A dreaded contraflow system is set to return on the A299 Thanet Way tonight for at least three months while emergency safety works take place.

The dual-carriageway has been completely shut off between Herne Bay and Whitstable since a dangerous fault was identified with jet fans in the Chestfield Tunnel during a routine inspection on Tuesday.

An emergency closure was introduced on Tuesday 11 June so that specialist engineers could get on site to bring the London-bound lane back up to a safe operational level so at least part of the tunnel can open.

The jet fans on the coast-bound side will need to be replaced.

The contraflow will run for approximately 900 metres long and will allow one lane to remain open in both directions, where the speed limit will reduce to 40mph.

It will be in place for at least three months, news which is sure to exasperate motorists.

The jet fans used to ventilate the tunnel are specialist pieces of kit which are manufactured to order and then delivered and installed on site by a specialist crew.

It is expected that it will take at least two months, dependent on availability, to manufacture and deliver the fans, and the contraflow will need to be in place until the specialist crews can safely install them.

The closure has pushed traffic onto alternative routes, with the A2990 Old Thanet Way bearing the brunt of rush-hour queues.

It comes not even two weeks after a previous contraflow system was removed following a six-week project that saw a stretch of the coastbound side of the A299 reconstructed near Whitstable.

During that time motorists faced delays of up to 45 minutes between Herne Bay and Dargate.

This work is separate to the A299 Thanet Way works completed last month.

Kent County Council says it had no choice but to close the A299 this week given the safety issues uncovered on Tuesday.

A spokesperson said: “The fans are the primary safety and key ventilation system in the tunnel and are critical in the event of a fire. They help fire crews to safely evacuate people and can help to disperse traffic pollution.”

They added the power of the fans will have to be increased to a safe level in the London-bound section of the tunnel before the road can reopen with the contraflow.

Simon Jones, corporate director of growth, environment and transport, said: “We understand this is a huge inconvenience to residents and we apologise for the disruption encountered, however, our priority is public safety, which we take very seriously.

“The contraflow will enable us to keep at least one of the tunnel lanes open so that people can continue to use that stretch of road. However, please allow extra time for journeys as there will unfortunately be some delays.

“When the equipment manufacturer confirms when the fans can be delivered back to the site we will provide a further update on when we will be able to safely remove the contraflow and re-open the tunnel fully.”

Kent Fire and Rescue service area manager, Charlie Smith, said: “These are essential works to repair jet fans in the tunnel, which will support our crews in the safe evacuation of the public in the event of a fire”.