Here’s everything you need to know….
Why are they closing the road?
Kent County Council chiefs say the existing lighting system in the Chestfield Tunnel needs to be replaced as it uses fluorescent lamps approaching the end of their life, as they will no longer be available after August.
The authority is planning to replace the lights and the support system with LED technology.
This will make it more energy efficient and will help to reduce carbon emissions.
What closures are planned?
The first took place last night, with the New Thanet Way shut in both directions between Herne Bay and Whitstable.
The same stretch will be closed again from 8pm to 6am tonight and tomorrow night before a contraflow system is introduced.
Further down the line, there will be more complete closures overnight between May 26 and May 30, and on June 30.
What is a contraflow and how will it work?
A contraflow is a traffic management system, similar to that used on the M20 during Operation Brock.
It will be put in place over two phases in a bid to keep traffic moving while the work is carried out.
It means one side of the dual-carriageway will be split into two single lanes so traffic can flow in opposite directions on the same side.
The first phase will be on the coast-bound carriageway.
It will start from 8pm tomorrow (Sunday) and be in place until Friday, May 26.
Phase two will see it move to the London-bound carriageway.
This will start from 1am on Tuesday, May 30, and last until 5am on Friday, June 30.
There will be a temporary, mandatory 40mph speed restriction on the A299 Thanet Way in both directions between the Golden Hill overbridge and the Thornden Wood Road overbridge, and where indicated by signs.
What will the impact be?
Huge queues are expected on the Thanet Way as lower speed limits are brought in to facilitate drivers crossing the carriageway to join the contraflow system.
Kent County Council initially wanted to reconstruct the carriageway at the same time - which would have seen the road shut in alternate directions between the end of April and the end of June.
But in the wake of warnings the closures would have caused traffic chaos, the project was shelved.
When will they carry out the carriageway reconstruction now?
At a later date yet to be decided.
When it does happen, it is likely to cause more misery for drivers as the work involved could mean complete closures are needed.
Is there a way to avoid it?
Many motorists will choose to come off the New Thanet Way and join the Old Thanet Way, taking them through Whitstable and Herne Bay before rejoining the dual-carriageway.
What impact will this have on businesses in Herne Bay and Whitstable?
It is expected to cause lots of traffic in Whitstable and Herne Bay, which already get snarled up during busy weekends when the sun comes out.
Business owners in the towns believe the hold-ups will cause traders to lose a sizeable chunk of their custom at the start of the summer.
Was the plan always to use a contraflow system?
No. The highways department changed its mind, particularly after some crashes closed the New Thanet Way and had a knock-on effect on traffic on the Old Thanet Way.
How long will it last?
The project is expected to last 10 weeks, from Sunday until 5am on Friday, June 30.
Engineers will begin putting the barriers up tonight ahead of the main work starting tomorrow.