A video report from our Merseyside Correspondent Andy Bonner:
It was a remarkable feat of engineering - built by the courage of workers 50 years ago.
The Kingsway Tunnel took five years to build and was officially opened by the Queen on the 24th of June in 1971.
Locals still call it the 'New Tunnel' to Wallasey compared with the 'Old Tunnel' which goes to Birkenhead and was opened in the 1930s.
The Kingsway Tunnel is a mile and a half long and around 16 million vehicles pass through it every single year.
Initially it was only one tube with two lanes, it was built with the help of the 35-tonne Mersey Mole - a 45ft long tunnelling machine previously used to build the Mangla Dam in Pakistan.
The new crossing under the Mersey in 1971 attracted huge crowds when the Queen carried out the official opening.
It took a further three years to complete the tunnel's second, more northerly tube which opened to traffic on February 13, 1974 - finally giving Kingsway the four lanes which are used today.
Its architect Tom Harker remembers workmen having to dig close to the riverbed when the tunneling machine broke down.
Video of Tom Harker, tunnel architect