Bridges rise over Mt Roskill motorway

Part of the new foot and cycle bridge to pass over the Southwestern Motorway at Mt Roskill. Picture / Dean Purcell

Two swept-up bridges are fast taking shape over the route of Auckland's motorway link through Mt Roskill as a giant brown slug of bulldozed earth lies sprawled between them.

Although the permitted earthworks season ended on May 1 for winter, civil engineering operations are intensifying on the $169 million project, especially with the laying of initial spans for the bridges above May Rd and Keith Hay Park.

Sixteen of 24 concrete beams needed for the middle of the 254m traffic bridge to take May Rd over the future motorway have been lifted into place at the foot of Mt Roskill's volcanic peak, ready for vehicles to use from October, when a temporary detour will be dismantled.

So has the first of three spans of a 4.2m-wide foot and cycle bridge designed to carry about 2000 people a day between Keith Hay Park and Mt Roskill Grammar School from the end of next month.

Bridge parts have been pre-fabricated nearby, making for rapid assembly of what Fulton Hogan project manager Tony Dickens likens to a three-dimensional jigsaw.

The first span crosses Somerset Rd, which runs along the school's western border parallel to the motorway, and the completed 150m bridge with sweeping approach ramps will be supported by cables running off a 25m-high central pylon tower akin to a giant maypole.

Its reach also covers a designated corridor for a possible railway line between Southdown and Avondale.

Grammar deputy principal David Lett expects the bridge will be an impressive spectacle and is relieved Transit NZ agreed to extend it over Somerset Rd, which is crossed daily by hundreds of students from a cluster of three schools.

The bridge is 5.5m above the road, but he said he was confident its 1.4m handrails would be high enough to stop pedestrians and cyclist falling or being pushed off.

Mr Dickens' team will eventually build six bridges over the motorway route, four for vehicle traffic and two just for pedestrians and cyclists.

Work on a temporary bypass of Dominion Rd will start in July, before a traffic bridge is built there as part of a full interchange for the 4km motorway, which is due to open in early 2009 as far as Maiora St in New Windsor.

Completion of the May Rd bridge by spring is needed for about 100,000 cubic metres of earth stockpiled from excavations around Hillsborough Rd and elsewhere to be moved to the western end of the motorway route for the carriageway foundation.

The bridge is about 4m above ground level, and the motorway will be dug 4m below that.

A large mobile crushing machine has meanwhile begun a trial of grinding the first batch of 114,000cu m of volcanic ballast rock from the northern toes of the Roskill mountain.