Britain's first pollution-related speed limits of 60mph during the rush hour could be imposed on the M1.
Highways England is considering imposing the restrictions near Sheffield, where the M1 runs close to homes and schools, The Sunday Times reports.
The limits would come into effect from March, when the Department for Transport plans to open a "smart" motorway by converting the hard shoulder into a fourth lane, adding 5,000 to 10,000 vehicles to the 130,000 already using the road each day.
Highways England reports warned the increase will expose nearby residents to even worse pollution, potentially making the scheme illegal.
A report by engineering company Mouchel said the best way to prevent an increase in illegal pollution would be a speed limit of 60mph during the rush hour.
Nick Harris, Highways England's operations director, wrote to local MPs last month to say: “The published air quality mitigation for this scheme envisages 60mph speed limits in the weekday morning [7-9am] and evening [3-7pm] between junctions 28-35a.
"We are looking into initiatives that might avoid or reduce the need for these speed limits.”
A spokesman for the Department for Transport told The Sunday Times: "The Government will update... plans for 2017 to improve air quality."
They did not provide any further details.
