by Dominic Sacco/PA

The Department of Transport is testing new technology that makes it impossible to break the speed limit.

Drivers will test the Intelligent Speed Adaptation (ISA) technology which detects the speed limit on a road and stops the car exceeding it.

Twenty cars as well as a London bus and taxi will take part in a six-month trial scheme, Transport for London (TFL) announced.

The technology is designed for use on the M25 and can be disabled at the touch of a button.

When cancelled, the ISA reverts to an advisory status and simply displays the current legal speed limit as a driver aid.
There is also an over-ride switch which can disable the system entirely.

Do you want a speed limiter on your car? Have your say on the Auto Trader Blog

The trial will monitor driver behaviour, journey times and how driving within the speed limit affects vehicle emissions.

It’s estimated if two thirds of London drivers use the ISA system, the number of road casualties in London could be reduced by 10 per cent.

Southwark Council in south London has already expressed an interest in fitting ISA to more than 300 of its vehicles.

Chris Lines, head of TFL's road safety unit, said: “This innovative technology could help any driver in London avoid the unnecessary penalties of creeping over the speed limit, and at the same time will save lives.

“ISA is intended as a road safety device, but if Londoners embrace this technology we may well see additional benefits, including reduced congestion as a result of collisions and reduced vehicle emissions as drivers adopt a smoother driving style.”

Andrew Howard, head of road safety at the AA, said: “Drivers are divided in their views of intelligent speed adaptation – some hate it, some want it. Many have questions which will be answered only by trials like those being carried out by TFL.”