Work is starting on a £250,000 scheme to improve safety along a stretch of the A38 near Exeter.
Highways England is installing average speed checks along the stretch at Splatford Split where the road merges with the A380.
The road saw an average of one accident a month between 2009 and 2014.
The move has been supported by Devon and Cornwall Police and Devon County Council. There will be two weeks of overnight closures.
Motorists hoping to get an early start on the Bank Holiday are being warned to avoid the A38 near Splatford Split.
The usually busy road is blocked with 11 miles of queuing traffic after a smash which saw a car collide with the central reservation.
The incident involved one car, which crashed into the central reservation on the A38 northbound.
The collision is said to be affecting journeys heading towards Exeter and the M5.
While investigations continue on the A38 at Haldon Hill, near Chudleigh, police are urging drivers to follow these diversions:
- Eastbound traffic is asked to follow the solid black diamond diversion symbols.
- Westbound traffic to asked to follow the solid black circle diversion symbols.
- Large vehicles are being advised to divert via A382 and A380 via Newton Abbot and Splatford Split.
The A38 is blocked in both directions after a lorry got stuck under a railway bridge near Trerulefoot in Cornwall.
Both sides of the roads are blocked and traffic is queueing between the B3249 and the Trerulefoot Roundabout - congestion is backed all the way up to Horningtops and Landrake.
There's been traffic chaos on the A38 near Plymouth this evening after a large oil spill closed both lanes on the Northbound.
Police are working hard to clear the spillage - which is 500m long.
The delays have caused lots of frustration for commuters, with people taking to social media to vent:
We've heard of people going to great lengths this Christmas, but it seems nothing was going to stop this man from bringing the festivities home.
And, you could forgive this man if his spirit was a little dampened after his experience.
With rain pouring down the committed reveller was captured driving along the A38 complete with his oversized tree - too big to fit in the boot - and causing him to keep the top down.
The footage was captured by Nik Dodd and, after putting it on Facebook, was quickly shared around the internet.
The driver didn't look impressed as the rain and wind battered the blue Saab, soaking the driver through.
Let's just hope his family appreciated the effort...
A family have paid tribute to a 22-year-old who died in a car crash on the A38 on September 16.
Tom Demaine, from Saltash, was described as "the most generous, kind, intelligent and funny young man" by his family.
Tom studied Biomedical Sciences at Plymouth University and was a keen sailor. He sadly died after his Ford Focus crashed off the road and into trees on the A38 at Chudleigh shortly after 12.15am.
The A38 northbound is closed between Chudleigh Knighton and Kingsteignton due to a serious collision.
Emergency services were called at 3.45am after a Ford Transit van hit a tree near to the Chedleigh turn off.
Three men have been taken to hospital following the crash, with one described as sustaining serious injuries. It is believed six dogs, who were in the back of the van escaped, but have now been rounded up and are being cared for at a nearby kennels.