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Travel time measuring system based on platoon matching: a field study
Published April 15, 1996 by Intelligent Transportation Systems in United States
To realize a cost-effective and high-resolution travel time measuring system, a new algorithm which uses only conventional ultrasonic detectors is developed. This algorithm consists of two parts.
As the first step, to determine vehicle type and estimate velocity using only a single ultrasonic detector, an algorithm similar to PLL (phase locked loop) is applied to pulse data obtained from each ultrasonic detector. This algorithm assumes a smooth traffic flow where two adjacent vehicles run at almost the same velocity and the variation of the pulse width is mainly caused by the variation of the size of the vehicles. Once the algorithm locks at platoon's group velocity, it gives individual vehicle velocity and size.
As the second step, after forming a time series of vehicle size at each point of detector, the new algorithm tries to find a similarity between two time series at two different points. The time lag of the similar patterns corresponds to the travel time. The time series reflects a characteristic of platoons at different observation points. As for the characteristic, local ratio of large vehicles within each platoon ins introduced. A prototype of the real-time travel time measuring system which consists of transmitters, receivers, a PC and a workstation was developed. Several experiments were conducted using two ultrasonic detectors installed 600m apart at an arterial road to evaluate the feasibility of the algorithm.
Fairly promising results of 90% accuracy in travel time were obtained both for unsaturated and congested situations