The second phase of a £3m project to improve the M5 near Bristol is set to start on Monday.
The northbound on-slip road at junction 19 will be widened from a single to a dual lane merge slip road and work is expected to take 17 weeks.
It is hoped the works will reduce queuing on both the Portbury Hundred and Martcombe Road approaches.
Barrier work and resurfacing will mean some overnight slip road closures and a different route will be signposted.
The works are being carried out jointly between the Highways Agency and North Somerset Council.
Creation of a high occupancy vehicle/bus lane on the Martcombe Road approach as part of the Greater Bristol Bus Network (GBBN) is dependent on the work.
Phase one of the works were completed just before Christmas.
This included refurbishing traffic lights, replacing crash barriers, drainage repair works, and the strengthening and resurfacing of the gyratory section of the roundabout.
The council's deputy leader, Councillor Elfan Ap Rees, said: "Savings are being made for both us and the Highways Agency by doing these roadworks jointly, and the overall period of time to carry out the roadworks on site is being significantly reduced.
"Traffic flows have already improved as a result from phase one work and by the time all the improvements are in place the misery of prolonged hold-ups for motorists in this area should be a thing of the past."