Abstract: A vehicle position determination system for determining the position of a moving vehicle having a transponder includes a first and second antennas operable to receive periodic radio frequency data signals from the transponder when the transponder is moving through a first or second predetermined coverage zone, respectively. The first and second coverage zones partially overlap and each have a width that is orthogonal to the travel path of the moving vehicle and a length that is parallel to the travel path of the moving vehicle. A processor counts the number of periodic data signals received by each of the antennas from the transponder during a time period and determines based on the count a probable location of the vehicle. The vehicle location information can be provided to an imaging system to discriminate between transponder and non-transponder equipped vehicles.

Abstract: Traffic management or enforcement is performed through the use of a monitor transponder in the environs of an RF highway toll collection system. When normally operating transponders communicate with a roadside reader system, the roadside system communicates with the monitor transponder, which in turn signals if a valid normal transponder is detected. If no signal is generated by the monitor transponder, it is evident that the vehicle has no transponder or that the transponder is faulty or invalid.