Satnav that tells you not to break the speed limit

Transport for London is drawing up a digital map of the capital, complete with information about the maximum speed allowed on every street within the M25.

Drivers will be invited to download the map on to their satnavs.

The system could be a boon for people who have received speeding tickets after driving too fast accidentally, particularly as the capital's network of speed cameras is being increased.

Chris Lines, TfL's road safety chief, told a group of MPs that work on the system was well-advanced and could dramatically reduce the number of people injured in road accidents.

"Casualties are very much linked to speed, both numbers and severity of casualties," he told the Commons transport select committee, which is examining the issue of road safety.

Mr Lines said he believed many drivers would volunteer to use the intelligent speed adaptation technology.

He told the MPs: "There is a definite role there to be played by having vehicles which actually keep to the speed limit and perhaps longer term we can use vehicle technology to actually manage speed."

However, some experts are concerned that using ISA could make drivers more careless as they could rely on it to keep them safe. Scientists are working on another version of the technology which would actually prevent cars going any faster than the speed limit.

TfL will test the system using 10 of its own vans and cars. The drivers would be able to disable the system by switching it off, but while it was running their vehicles would obey speed limits.

Mr Lines told the committee that the system also meant that vehicles using it ran more efficiently.

"There are benefits in terms of fuel consumption, there are benefits in terms of emissions, so it is possible that some people might be happy to use it," he said.

"Tests abroad and in Europe have shown that people actually quite like using it after a while and would voluntarily fit it."

Sheila Rainger of the RAC Foundation said any device that helped drivers keep to the speed limit could be valuable. "But we don't back any system which takes control away from the driver," she said.

Former mayor Ken Livingstone supported ISA but it is not yet clear whether his successor Boris Johnson will want to devote similar resources to it.