Workmen are operating around the clock to carry out vital repairs at Spaghetti Junction and have reached the half-way stage of the project, despite heavy, persistent rain.
Highway England issued the update to thousands of frustrated, diverted drivers who are regularly caught up in queues on surrounding roads.
A Highways England spokesman said: “Since the scheme started more than 158 locations where concrete was damaged have been repaired and replaced – that’s the equivalent of more than four ambulances full of concrete or 74 shopping trolleys in volume.
“Work is taking place around the clock to carry out vital concrete and waterproofing repairs to the ageing 45-year-old structure that carries more than 200,000 vehicles a day.
“Last weekend saw the scheme reach the half-way mark with work progressing well despite more torrential downpours and severe weather across parts of Birmingham.
“The dedicated teams are continuing to work 12hr shifts in a bid to complete the programme as quickly as possible.”
The M6 has remained fully open during the work.
But for the duration of the scheme there is no access to the A38(M) from Gravelly Hill or Tyburn Road, with local diversions in place.
And at the weekend the A38M has been fully closed, leading to some particularly long delays for motorists.
But Highways England insisted it was necessary and would mean the difference between the working being completed in seven weeks rather than 30 weeks.
Project manager Jessica Kenny said: “While we understand that nobody likes roadworks, the full weekend closures have allowed repair crews greater access to the carriageway compared to working in smaller sections when the road is kept open.
“This means we can work quicker and more safely to complete the scheme as quickly as possible.
“And by doing this work in this way, it means that our crews have shortened the duration of the scheme considerably.”
Key link roads will remain closed until September 4 with other local routes set to remain busier than usual.
Drivers are advised to plan their journey and allow extra time.
For more information, go to http://roads.highways.gov.uk/regions/west-midlands