Tachograph instruments are mounted into large goods vehicles and act as the speedometer. They also monitor the distances travelled and the speeds attained by the vehicle. The purpose of a tachograph is to record Driver's Hours; however, this information can be used to determine the speed of a vehicle on the approach to a collision, find the route taken by a vehicle and identify the locations of any stops made during a journey. There are two types of tachograph installations fitted to vehicle:

The tachograph records vehicle movements on circular paper charts inserted into the unit. The chart rotates once over a 24 hour period while information is recorded on the surface by stylii. This information includes the vehicle's speeds, distance travelled and driver activity (which can be set manually). The recordings can be analysed using a specialist microscope and the information used to identify the route taken by a vehicle (route tracing) or determine a vehicle's speed on the approach to a collision.

The digital tachograph unit records basic data, such as the times of driving and distances travelled, together with a second by second record of speed. The speed recordings enable the precise breakdown of the vehicle's movements, allowing a vehicle's route to be traced and its speeds leading up to a collision determined. The detailed speed data is held within the the memory of the digital tachograph and has to be downloaded by a trained enforcement officer or other authorised personnel. For advice about this, please contact us (before moving the vehicle, if possible). Other information is recorded within the tachograph unit and on the driver's card, which could assist an investigation.