There has been a long-standing designation for a second parallel tunnel to the north, in order to relieve peak period congestion resulting from lane merges at both ends of the tunnel. A pilot tunnel was bored through in 1974 to investigate the technical feasibility and still exists, although the eastern end has been bricked up and the western end lies on private property. Plans to build the second tunnel paralleled the original plan to complete the Wellington Urban Motorway to the tunnel to provide a motorway bypass of the whole of central Wellington. The second tunnel component was shelved indefinitely in 1981 when budget cuts meant that a scaled-down motorway extension was proposed that would terminate at the existing tunnel.