The speed limit will be reduced to 60mph on four stretches of English motorway in an effort to reduce air pollution.

Highways England is set to introduce the trial by the end of September to improve roadside air quality. The move targets areas which have been identified as having high levels of nitrogen dioxide (NO2) from car engines.

The four locations where trial will take place are the M6 junctions 6 to 7 (near Witton), M1 junctions 34 to 33 (near Rotherham), M602 junctions 1 to 3 (near Eccles) and the M5 junctions 1 to 2 (near Oldbury).

Each locations is up to 4.5 miles long and the new speed limits will be operational 24 hours a day 7 Days a week. The reduced speed limits will be assessed after 12 months to see if they are having an impact, or if the air quality level is compliant.

Highways England, the government-owned company responsible for maintaining England’s motorways, said in a statement: “Emissions limits are measured on annual average figures and so the restrictions will be in place around the clock in order to improve air quality.”

The company has said it is committed to meeting the targets in the government’s NO2 plan, which aims to reduce roadside nitrogen dioxide concentrations. Its research suggests there will be a reduction in NO2 when traffic speed is reduced from 70mph to 60mph.

Ivan Le Fevre, head of environment at Highways England, said: “We have a duty to tackle air quality around our network and as part of this we are trialling 60mph speed limits on short sections of our network where action needs to be taken.

“Ultimately the air quality challenge will be solved ‘at the tailpipe’ by vehicle manufacturers and changes in vehicle use. Until this happens we will continue our extensive programme of pioneering research and solutions.

“The speed limits trial will stay in place until the shift to cleaner vehicles means we can remove the restrictions and maintain cleaner air.”