UK transport agencies should install average speed cameras on all the country’s motorways to cut speed and reduce carbon dioxide (CO2) emissions, an independent watchdog said.

A CO2 emission cut of 1.4 million tons could be achieved by reinforcing a 70mph speed limit with average speed cameras, according to a report by the Sustainable Development Commission.

Department for Transport figures have shown that the 70mph speed limit is being ignored by 52% of motorists.

The cameras measure the time between a vehicle entering and leaving the zone and calculate if the driver exceeded the average speed limit by knowing the shortest route between the entry and exit points.

The dangerous instances of sudden braking, which occurs with traditional fixed cameras, are also avoided.