The upgrades will improve the safety and quality of customer journeys between Wood Lane to Marylebone Flyover, which is used by 96,000 vehicles per day.
Costain will replace six cantilever expansion joints on the Westway viaduct and carry out resurfacing and concrete repairs on a 2km section of road over the next two years.
The detailed design should be complete by late 2023, with construction starting on site in 2024.
Andy Clarke, Director for Integrated Transport at Costain, said: “Our talented team, which includes Chevron and Freyssinet, set the bar for best practice delivery during the first phase of the project.
“Not only did the A40 remain open to the public throughout the works, but the project was completed five weeks early and under budget. This is the yardstick against which we’ll measure our success on this project.”
Mike Hardaker, TfL’s Director of Capital Delivery, said: “We’re determined to ensure Londoners can move around the capital safely and easily, which is why we’re carrying out vital maintenance works on the A40 Westway.
“The A40 is one of the busiest roads on our network and this next phase of work will allow us to replace joints along the road, ensuring the road can continue to run safely and reliably for years to come. We’ll continue to work closely with Costain to minimise disruption to people using the road and living in the area while this vital work takes place.”