Average speed cameras are being fitted on the A3 at Esher as it nears the Hook underpass.
Highways England are replacing the fixed "safety spot" 50mph cameras where the northbound carriageway narrows from three lanes to two.
The large boxed cameras have been in place since 1995, but a spokesman from the roads agency said they were replacing them with the average speed markers for safety purposes.
He added that the current cameras use outdated wet film technology which is no longer supported.
The maximum speed of the carriageway leading to Tolworth and New Malden will remain at 50mph.
A Highways England spokesperson said:“Safety is our top priority and we’ve always been clear that speed cameras make journeys safer and reducing dangerous driving.
“The Esher Bypass forms an important element between London and Portsmouth. It is important that we do all we can to keep traffic on it flowing smoothly to improve journeys for motorists.
“The cameras will help to more effectively reduce the risk of accidents and also reduce stop-start congestion as well as help improve air quality.”