Drivers are being warned to take their foot off the gas on the Forth Road Bridge when average speed cameras go live southbound on Thursday (January 14).
The safety cameras have been in action on the northbound section of the A90 since last September, enforcing a reduced 40mph speed limit.
They will now be force on the carriageways in both directions until roadworks are scheduled to finish at the end of December.
The new section extends from Admirality to Scotstoun.
On the approach and throughout the roadworks, signs will advise drivers of the speed restrictions.
The cameras are part of increased safety measures for both workers and the travelling public while work takes place next to the mainline A90.
This work is a part of a significant upgrade to the road network tied in with the construction of the Queensferry Crossing.
Steven Brown, Transport Scotland roads & infrastructure manager, said: “When switching on the northbound cameras last year we indicated that southbound average speed cameras would be installed for use when required.
“With the progress being made on the A90 road upgrade and the shifting focus of the work, operations are now within close proximity to live traffic travelling in both directions on the A90.
“This means it is now time to switch the average speed camera system on and enforce the reduction of the speed limit to 40 mph both northbound and southbound in the area.
“The safety of our workforce and the travelling public is of paramount importance and the cameras will encourage a safe and steady flow of traffic through the works area.
“Our experience of major road upgrades has shown safety cameras are a reliable way to improve safety for both road users and construction workers.
“We have been impressed with the levels of compliance with the 40mph speed limit since it was introduced on the A90 northbound in September last year.
“The cameras will remain in place until the project is complete in December 2016.”
The bridge was closed to all traffic on December 4 after a crack was discovered in a truss under the carriageway. It reopened to all vehicles except HGVs on December 23 after repairs were carried out.