A method and system for interfacing and communicating between an in-vehicle device such as an on board diagnostic (OBD) system and an existing distance measurement instrument (DMI) are provided. In one embodiment, the interface sends a plurality of vehicle speed requests to the OBD system to obtain a plurality of vehicle speed measurements, uses the plurality of vehicle speed measurements and time stamps associated therewith to compute a distance travelled during a time interval, converts the distance travelled to a series of pulses, and sends the series of pulses to the DMI.