Bridge weigh-in-motion system

Abstract

An apparatus and method are provided for calculating the speed and weight of a vehicle as it passes over an existing bridge. The apparatus includes a number of strain gages attachable to existing bridge girders or support members each of which outputs an analog strain signal in response to strain sustained by the bridge when a vehicle passes thereover. An analog front end circuit card amplifies the analog strain signal and converts it into digital format. A pair of axle sensors installed in or on the pavement before the bridge each output an axle sense signal in response to a vehicle axle passing thereover. A central processing unit receives the axle sense signals and the digitally formatted strain signals and performs calculations necessary to determine vehicle speed and weight. A static random access memory card is used to retain the results of these calculations for retrieval at a later time. A power supply provides electrical power to the system components. The method comprises the steps of providing axle sense signals generated by a pair of axle sensors in response to a vehicle passing thereover, providing an analog strain signal generated by a strain gage attached to a bridge structure, converting the analog strain signal to digital format, determining the vehicle speed and axle spacings, relating the position of every axle on the bridge to the strain record, and calculating axle weights using a least squares error minimization algorithm.