Raising the motorway speed limit to 80mph will cost society an extra £1bn a year, campaign groups have claimed.
The cost includes £766m in fuel bills and more than £62m in health costs, the groups said.
It is also estimated that the higher limit will lead to 25 extra deaths and 100 serious injuries a year, as well as 2.2 million more tonnes of carbon emissions.
The Government is due to consult soon on raising the speed limit from 70mph to 80mph on English and Welsh motorways.
The groups, which include road safety charity Brake, the Campaign for Better Transport (CBT) and Greenpeace, yesterday launched a campaign – called No to 80 – protesting at the Government’s plans.
The groups reckon an 80mph limit would result in extra annual costs of:
£62.4m from road casualties, including costs to health and emergency services and human costs;
£180.4m in carbon costs;
£766.6m in fuel costs.
The groups are writing to Transport Secretary Justine Greening to request a meeting “reviewing the evidence against 80mph limits”.
Brake deputy chief executive Julie Townsend said: “The No to 80 campaign calls on the Government to listen to the overwhelming evidence that raising motorway limits is dangerous, costly and damaging.
“Experts predict it would lead to more lives being brutally cut short and more people suffering debilitating injuries. At the same time, the economic argument being used to defend the proposal does not stand up to scrutiny and the average driver will gain little to nothing in journey time savings.”
CBT campaigns director Richard Hebditch said: “There is no compelling case for increasing motorway speed limits to 80mph. While the Treasury might benefit from more fuel duty revenue as drivers used more petrol, for ordinary motorists it would just make for a more dangerous and more polluting journey. Any change to speed limits must support moves to cut collisions and carbon, not add to them.”
Roads Minister Mike Penning said: “We plan to bring forward detailed proposals and start consultation during the next few months.”