Transport for London is to run a six-month trial of vehicles fitted with automatic speed limiters.

The trials are in advance of the intelligent speed adaptation (ISA) technology coming to market.

Chris Lines, head of TfL's London Road Safety Unit, said the technology, which can automatically prevent a driver from exceeding the speed limit, will reduce road casualties and help drivers avoid speeding penalties.

Twenty TfL vehicles will be fitted with the ISA devices, which allow drivers to select between an advisory warning or the automatic option where acceleration is stopped at the speed limit specific to any road in London within the M25 area.

The technology uses the digital speed limit map of London which TfL launched on January 29, 2009.

This is the first time all of London's speed limits have been mapped accurately with regular updates.

Drivers also have the option to disable the system entirely.

Following the trial a report will be submitted to the Mayor of London, and the technology will be made available to external organisations.

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

The trial will also allow TfL to monitor driver behaviour, journey times and the effect that driving within the speed limit has on vehicle emissions.

TfL said if two thirds of London drivers use the ISA system, the number of road casualties in the capital could be reduced by 10%.

“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,” said Lines.

"We know the technology works, and now we want to know how drivers in all types of vehicles respond to it.

“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.”

Councillor Jeff Hook, executive member for environment at Southwark Council, said: “This technology could revolutionise the way we keep our roads safer in Southwark, and that's why we're really interested in this trial, and if it's successful we hope to kit out our entire fleet of nearly 300 vehicles as soon as funding allows.”

However, Andrew Howard, head of road safety at the AA, offered a word of caution: 'Drivers are divided in their views of intelligent speed adaptation - some hate it, some want it,” he said.