More speed cameras and improved junctions are essential to the plan to upgrade the A38 to motorway standard, according to a senior roads expert.
But the £1bn strategy could cut off tiny communities between Plymouth and Exeter forever because 'farm-track' style roads connecting them to the dual carriageway would never comply with motorway regulations.
University of Plymouth traffic Professor Jon Shaw believes the package of measures would drastically improve overall safety, accident rates and curb irresponsible and dangerous driving.
Prof Shaw has also called for an entire re-work of the A38 west of Exeter around Haldon Hill as part of the masterplan to bring the M5 south of Exeter and down to the Tamar.
He said: "An active way of reducing accidents on the A38 would be to bring about a raft of improvements, and in certain places, install more average speed cameras.
"One of the reasons why motorways are safer than other roads is because they are straighter and wider and the curves are less dangerous.
"They are generally better engineered roads.
"If the A38 is to be turned into a motorway, the western side of Haldon Hill would need to be completely re-engineered.
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"The twisty part going up to Exeter, you couldn't have that on a motorway.
"You would also have to look at accident black-spots on the road, and it may mean introducing average speed check cameras along a stretch of road.
"By putting in average speed check cameras in certain locations, the accident rate could go down by 95 per cent.
Prof Shaw's junctions/routes that would need to be axed or 're-engineered'
The junction off Buckfastleigh/near the Well Hung Meat Company
Prof Shaw believes 'farm-track' style road junctions wouldn't be able to exist if the 'M38' were to be rolled out.
He said: "Lots of junctions would be closed, particularly ones which are effectively farm tracks, because it wouldn't be safe to use them. They wouldn't be compliant with motorway regulations."
He said the plans would be of benefit to Plymouth - but not necessary to '100 people who live in places like Rattery'.
Haldon Hill: The link between the A38 and the A380
Prof Shaw believes the t-style junction linking the A39 and the A380 at Haldon Hill is too dangerous and wouldn't meet motorway standards.
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He said: "That section would have to be completely re-engineered and massively rebuilt.
"On a motorway you can't have traffic having to go from 0 to 70mph."
Deep Lane: Saved
Prof Shaw believes modernisation works carried out at the A38 Deep Lane junction would see it stay as part of a motorway network.
He says that changes widening the Newton Abbot junction make it strong and safe enough.
Why a Plymouth motorway won't solve everything
A motorway to Plymouth would help to put the city on the map - but unless it comes with a whole raft of improvements then prospects won't change.
That's the view of Prof Shaw - and whilst he backs the campaign being led by the likes of Plymouth MP Luke Pollard for cash to upgrade the A38 - he thinks there needs to be money set aside for better rail links too.
And tax relief 'zones' for businesses would also attract more companies to set up shop, he feels.
Prof Shaw said: "A transport investment in itself isn't going to be the key to economic success.
"In an ideal world, the motorway would be great, because it would be one part of a broader economic development strategy which would show business what is happening in the region more broadly.
"We would need a sweep of economic policies in place, not just a motorway."
The campaign: What we know so far
The motorway aspirations could come as part of a deal being presented to the government for greater powers, more money and greater control over local decisions - otherwise known as devolution.
Plymouth city council boss Ian Bowyer has said he wants the government to 'put its money where its mouth is' and stump up the money to bring the blue lines to the city.
He's been backed by Labour MP Luke Pollard, wheras Tory counterpart Johnny Mercer has said he believes it's a load of 'hot air' and not realistic.
The council is due to carry out a consultation with the public later this month over its devolution strategy. It will give the people the opportunity to decide what powers they want brought down from the government which could improve their everyday lives.
It could mean the council having greater control over housing numbers, schooling and health strategy and which roads need built to ease congestion and attract more business.