Auckland Harbour Bridge

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Auckland Harbour Bridge
The bridge from Watchman Island, west of it.
Carries	Motor vehicles
Crosses	Waitemata Harbour
Locale	Auckland City/North Shore City, New Zealand
Maintained by	Transit New Zealand
Designer	Freeman & Fox
Design	Box truss
Material	Steel
Longest span	243.8 metres
Total length	1,020 metres (3,348 ft)
Clearance below	43.27 metres at high tide
AADT	168,754
Opening date	30 May 1959
Toll	Until 1984

The Auckland Harbour Bridge is an eight-lane, box truss motorway bridge over the Waitemata Harbour, joining Saint Marys Bay in Auckland City with Northcote in North Shore City, New Zealand. The bridge is part of State Highway 1 and the Auckland Northern Motorway. It is also the second longest road bridge in New Zealand, and the longest road bridge in the North Island.^[1]

The bridge has a total length of 1,020 m (3,348 ft), with a main span of 243.8 m, rising 43.27 m above high water^[2] allowing access to the deepwater port at the Chelsea Sugar Refinery west of it (nowadays one of the few wharves needing such access west of the bridge).

1 Background
2 Construction
3 Traffic management
4 Second Harbour Crossing
5 See also
6 References
7 External links

[edit] Background

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Prior to construction of the bridge, the quickest way of getting from Auckland to the North Shore was via one of the regular passenger or vehicular ferries. By road, the shortest route was through West Auckland via Riverhead and Albany, a distance of over 40 kilometres.

[edit] Construction

[edit] Initial structure

The bridge took four years to build and was opened on May 30, 1959 by Prime Minister Sidney Holland, with four lanes of traffic, two in each direction. Four men were killed during construction, and their names are recorded on a memorial plaque underneath the bridge at the Northcote end.

The bridge started out as a toll bridge, with toll booths for both north and south-bound traffic located at the northern end. Tolls were originally 2/6 (25 cents) per car but were reduced to 2/- (20 cents) after 15 months of operation. Later, tolling was made south-bound only before being finally discontinued on March 30, 1984, and the booths were removed.^[3] This was in line with political commitments that tolls would only be charged until the bridge's construction costs were paid off.

[edit] 'Nippon clip-ons'

Support structure under the bridge.

The bridge was originally built with four lanes for traffic. Owing to the rapid expansion of suburbs on the North Shore and increasing traffic levels it was necessary to increase the capacity of the bridge.

In 1969 two-lane box girder clip-on sections were added to each side, doubling the number of lanes from four to eight. The sections were manufactured by Japanese contractors (Ishikawajima-Harima Heavy Industries), which led to the nickname 'Nippon clip-ons'. The selection of the company was considered a bold move at the time, barely 20 years after WWII and with some considerable anti-Japanese sentinemt still existing in the country.^[4]

In 2006, it became public that cracks and signs of material fatigue had been found in the clip-on lanes, which have an expected lifetime of 50 years.^{[citation needed]} Auckland City Council Transport Committee requested Transit New Zealand to investigate the future of the clip-on lanes as part of its 10-year plan. Transit noted in this context that the plan already includes some funding for bridge maintenance.^[5]

In May 2007, Transit New Zealand proposed a bylaw change to restrict trucks over 4.5 tonnes from using the outside lane on each clip-on. This is to reduce stress on the aging structure.^[6] This was later changed to a less strict bylaw introduced in July 2007 restricting only vehicles of 13 tonnes or more, based on the high level of voluntary compliance during the previous months.^[7]

In 2007, it was announced that NZ$ 45 million in maintenance work on the clip-on sections was being pulled ahead as part of good practice. However, in October 2007, a 2006 report from Beca Group surfaced in the press, noting that the clip-ons were at risk of catastrophic, immediate failure in certain circumstances (such as a traffic jam trapping a large number of trucks on them). Transit New Zealand has noted that the situation described was extremely unlikely, and measures already implemented would prevent it from occurring.^[8]

[edit] Proposed extension

The bridge in its current form can only be used by motor vehicles (tourists can walk on the span via guided tours). In recent (2007) discussions about the future of the bridge, the addition of a cycle and footpath link between Auckland City and North Shore City has been mooted for the bridge. Transit New Zealand has noted that such a provision would cost between 20 and 40 million NZ$, but public support for such an addition to the bridge has been polled as being very high.^[9] Cycle Action Auckland meanwhile notes that lower-cost options are available, and that a cycleway could relatively easily be included in the bridge strengthening works currently being planned for the clip-on structure.

Cycle Action Auckland has created a webpage showcasing the proposed walking / cycling solution and invites visitors to sign a petition supporting or opposing the proposal.^[10]

[edit] Traffic management

A "tidal flow" system is in place where the traffic direction of two of the centre lanes is changed in order to provide an additional lane for peak period traffic. During the morning rush, five of the eight lanes are allocated to southbound traffic heading towards Auckland. This situation is reversed in the afternoon, when five lanes are allocated to northbound traffic. At all other times of the day the lanes are split evenly, and peaks also have grown increasingly evenly distributed (i.e. whereas in previous decades (as late as 1991), there was often a higher than 3:1 difference in directional traffic, this has now (2006) dropped to around 1.6:1). The bridge has an estimated vehicle capacity of 180,000 per day, and in 2006 had an average volume of 168,754 vehicles per day (up from 122,000 in 1991).^[11]

For many years lane directions were indicated by overhead signals. In the late 1980s a number of fatal head-on accidents occurred when vehicles crossed lane markings into the path of oncoming traffic. In the 1990s, a movable concrete safety barrier was put in place to separate traffic heading in opposite directions and eliminate head-on accidents. A specially designed barrier machine moves the barrier by one lane four times a day,^[12] at a speed of 6 km/h. It takes 40 minutes to move the entire barrier.

[edit] Second Harbour Crossing

Bridge from the Sky Tower, southeast of it.

Main article: Second Harbour Crossing

Almost since the Harbour Bridge reached capacity (i.e. before extension via the clip-ons) a second crossing of the harbour was mooted. The extreme costs and the difficulties of connecting it to the motorway network have however so far caused plans to remain at concept stage. However, in 2008, a study group narrowed down arund 160 options to a single recommendation, a multi-tunnel link approximately one km east of the existing bridge, with up to four individual tunnels for motorway and rail traffic. The proposal however has no funding assigned to it yet.

[edit] See also

General

Specific

Central Motorway Junction, the major motorway junction connecting southeast of the bridge
Newmarket Viaduct, similarly important traffic bottleneck on other side of Auckland CBD
Western Reclamation, large industrial area east of the bridge, possible site of 2nd crossing