The end is nigh

NZ Transport Agency acting regional manager Tommy Parker welcomed the first motorist onto the Hayr Road Bridge after an official ribbon cutting ceremony in October. The new bridge is the last of six to be built crossing the motorway on the Mt Roskill Extension project in Auckland.

The $186 million, four-kilometre long State Highway 20 Mt Roskill Extension project is scheduled to open in March next year and is part of the central section of the Western Ring Route. The strategic route will eventually provide an alternative to State Highway 1 between Manukau City and Albany. It will play an important role in reducing central Auckland congestion, by enabling traffic to completely bypass the Auckland Harbour Bridge, and provide considerable relief to the local roads are currently carrying large volumes of regional or through traffic.

The contract for construction was signed by Fulton Hogan back in April 2005. Four months later work officially began with a sod turning ceremony.

The next celebration came in December 2006 as the first major structure on the project, the May Road Bridge, was opened. Constructed in 12 months at a cost of $6 million, the 61 metre structure comprises 24 individual deck beams and is held up by two very slender piers, each only 300mm thick. Around 15,000 vehicles per day are expected to use the bridge when the motorway is completed.

The May Road Bridge opening was soon followed by two more – the Keith Hay Park Bridge was opened in February 2007 and the Ernie Pinches Bridge the following month. The two pedestrian bridges were the first examples of cable-stayed bridges in the country (see Contractor, August 2008), and cost $1.2 million each.

Both bridges are 170 metres long, contain 13 pre-cast concrete decking slabs and with piers that are 600mm square at the base spreading to a ‘Y’ shape at the top. Located near a number of primary and intermediate schools, the Keith Hay Bridge is expected to have 2000 people per day use it, while another 500 will use the Ernie Pinches bridge.

In October 2007, the NZTA opened the first section of the new, four-lane Dominion Road Bridge. Fully completed a month later, the bridge provides extra capacity for those travelling directly to the city from Hillsborough and Lynfield. It also helps to ease congestion on Dominion Road – one of Auckland’s busiest routes. Supported by a 31 metre long pier, the bridge is 40 metres long and made up of 26 individual deck beams and is expected to carry nearly 13,000 vehicles per day when the motorway is completed.

The next milestone in the project was the opening of the Hillsborough Road overbridge in December 2007. The difficulty with the bridge construction was the fact that the roads were being used by high and unbalanced traffic flows in the morning and afternoon peaks and had to be accommodated during the construction staging without disruption.

Fulton Hogan proposed an innovative concept whereby the motorway overbridge construction would take place in the central island of a large diameter roundabout.

Signalisation of the roundabout was considered necessary because of the sheer volume of traffic during peak times – so the 120 metre diameter roundabout was unique in that four sections of traffic signals were installed within it, meaning motorists sometimes had to stop within the roundabout.

The roundabout opened in January 2007 and was expected to be in place until 2009 – to give enough time for the contractors to build the new overbridge for the interchange, lower the motorway in the centre of the roundabout and construct the off-ramps for the bridge, all while live traffic operated on the roundabout above – however the bridge was completed in excellent time and the roundabout decommissioned a year earlier than expected.

Construction of the $1.5 million overbridge took 11 months and was the fifth of six bridge crossings to be built. Supported by an eight metre pier, the bridge is 40 metres long and made up of 26 individual deck beams. The bridge is expected to carry nearly 40,000 vehicles a day when the motorway is completed.

Last month’s opening of the Hayr Road Bridge, the sixth and final bridge in the project, signals the coming completion of the project.

The $5.9 million bridge is 160 metres long and 5.5 metres high and is made up of seven spans, each comprised of six concrete beams. It too will carry local traffic over the new State Highway 20 motorway.

All bridges have been designed to allow for dedicated bus shoulder lanes and the future provision for a rail corridor to pass beneath them on the northern side of the motorway.

The project also includes construction of a new Auckland City Council cycleway.