Motoring campaigners have warned that speed limits on motorways across the country could be cut after the Highways Agency announced plans for a 60mph zone on the M1.
The plan would come into effect between junction 28 of the M1 at Mansfield and junction 35a for Sheffield and Rotherham between 7am and 7pm, seven days a week.
The Highways Agency said the reduced speed limit would be used to help reduce emissions along the route.
But the RAC said the move could pave the way for similar speed restrictions on other sections of motorway.
The proposed reduction is part of the "smart motorway" scheme, which would involve the hard shoulder being used as an extra lane to ease congestion.
Environmental assessments carried out on the proposed scheme on the section of the M1 showed there was "likely to be an adverse impact on local air quality if the motorway continued to operate at the national speed limit", the Highways Agency said.
A consultation on the proposed speed reduction will run until March 3, with construction of the smart motorway scheme scheduled to start in the spring.
RAC technical director David Bizley said: "This is a landmark proposal as to the best of our knowledge motorway speed limits have not previously been lowered in order to comply with environmental legislation.
"If this becomes reality for the 34-mile stretch of the M1, which seems highly likely, it would certainly negate some of the current benefits of operating this section as a 'smart' motorway where motorists are allowed to use the hard shoulder to reduce congestion.
"More worryingly, it could pave the way for similar restrictions on other sections of motorway. While preserving air quality is obviously a paramount concern there will inevitably be a negative impact on business efficiency and individual mobility.
"This very powerfully demonstrates the impact that speed has on emissions and many will be surprised to hear that a reduction of just 10mph can have such a significant effect on improving air quality."
He added: " Perhaps the Government should be considering reintroduction of incentives to scrap older high polluting vehicles to minimise the need for speed restrictions of the type proposed."
Brian MacDowall, chairman of campaign group the Alliance of British Drivers, said: "Motorways are the main transport arteries of the nation and are vital to the economy.
"The Government should be raising motorway speed limits, not reducing them. Air quality is important, but it has improved massively in recent years and will continue to do so, as newer, cleaner vehicles replace older ones.
"The EU's air quality targets must not be used as an excuse to reduce speed limits or abandon vital road improvement schemes. If this proposal goes ahead, it will be the thin end of a very large wedge. It should be scrapped immediately."
Roads Minister Robert Goodwill said: "No decision has been taken to impose speed restrictions on the M1. Any speed restrictions to improve air quality would be temporary, only ever considered as part of road improvement work and would not be appropriate for the vast majority of projects started in this Parliament.
"We are funding significant improvements to the road network to tackle congestion and support the economy. Smart motorways mean more lanes for drivers, freer-flowing traffic and quicker journeys.
"We need to ensure that, as we invest, we are alive to instances where there could be a negative effect on air quality."
AA president Edmund King said: "As there are plans for more than 100 miles of hard shoulder running on motorways, the AA is concerned that these proposals may introduce a 60mph limit on motorways by the back door.
"Billions spent on railways to speed up thousands of journeys while hundreds of millions spent on the M1 to slow down hundreds of thousands is an irony that won't be lost on drivers."
He went on: "In our polls the vast majority of our members tell us that, when they change their cars, they will go for cleaner and more fuel-efficient ones because of the obvious benefit to their pockets and the environment.
"A large percentage of them will have spent extra money on diesel cars with the latest exhaust technology to cut CO2 and other emissions. Their reward: slower journeys and a greater threat of fines. We clearly have more to do to improve pollutants from larger vehicles."