The first speed cameras targeting drivers exceeding the 70mph speed limit on a British motorway are due to be switched on along the M4.
Speed cameras will be used to enforce the speed limit on the M4
Speeding motorists on the Wiltshire section of the motorway now face £60 fines and three penalty points.
The Wiltshire Safety Camera Partnership marked vans at fixed, permanent sites, along a 40-mile stretch between Bath and Hungerford.
It says it hopes they will reduce the high number of deaths on the route.
North Wiltshire Tory candidate James Gray attacked the plans as being for Labour's "politically correct, money-making reasons".
But a Labour party spokesman said they were there to help save lives.
"I fail to see how a speed camera can be politically correct," he said.
"Speed cameras are used as one of many means to help improve road safety in communities across the country."
But Mr Gray said that if the Tories were voted into power, they would raise the speed limit on motorways to 80mph.
He said: "If speed cameras are designed to reduce accidents, then I support them.
"However if they are designed to raise revenues for the government or to be politically correct - saying 'Aren't we being good, putting up speed cameras?' - then I don't."
Saira Khan from the Wiltshire Safety Camera Partnership said that more than 200 people had died or were seriously injured on the M4 in the past year, and defended the use of the cameras.
"If those 240 people had been wiped out in one day there would have been an outcry."
"At our fixed camera sites in Wiltshire we've seen a 64% drop in personal injury collisions. If we can achieve this on the M4 it would be great," Ms Khan added.
But Paul Smith from safety campaign group Safespeed claimed the scheme would fail: "They absolutely will not work to improve road safety.
"Apart from the distraction and panic braking effects we also have to worry about moving drivers outside their 'zone of optimal performance'."
Paul Fox, the Liberal Democrats' parliamentary candidate, said speed camera laws should be enforced.
"They are a good thing because they are the one thing motorists take notice of and speed kills," he said.
Labour's parliamentary candidate for North Wiltshire is David Nash. He says hardly a week goes by without there being an accident between the two junctions.
"Bearing in mind the motorway is virtually straight the only reason for this has to be speed therefore I fully support the introduction of speed cameras on this stretch," he said.
Also running is Neil Dowdney for the UK Independence Party.