The traffic at the Birkenhead tunnels was getting heavier and was causing congestion throughout Birkenhead, this was compounded by the traffic lights inside the tunnel for the Birkenhead dock branch. The whole thing needed replanning which included creating the various flyovers.
The north bound Chester Street traffic had to cut across the A41 Southbound traffic from the tunnels and so a tunnel was built under the A41 rather than a set of traffic light backing the southbound traffic into the tunnel area.
The northbound Chester Street traffic was to try and avoid putting the docks and Wallasey traffic through the centre of town.
At the same time all the toll booths were moved to the Birkenhead side, because the land was cheaper.
Plans were approved in 1966 and the whole scheme was completed by July 1969.