ContractorNZTA project

The Normanby realignment project: fixing a killer bridge in South Taranaki

One of the most important NZTA projects in the South Taranaki District for decades is the State Highway 3 Normanby realignment project, which includes the demolition of the old “killer overbridge” and its replacement, a “road under rail” underpass. NEIL RITCHIE explains.

C_July_2015_Pg36_1THE NORMANBY REALIGNMENT project officially got underway several months ago when Transport Minister Simon Bridges turned the first sod of dirt in the two-year-plus programme that will see the 75-year-old overbridge and its substandard approaches replaced by the “road under rail” underpass and a new stock underpass.

From mid-2017, this will see vehicles travelling underneath, rather than over, the existing New Plymouth to Marton railway line, as well as travelling along a straighter, smoother and shorter stretch of this important part of State Highway 3 (SH3).

And eliminating the old substandard curved bridge and infrastructure should also see a marked reduction in the number of accidents in an area that has had an average of five each year over the past decade, including some fatalities.

A grader works on the sub-grade improvement layer for the construction of the Normanby rail diversion with Mount Taranaki in the background.
A grader works on the sub-grade improvement layer for the construction of the Normanby rail diversion with Mount Taranaki in the background.

A car and van collided on the overbridge during 2005, with the van catching fire, resulting in three fatalities, three serious injuries and a minor injury. And two male motorcyclists in the annual children’s charity ride, Round the Mountain Toy Run, died as a result of another accident on the overbridge during 2012.

With the old bridge’s poor safety record, the Taranaki Regional Council has had the overbridge and its approaches in it sights for at least a decade as a key priority in its Regional Land Transport Programme.

And this project, which has been identified as a problem part of SH3 in Taranaki, is also part of the Government’s 2014 Accelerated Roading Package.

NZTA awarded Downer the main $10.2 million construction contract last December and project manager Iain Fletcher says Downer is utilising “a combination of Downer resources and subcontracted resources and, where at all possible, using locally based subcontractors and suppliers in an effort to support the local community and economy”.

Initial top soil stripping and trucking away.
Initial top soil stripping and trucking away.

Improved signage, road markings, road surfacing and a reduced speed limit (70 kilometres per hour), as well as a diversion around the existing overbridge, have been in place for several months now to improve road safety during the realignment project four kilometres north of Hawera.

Iain says Downer is taking particular care with this four and a half kilometre long project, given that work is happening adjacent to the existing railway line, “which is an historic site having been constructed over 100 years ago.

“There are also records of early European activity, as well as potential Taranaki War skirmishes in the area … these factors have led to an active archaeological interest in earthworks activities.

“And due to the length of this site, and the opportunity to re-allocate resources to other areas if necessary, we are able to continue works without delay if any area requires further investigation.”

Downer is also expecting to encounter ground water in some places – “as there are deep cuttings immediately to the north of the new bridge location for example”.

Base course being spread for the temporary road diversion.
Base course being spread for the temporary road diversion.

“However, the more technically challenging section of the site will be the installation of the new four metre by four metre stock underpass through the rail corridor.

“Trains run on this line from Monday morning through to Friday night and, in order to retain full control over our construction programme, we have opted to work under a ‘line impassable’ stopping operation rather than a full ‘block of line’. The key benefit of this approach is that it gives us greater flexibility in the programming of the works.

“This has also led us to develop a methodology that involves all materials and plant to be sourced and on site ahead of time, enough personnel to allow continuous around the clock shifts and thoroughly reviewing the work plan, including contingencies for all eventualities.”

Downer has to divert the existing railway line at the northern end of the site before construction of the new bridge can begin and this involves constructing a diverted line to the west of the bridge site within a confined area, between local roads, new road construction and the existing live railway. “Strict safety measures are in place for this.”

Materials for the project, consisting mainly of roading aggregates and concrete, are being sourced locally, with Downer’s “highly experienced pavement crews” ensuring top quality roading and pavements.

C_July_2015_Pg36_5“The new road corridor also passes through several existing farms. And farm land must be regarded as part of a business, rather than just part of the countryside – this is where the farmer earns his living, in the same way as commerce is carried out in a city centre.

“To this end, we have endeavoured to keep our impact on the overall footprint of the site to a minimum to ensure that grazing is as uninterrupted as possible and that we provide access to annexed land for grazing whenever we can.

“And care is being taken throughout the duration of the works to ensure that we are not unduly interrupting the farmer’s operations, from dust nuisances through to temporary loss of farm races.”

This section of SH3 is a key freight route for Taranaki, carrying 6000 vehicles or more a day, with 15 percent of those being heavy vehicles. The realigned highway will head north on the western side of the railway line, linking back via the underpass and providing a straighter, smoother and shorter (by about 500 metres) route across this stretch of highway, bringing it up to current design speed standards (of 100 kilometres per hour) and eliminating five substandard curves.

The “road under rail” underpass will also make the highway more resilient to closure and disruption arising from future crashes and natural events such as earthquakes.

Iain adds that initial work is going well.

This includes the temporary rail diversion, facilitating the construction of the new rail bridge on the current rail alignment; the new alignment of Te Roti Road at the northern extent of the project, which includes the new rail level crossing in that area; and bulk earthworks that are now finished for the winter due to weather conditions.

Piling works for the new bridge started during June and are due to be completed about August and preparations are also underway for the construction of the new stock underpass, due to start in July.

NZTA’s highway and network operations project team manager John Jones says: “We appreciate that this project has been a long time coming and we recognise and appreciate the efforts of the local community.”

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