 The tunnel is one of the few single-carriageway stretches of motorway in New Zealand.All that separates opposing flows of traffic is a set of double no-overtaking lines and a series of slim fixed-in-place post-style road bollards.The tunnel was opened as part of the extension of the Wellington Urban Motorway through Thorndon to Te Aro and was originally envisaged to include a parallel three-lane tunnel exclusively for southbound traffic (with the existing tunnel built for northbound traffic only).