Work has begun to remove or encapsulate asbestos in the historic Grade II-listed Tyne Pedestrian and Cyclist Tunnels under the river between Howdon and Jarrow.
It is expected to take specialist contractors until Christmas to complete the works.
However, the tunnels are being handed back to their owner, the North East Combined Authority (NECA), in stages to enable refurbishment works to re-commence as early as possible.
The tunnels were closed for refurbishment in May 2013. A series of setbacks, including the discovery of the extent of asbestos contamination, as well as corrosion, coupled with the collapse of the original contractor GB Building Solutions, has delayed the project.
The tunnels are now expected to re-open in Spring 2018.
A free-to-use replacement shuttle bus service for up to 24 passengers and 16 bicycles and a Night Service for shift workers will continue to operate.
Alastair Swan, principal engineer for the tunnels, said: “This is a positive step forward in restoring the tunnels as a vital piece of cross-Tyne infrastructure for cyclists and pedestrians.
“Despite the difficulties we have encountered, we remain committed to the refurbishment of the tunnels.”