Terrace Motorway Tunnel
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The Terrace Tunnel takes the Wellington Urban Motorway (SH1) under The Terrace in central Wellington, New Zealand. Built in the mid 1970s, it is 460 metres in length.
[edit] Design
The tunnel has three traffic lanes, one southbound and two northbound. This single southbound lane causes frequent congestion during morning rush hour, traffic having to wait for traffic lights just south of the tunnel.
The tunnel is one of the few single-carriageway stretches of motorway in New Zealand. The only thing separating traffic from oncoming traffic is a set of double no-overtaking lines.
A second three-lane tunnel slightly to the east was going to be built for southbound traffic, with the current tunnel becoming northbound only, but this proposal was shelved in the early 1970s as the rising cost of building the single tunnel ruled out duplication for the foreseeable future. Appraisal of expected traffic flows also indicated that the second tunnel would not be needed for many years. A reversible lane (tidal flow) system as used on the Auckland Harbour Bridge was proposed - investigation as part of the tunnel link project found it to be unsafe, but it has not been abandoned. Some of the pillars for the second tunnel are visible in the Clifton Terrace carpark adjacent to the cable car line.
As you enter the tunnel it is impossible to see the other end, as it curves in the middle.
[edit] State Highway Status
When it opened in 1978, the tunnel was the southern end of State Highway 2. Alterations at the Ngauranga SH1/SH2 interchange in 1984 connected SH1 to the motorway (although SH1 continued off the Aotea Quay offramp until 1996), and in the 1996 Transit extended the SH1 status to the entire route from the end of the Wellington Urban Motorway to Wellington International Airport.
