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.