By Mark Stillman
Driving groups fear that motorway speed limits could eventually be reduced nationwide, following new proposals for a 60mph stretch on the M1.
The Highways Agency published plans for the speed restriction along 34 miles (54.7km) of the M1.
The ceiling would affect drivers between junction 28 at Mansfield and junction 35a for Sheffield and Rotherham from 7am and 7pm, seven days a week in a move to help lower emissions along the stretch.
Impact on air quality
But the RAC believes the cut could open the door for comparable speed limits on other parts of motorway.
The planned reduction is part of the "smart motorway" initiative, which would see the hard shoulder being employed as an additional lane to smooth congestion.
Environmental tests undertaken on the planned 60mph M1 stretch 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 Agency claimed.
A consultation on the plan will finish on March 3, with construction of the smart motorway scheme due to begin this spring.
'Negative impact on business efficiency'
David Bizley, RAC technical director, said: "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.
"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."
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."