<P> A report published in 2008 estimated that following the introduction of 20 mph zones in London, a reduction of casualties by 45% and KSI by 57% occurred . </P> <P> Research carried out for the Department for Transport, to provide supporting evidence for Local Transport Note 1 / 11 on shared space, showed that in all of the ten shared space sites that were studied, that although they all had speed limits of 30 mph, that the average speeds on them was around 20 mph . </P> <P> In 1966, at the end of the 4 - month trial of a blanket 70 mph (113 km / h) speed limit on previously unrestricted roads and motorways, speed checks on the M6 in Cheshire suggested that although cars were actually being driven about 10 mph (16 km / h) faster, they were still usually travelling at speeds below the new limit . The crash rate was lower on the M6 in Staffordshire (the better weather was noted too) and continued to fall on the M5 in Worcestershire as it had before the new limit was imposed, and there was no change in the crash rate on the M6 in Cheshire or on the M1 in Northamptonshire . </P> <P> Speed limit enforcement is used to check that road vehicles are complying with the speed limits . Methods used include Fixed speed cameras, Average speed cameras and also police operated LIDAR speed guns and older radar speed guns . In addition Vehicle activated sign and Community Speed Watch groups also encourage compliance . For lower speed limits, physical Traffic Calming is normally required . Fixed speed cameras are controversial with various advocacy groups supporting and opposing their use . </P>

What is the speed limit on the m5