"Transport for London (TfL), which will today announce a six-month trial of ISA, estimates that, if two thirds of London drivers used the devices, the number of road casualties in the capital could be reduced by 10 per cent."
Most cars in London don't actually move fast enough to get to 20Mph, so how exactly would this system save lives?
Most UK private cars have had their speedometer set 10% fast anyway (reads 33 when doing 30 and 77 when doing 70) in an effort to both slow you down and remove te vehicle manufacturer from any possible law suits regarding speeding fines.