Contents: History | Why an Upgrade? | Mangere Bridge Widening | Hillsborough to Walmsey Widening

The Mangere Bridge

The South Western Motorway (SH20) has been under construction to connect to motorways in the north and south since the 1970s. From 1997 to the present the motorway has been extended in both directions from the original section in Mangere & Onehunga. The main purpose of the South Western Motorway is to provide connections to the Auckland Airport. Eventually when connected to existing motorways the South Western will be an alternative to the Southern motorway - completing the currently under construction Western Ring Route Network.

The first section of the South Western Motorway started construction in late 1977, the section was only a short approach to the old Mangere bridge bypassing the busy Onehunga area. The Mangere Bridge after a very long (and disruptive) construction process was completed in March 1983. It connected the already used Onehunga bypass to the newly completed crossing to create a total section between Neilson Street and Coronation Road of 1.8km at four lanes wide (two in each direction).

Under construction in 1982

Recent activity:
- In 1997 the Coronation Road to Puhinui Interchange, and link to Kirkbride Road section was completed.
- The Mt Roskill Extension in May 2009 opened; extending from Hillsborough Road to Maioro Street in the north-west.
- In mid-2010 both the Mangere Bridge duplication & surrounding widening and the Manukau Extension opened. Widening the existing motorway and bridge and connecting the 1997 section to the Southern Motorway respectively.
- One project on the South Western Motorway is still to be completed; the Waterview Connection between the Mt Roskill Extension and the North Western Motorway.

This project is one of the projects of the Western Ring Route. The Western Ring Route will offer a much needed alternative to the congested Northern and Southern Motorways. There are seven projects on this network with five now completed, the Waterview Connection and North Western Widening projects are yet to be completed.

Why did the Mangere Bridge need to be widened?

Congestion: The existing Mangere Bridge no longer met the capacity requirements of the South Western Motorway, with the growth of Auckland Airport and surrounding residential and industrial areas has meant the South Western Motorway is being used to the extent where congestion is created and desirable speeds were not met.

Western Ring Route: Both ends of the South Western Motorway are to be extended to join the Southern and North Western motorways. There will be a significant increase in traffic on the South Western Motorway. This meant the existing Mangere Bridge would become a pinch point.

The Mangere Bridge Duplication

Completed: 31st of August 2010 at $230m.

The Mangere Bridge Widening did not widen the existing bridge but duplicated the existing one to the north east. This means a similar design and height was built alongside the existing Mangere Bridge. Duplication was the most cost effective mainly due to integration with the existing motorway.

The project completed with four lanes in each direction, double the existing capacity. It also includes dedicated bus shoulder lanes in both directions. Provision is provided for extra widening in the future if needed.

Above: Completed spans.

Above: Sequenced image of the Mangere Bridge construction. Click for larger image.

Above: Artists impression of duplicated bridge.	Above: Almost completed structure.	Above: Under Construction.

Hillsborough to Walmsley Widening (outside the bridge lanes)

Under construction | Completion: end of 2011

From Hillsborough Road in the west until Walmsley/Coronation Road further south the South Western Motorway was widened by one to two lanes in each direction (to total between three and four).

Southbound: Widened from two lanes to three between Hillsborough Road and Queenstown Road, from two lanes to four between Queenstown Road (over the Mangere Bridge) to Mahunga Drive and two lanes to three between Mahunga Drive and Walmsley Road.

Northbound: Widened from two lanes to three between Walmsley Road and Rimu Road, from two to four lanes between Rimu Road (over the Mangere Bridge) to Hillsborough Road.

This is the busiest section of the South Western Motorway as most traffic uses this part of the South Western for access to and from the Auckland Airport. This allows existing traffic to tie in with future Western Ring Route traffic.

The motorway was also be improved, to a better standard, addressing issues like the current dips, lane and shoulder widths. Works between Walmsley Road and SH20a were completed in June 2011 to address lane weaving issues.

Above: Widening between Queenstown Road and Neilson Street interchange complete. Before and after.

Above: Widening between Queenstown Road and Neilson Street interchange complete.

Above: Widening progress between Rimu Road and Coronation Road is complete. Looking south.

Above: Widening complete. Taken looking west from Walmsley, with the Coronation Road off-ramp to the left.

Above: Widening progress between Walmsley and the SH20a link (October 2010).