West Coast road-rail bridge opens early


The new $25 million Arahura road-rail Bridge on the West Coast officially opens this Friday 11 December 2009 - several months earlier than planned.

The new $25 million Arahura road-rail Bridge on the West Coast officially opens this Friday 11 December 2009 – several months earlier than planned.

One of the largest bridge projects on the New Zealand rail network in recent times, the new structure replaces a wooden, single-lane road-rail bridge which for more than 120 years provided a crucial link over the Arahura River for both State Highway 6 and the Hokitika Branch Railway line.

KiwiRail Chief Executive Jim Quinn said the early completion was a testament to those involved as replacing the historic bridge had been complex.

“This hasn’t been a typical rail bridge project – instead we’ve created a single-track railway, a two-lane road and a pedestrian / cycle way all on the same foundations,” Jim Quinn said. 

“The old bridge was nearing the end of its life so securing this vital transport link for the future was important for the West Coast. This supports KiwiRail’s ongoing programme to remove timber from its rail bridges. It is all about improving the reliability and efficiency of the network to meet the demands of rail’s customers.”

NZ Transport Agency Regional Director Mark Yaxley said around 3,500 vehicles use the bridge each day which meant one of the main requirements of this project was to keep State Highway 6 operational while the new bridge was built.

“As well as keeping the road open while the bridge was built around it, construction was also staged to manage both the whitebait and dairy dry seasons,” Mark Yaxley said. 

Mr Yaxley added that having the bridge open ahead of plan is a sign of how successfully the different demands have been managed.

“Both NZTA and KiwiRail feel that the help and co-operation of the local community, including owners of the riverbed, Mawhera Incorporation has been central to the success of this project.”

Physical work on the new bridge began in mid 2008 with the installation of foundations on either side of the original structure. Traffic was diverted onto one road lane of the new bridge early in 2009 before work began during the dairy dry season when trains do not use the line, to decommission the old bridge and replace the rail line.

New guide banks were formed as part of the bridge project to reduce flood risks.  Further safety improvements were achieved by raising the bridge to allow bigger floods underneath.

A single span from the original bridge has been retained to be used in a small heritage park nearby, which will be completed and opened early in 2010.

Issued by KiwiRail and NZTA

Media contact:

Ruth Larsen, KiwiRail, 04 493 3383, 021 804 906
Bob Nettleton, NZTA, 03 951 3005, 021 954 928

New Arahura Bridge Key Facts

  • Cost $25 million.
  • The bridge carries about 3,500 vehicles and up to four trains a day.
  • It is 220-metres-long.
  • 3700 cubic metres of ready-mixed concrete, weighing 9000 tonnes, was used in construction.
  • The bridge contains 750 tonnes of reinforcing steel and 16 kilometres of post-tensioning strand, weighing 125 tonnes.
  • 540 tonnes of structural steel was used in the rail bridge.
  • 600 metres of new rail formation, ballast and sleepers were required.
  • A total of 840 metres of rail was required for the length of the rail works and 730 new timber sleepers fitted on the rail bridge.
  • Each pile is 25 metres long and driven 20 metres into the riverbed. The piers are 20 metres long and the spans 24 metres.

Building the new bridge

  • Work on the new bridge started in mid 2008. The new single lane road deck was opened to traffic on 25 May 2009. The last train over the old bridge travelled on 7 June 2009 and the first train over the new bridge on 4 September 2009. Finishing touches to the second road lane were completed in December 2009.
  • Keeping State Highway 6 operational was a priority. Apart from brief periods when it was closed so temporary bridge structures could be put in place, the road remained open.
  • Access was maintained for up to four daily Westland Milk Products’ trains until the June-August 2009 dairy dry season.
  • Work was staged to ensure there was no construction activity in the river during the whitebait season.
  • One of the most demanding parts of the project involved hammering the piles 20 deep into the riverbed. Part of the waterway and bridge design brief was to lessen the number of piles to minimise flooding and scour issues.

Some innovation

  • For the first time in the southern hemisphere, a rubber panel system was used in the roundabout level crossings. This provides a rubber section which compresses and rebounds as trains travel over the crossing but at other times provides a flat crossing for motorists and cyclists.
  • The new bridge will reduce the risk of flooding – it is between 0.6 and 1.2 metres higher, to allow larger floods to flow underneath. Significant river guide banks were constructed from gravel recovered from the Arahura River supported by rock from a nearby quarry. These funnel floodwater under the bridge and protect the abutments and the Arahura Village downstream.
  • Rail was used to transport heavy construction materials to the site. All of the 99 road beams were made in a pre-cast factory in Rangiora then railed to the bridge site where they were lifted by crane directly onto the new piers. Steel elements of the rail bridge were manufactured in Napier before being railed to the site where they were assembled and installed.

Preserving history

  • The previous Arahura Bridge was listed as a heritage structure by the NZ Historic Places Trust.
  • To acknowledge its heritage status, one of its original Howe Truss spans has been retained.
  • This span will be the feature of a small heritage park, to be built at the southern approach to the new bridge.
  • Other parts of the old bridge have been used elsewhere on the rail network.