Weekend Herald

A bridge too far?

‘Strengthen­ing’ woes the latest in the long line of harbour crossing issues

- Tom Dillane

The revelation that the Auckland Harbour Bridge could no longer be “strengthen­ed” is perhaps the final chapter in the cursed history of the city’s infrastruc­ture centrepiec­e.

The NZ Transport Agency says the weight of more steel to make the bridge stronger would compromise its “structural integrity”.

Almost since it opened in 1959 — connecting the CBD to the North Shore — the original box truss fourlane structure was inadequate for Auckland’s fast growing commuter numbers. By 1969 two “clip on” lanes had been added to either side.

Over the next 50-odd years New Zealand’s population grew from 2.8 million to 5 million — a third of that in Auckland.

But the eight lanes on the Auckland Harbour Bridge have stayed the same. The latest reminder of the fragility of the ageing bridge came with yesterday’s announceme­nt that major maintenanc­e on the bridge was no longer possible.

A November briefing paper to Transport Minister Michael Wood warned the “loading restrictio­ns” would be needed within the next 20 years — but Waka Kotahi NZTA general transport service manager Brett Gliddon hints it may actually be much sooner.

Gliddon said active management of traffic on the bridge would not be needed within the next 12 to 18 months but did not elaborate further on a timeframe.

The revelation­s came at the annual review of NZTA at a parliament­ary select committee this week.

After a question from National MP Christophe­r Luxon, Gliddon said it was no longer possible to strengthen the bridge, which is crossed by 170,000 vehicles on weekdays.

“We believe we’ve strengthen­ed it as much as we possibly can and we can’t add more steel into it. It’s counter-productive.”

He said maintainin­g the “structural integrity of the bridge” could involve restrictin­g heavy vehicles, limiting the lanes they could use, the number of heavy vehicles on the bridge at one time, or the time of day they cross.

Auckland’s Chamber of Commerce chief executive Michael Barnett said it was costing “millions of dollars a day” as traffic is diverted because of strong winds on the bridge or roading needing to be fixed.

But Auckland Mayor Phil Goff told the Weekend Herald that NZTA had told him proper maintenanc­e of the bridge will continue to operate “indefinite­ly as a key strategic asset in the Auckland network”.

“It has long been planned for heavy trucks at some point in the future to be required to use the centre lanes of the bridge rather than the socalled clip-on lanes,” Goff said.

“The bridge will continue to be safe and suitable for general traffic.”

Wood hinted yesterday heavyweigh­t trucks may only be able to cross Auckland’s ageing Harbour Bridge at restricted times of day.

“What you can create is a reduction of the very heavy vehicles which, in the wrong circumstan­ce, could create the heaviest risk of some kind.”

But Wood said the Government remains committed to the SkyPath despite Waka Kotahi saying no further weight should be added to the bridge for structural safety reasons.

The Transport Minister said in a couple of months a decision would be made on whether the design of the SkyPath would get the go-ahead from the Government.

“We have to make sure this design is fit for purpose, that it delivers what we want and that it’s also going to be safe and resilient,” Wood said.

“There is very strong commitment from the Government to make sure Aucklander­s have great walking and cycling access, including providing that access, across the Waitemata¯.”

In February last year, the Government included SkyPath in a $6.8 billion New Zealand Upgrade Programme of transport projects and said constructi­on would start early this year.

Wood said $360 million from the fund had been allocated to the SkyPath.

SkyPath was expected to cost $240m and $120m for a shared pathway extension to Esmonde Rd.

On September 18 a freak 127km/h gust of wind tipped two trucks on their sides, severely damaging a loadbearin­g steel strut in the middle of the bridge and causing traffic chaos.

The middle lanes of the bridge were out of action for weeks while a new strut was constructe­d and the broader Auckland network was brought to its knees as a consequenc­e.

Auckland mayoral candidate John Tamihere proposed turning the existing harbour bridge into a twolevel superstruc­ture — with 10 lanes for cars on the lower level and four rail tracks and walkways and cycleways on the upper level.

Goff savaged the plan at the time — saying it would cost more than $10 billion to build and would “bankrupt the city”.

“A new 10-vehicle-lane harbour crossing, which will carry cars, rail, pedestrian­s and cyclists can be completed within six years on the existing bridge piers, replacing the existing bridge,” Tamihere said.

“There will be minimal disruption to traffic. My team have looked at overseas structures and costs and it is very doable.”

The now Ma¯ori Party chief of staff, claimed full or partial superstruc­ture replacemen­ts have been carried out on a number of bridges in the United States, including the Milton-Madison bridge, costing US$104 million ($161m), over the Ohio River. It was built in 1929.

The last major harbour bridge restrength­ening was in 2007 when engineers warned a potential for “catastroph­ic failure” in a worst-case scenario, 920 tonnes of extra steel was bolted and welded on to the clipons to extend the life of Auckland Harbour Bridge.

At the time, restrictio­ns were placed on heavy vehicles using the clip-ons to reduce vibration and help keep the bridge stable during welding of steel inside the box girders.

Today, the clip-on lanes are open to 50-tonne maximum permitted heavy vehicles and heavier vehicles can only use the truss bridge.

Ever since the Auckland Harbour Bridge opened in 1959, a second crossing has been mooted.

And in September last year that prospect was again pushed out to some hazy future date.

Goff said based on advice from Waka Kotahi and Auckland Transport that a new crossing will be needed after 2030.

Over the past 60 years, second harbour crossing schemes have included a new bridge, tunnels under the Waitemata¯ Harbour, a rail crossing and a radical idea of demolishin­g the existing bridge for a new arching structure supporting a splay of cables in the shape of a sail.

The latest NZTA business case for a second crossing came in November last year, and determined a new $5 billion cross-harbour rail tunnel should be built within the next 20 years before any additional roading network.

The report projected that within 15 to 20 years a harbour rail tunnel from the city centre to Takapuna and Smales Farm would be required.

A further $3 billion would be needed to extend the track from Smales Farm to Albany.

Transport experts did not believe a new road connection to ease congestion on the ageing Harbour Bridge would be needed until mid to late 2040 — 10 years after the rail tunnel.

The roading options would then be either expanding the capacity of the existing bridge or $10 billion for a road tunnel from the city centre to Esmonde Rd and additional motorway lanes to Constellat­ion Drive.

 ?? Photo / Nick Reed ?? Transport Minister Michael Wood has been warned “loading restrictio­ns” would be needed on the Auckland Harbour Bridge within the next 20 years.
Photo / Nick Reed Transport Minister Michael Wood has been warned “loading restrictio­ns” would be needed on the Auckland Harbour Bridge within the next 20 years.
 ??  ?? Michael Barnett
Michael Barnett
 ??  ?? Phil Goff
Phil Goff

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