in the immediately adjacent lane. The vehicle detection algorithm is based on thresholds, and speed measurement is based on calculation of cross-correlation between longitudinally spaced sensors. The calculation of vehicle length follows from using a combination of vehicle speed and vehicle occupancy measurements. Rejection of data from vehicles in non-adjacent lanes is done by using model based position analysis of the magnetic field of vehicles. Data are presented from a large number of vehicles on a regular busy urban road in the Twin Cities in Minnesota. An accurate GPS was used to measure vehicle reference speeds to evaluate the accuracy of the speed measurement from the new sensor system.

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.
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Saber Taghvaeeyan, Rajesh Rajamani
Transportation Research Board