From the bbc site.
Speed-limiting devices should be fitted to cars on a voluntary basis to help save lives and cut carbon emissions, according to a new report.
The government's transport advisers claim the technology would cut road accidents with injuries by 29%.
The device automatically slows a car down to within the limit for the road on which it is being driven.
Ministers are planning to help councils draw up digital maps with details of the legal speed on every road.
The system uses satellite positioning to check its location and when the speed exceeds the limit, power is reduced and the brakes are applied if necessary.
It has been well-trialled, and the Commission for Integrated Transport and the Motorists' Forum, which both advise the government, are calling on ministers to promote a wide introduction of the system.
The advisers believe it should be voluntary but say drivers who have tried it, liked not having to worry about exceeding the limit.
However, the BBC's transport correspondent Tom Symonds said the report is likely to be rejected by some motoring groups which believe the government overestimates the importance of speed in causing accidents.