The speed limit on the stretch of the M42 near Birmingham that uses the hard shoulder during rush hours has been raised from 50mph to 60mph.
This Active Traffic Management (ATM) scheme has seen personal injury accidents fall from an average 5.1 per month to 1.8, which has also affected car insurance premiums.
Additional benefits include journey times being reduced by a quarter, journey-time predictions improved by 27%, fuel consumption reduced by 4% and vehicle emissions by 10%. The increased speed limit will apply to the whole ATM stretch between junctions 3A and 7.
Highways Agency spokesman Derek Turner said: "We are increasing the limit after a successful test demonstrated that we can improve journey times without having a negative impact on the M42's safety record.
"Safety is paramount to the operation of hard-shoulder running, and we will be closely monitoring the impact of the speed increase on both journey times and driver behaviour."
Work has recently started to extend hard shoulder running to other motorways around Birmingham. Two new stretches will be added on the M6, with variable speed limits to be used on parts of the M42 and M40.
© The Press Association 2008