By JASON COLLIE transport reporter

A low-level bridge for local traffic and rail is one of the options being investigated to take the strain off Mangere Bridge.

Transit New Zealand has launched a study into another crossing for the Manukau Harbour because the existing bridge, which carries the Southwestern Motorway, is clogged in rush-hours.

Options include widening the bridge, a new bridge similar to the present one or a low-level crossing for traffic travelling between Mangere and Onehunga. Running rail on a new bridge will also be investigated.

Transport planners estimate almost half of the 80,000 vehicles which travel daily over Mangere Bridge are local journeys between the suburbs either side of the harbour.

The local option would find the greatest favour with Mangere and Onehunga residents, says Mangere Community Board chairman John Wright.

"They have to do something because the bridge is carrying more than it was designed for.

"Both Onehunga and Mangere want a low-level crossing."

Another crossing would also keep access to Auckland Airport open if a major accident closed the present bridge, he said.

Transit project manager John Hughes said the study was an initial look at which options to take forward and investigate.

It would also consider where a new crossing could potentially run, possibly over the same area where the former Mangere Bridge is or east of the present structure.

"In developing options, we will be asking hapu, local communities on both sides of Manukau Harbour and road users for their views," he said.

"It's been on our agenda for quite a while now, because Mangere Bridge is reaching capacity in peak periods and part of our overall strategic vision is to develop State Highway 20 as an alternative to the Southern Motorway."