A series of temporary speed cameras are enforcing a 50mph speed limit on one of the main routes into Exeter.
And drivers have been warned that they are likely to stay in force for six months.
The imposing, bright yellow average speed cameras have been set up near Haldon Hill on the A38 approach into Exeter.
Work on a £9.3 million scheme to provide an extra lane to ease congestion at one of Devon's busiest junctions has just got underway.
The work, at Splatford, near Exeter, is part of the Government's Pinch Point Programme and will extend the existing two lanes of the A380 to the junction with the A38 and continue to the Wobbly Wheel junction. It is due to be completed in March 2015.
The initial work, until the end of the month, involved the installation of the bCCTV cameras and crossing points for contraflow traffic, and has taken place overnight.
During the majority of the work, five traffic lanes will be maintained with two lanes in each direction and the centre lane used to cater for peak commuter flows (eastbound in the mornings and westbound in the evenings).
The increase in capacity on the road will improve the flow of traffic through the area which suffers severe congestion and delays. It will also cater for traffic following the opening of the Kingskerswell bypass due at the end of 2015.
The Highways Agency said the temporary 50mph speed limit with average speed cameras was for the safety of road users and the workforce.
Project sponsor David Stock said: "This major investment in the A38 will reduce congestion and help economic development in the wider Exeter area.
"Drivers will benefit from reduced journey times through reduced congestion at peak times."
