Work has started to open the hard shoulder on a section of the M25 in Epping Forest to traffic.
The £188m project between junctions 23 and 27 will see emergency areas created for broken down vehicles.
The Highways Agency said extra controls will also be provided, such as CCTV cameras and signals, to allow lanes to be closed and traffic officers sent to the scene of any incident.
This particular section of the motorway, which serves the A1(M) and M11, has suffered from increasing congestion, with around 120,000 motorists using this stretch of the road each day.
The Highways Agency said converting the hard shoulder is cheaper and causes less disruption than a traditional road widening scheme.
However, there are concerns the removal of the hard shoulder will compromise road safety, with no immediate traffic-free area in which to stop if a vehicle breaks down.
Philip Goose, community engagement officer at road safety charity Brake, said: “We have serious concerns about the danger of permanent removal of the hard shoulder on motorways.
“The Highways Agency has indicated that they expect only half of the people who break down on these stretches to make it to refuge or off the motorway, potentially leaving them perilously exposed to fast moving traffic.”
The construction work between junctions 23 (A1M) and 25 for Waltham Cross is now complete and work is now underway between junctions 25 and 27 for the M11.