Abstract: An onboard unit consisting of a tape recorder, and associated data handling components utilized to provide records of vehicular operating information including speed, distance, power level, braking level, traction motor current and other control events. Each quantity is associated with an incremental distance and/or time which is fixed. In the case of a rail guided vehicle, location signals provided by ground mounted markers are also recorded. Summation of incremental distances as determined from each marker provides an exact location. A magnetic tape unit provides both data storage and operations instruction for a microprocessor based system, allowing convenient alteration or variations in unit function without internal modification. Each unit retains a unique non-volatile serial number which is transferred to each tape allowing convenient correlation of recorded tapes to onboard units.