New police digital speedometer
calibration method developed
by Road Safety Support


Road Safety Support (RSS) has developed a new method for calibrating digital speedometers in police vehicles - an issue now affecting forces across the country and restricting choice when adding modern vehicles to their fleets.

Speedometers in all cars are built by the manufacturer with a positive error, ensuring they always comply with UK and European regulations throughout the lifetime of the vehicle.

Traditionally, analogue speedometers were removed from the police vehicle and adjusted to read an accurate or close to true speed, as part of the calibration process. But many modern vehicles now have digital speedometers that cannot be adjusted without compromising the vehicle, posing a great problem for police forces.

Calibrated speedometers are essential in police cars responsible for carrying out follow checks on vehicles thought to be exceeding the speed limit.

Road Safety Support, a not-for-profit company, developed the new method for calibrating digital speedometers at its ISO 17025 accredited speed laboratory.

The method involves measuring the performance of the speedometer gauge, establishing its inaccuracy and providing correction figures to the readings of that gauge, without the need for removing the speedometer.

This process is quicker and simpler than the traditional process of calibrating analogue speedometers, saving time and money while maintaining the integrity and warranty of the vehicle.

Road Safety Support can also support every calibrated device with expert witness services and back-up calibration data is retained for every vehicle tested.

The method has already been used to calibrate the digital speedometer of a South Wales Police patrol car.

When the force discovered that the Seat Leon had a digital speedometer fitted, it was feared that the car would not be fit for purpose, as there was no apparent calibration option. Early disposal of the vehicle was a consideration.

But the force was made aware of the RSS calibration method and the process was quickly carried out. The force has been driving the vehicle successfully ever since.

Inspector Gareth Morgan, of the South Wales Police Western Roads Policing Unit, said: “In my opinion, the work carried out by RSS has transformed a vehicle that, although ideally suited to the RPU role, was not fit for purpose, due to the lack of a calibrated speedometer.

“Due to the new digital type displays, our traditional solution was not an option, and we had to consider other options.

“RSS were, to my knowledge, the only company to provide a solution, and we were at the point of decommissioning an otherwise excellent vehicle.

“The RSS method is suitable for vehicles with either digital or analogue displays, it is far quicker than the previous solution and it does not require the display to be removed from the vehicle.”

Steve Callaghan, Calibration Laboratory Manager, of Road Safety Support, said: “The work we have been doing in calibrating speedmeters for Home Office Type Approval in our accredited laboratory has been developed to deliver this answer to the police that has perplexed suppliers and fleet managers.

“In developing this solution we have not only been able to calibrate the speedometer gauge, as has been done in the past; we calibrate the entire speed sensing and display in each vehicle.”

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