Telemetry apparatus for recoding the paths taken by vehicles on a road or rail network

A mobile telemetry apparatus is provided for use in a vehicle travelling on a road or rail network. The apparatus comprises a processor, and a data storage unit containing a map database. The apparatus is configured to store in a long term storage unit, or to transmit to an external back-office system, output data representative of the most likely path travelled by the vehicle on a map of the network represented in the map database. The processor is programmed to respond to an input identifying the known position of the vehicle at two fixed locations on the map at different known times to determine all possible paths on the map between those fixed locations taking account of the known times. From the possible paths the processor determines the most likely path to have been taken. The apparatus is particularly suited to identify the path taken by a vehicle whilst operating at a lower position sampling frequency such that it may avoid the higher costs associated with frequently sending position data to an external system.