Speed limit signs should be safety advisory indicators. It is sensible to have speed limits to protect road workers and/or children, but not sensible to enforce them when no road workers are present or schools are closed. Most drivers drive to suit the conditions: people; time of day; road surface; weather; and traffic. Sometimes it is not safe to drive at the permitted speed. A 'decelerometer' device should be developed based on airbag trigger technology. When activated by a collision it would freeze at the vehicle's speed as registered by the car computer. Examination would indicate the speed. If that speed is over the speed limit it would be taken into account in the prosecution. The other hundred of thousands of cars that pass without incident will have done just that: "PASSED WITHOUT INCIDENT". Every M.O.T. test could require that a BLUE BOX (a car version of an aviation BLACK BOX) be fitted before a certificate is issued, and new cars would have one factory fitted. Civil servants could figure out the best way to ensure foreign vehicles enter the U.K. with a BLUE BOX fitted after a set date. At Police officer discretion (let's bring discretion back) 'hazardous' driving detected either by Police or observation cameras could still be regarded as a crime and put forward for prosecution whether or not it was within the permitted indicated speed limit. Bring back punishment for those who cause damage or injury, and free up the Police and the Courts for their proper mission.