Road lighting is to be turned off on a section of motorway near Exeter overnight as part of plans to save money and reduce carbon emissions.
From mid-April, lights will be switched off between midnight and 0500 GMT between junctions 29 and 30 on the M5.
Critics have raised concerns about road safety if lights are turned off.
The Highways Agency said it was not a dangerous move and added it would cut 40 tonnes of carbon a year, as well as reduce electricity costs by £8,000.
East Devon MP Hugo Swire said he was concerned about safety and would raise the issue with the Highways Agency.
Graham Bowskill, from the agency, said that lights on junction slip roads would remain on.
He said: "Work that we've done shows there is a much lower link between street-lighting and safety on motorways.
"Motorways are our safest roads anyway. They're long, straight roads and those areas that benefit most from lighting, road junctions for example, we're not proposing to turn the lights off at all."
The move has also been welcomed by the Institute of Advanced Motorists because it "targeted the safest and quietest motorways".
The institute's director of policy and research, Neil Greig, said: "We were concerned that a rush to reduce the carbon footprint of motorway lighting might have led to safety taking a back seat.
"But the Highways Agency has struck the right balance by continuing to illuminate junctions and opting for low flow routes with a good road safety record."