Motorway speed limits are to be cut to 60mph on four stretches of road in a trial aimed at cutting air pollution from cars.
The trial is being introduced in four locations which have been identified as having high levels of nitrogen dioxide.
Nitrogen dioxide is one of the pollutants put out by combustion engines and is known to irritate the airways in humans, worsen symptoms for those with respiratory diseases and indirectly contributes to global warming.
The four sites where the trial will take place are all controlled by Highways England, which said the scheme would begin by the end of September.
The locations are between 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 trial area will cover up to four and a half miles of motorway and the new limit will apply 24 hours a day.
Highways England said the lower limit will be in place 24 hours a day and it would review the impact of the change after 12 months. In a statement it explained: "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."
Ivan Le Fevre, head of environment at Highways England, hinted that the trial could be extended beyond the 12-month period.
He 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."