Construction has begun of a bridge to allow pedestrians and cyclists to get between Mangere Bridge and Onehunga without having to contend with road traffic.

Contractors involved with the $230 million Manukau Harbour motorway crossing duplication project are preparing to sink foundations for the bridge to span Onehunga Harbour Rd, which carries traffic to and from the Southwestern Motorway.

The 3.5m-wide concrete structure will extend the reach of the old Mangere Bridge, which was built in 1914 and is still used.

It will allow users to get to and from Onehunga Mall without crossing a road which carries fast-moving traffic around a sweeping bend with restricted sight lines.

The construction alliance building a duplicate Mangere motorway bridge for the Transport Agency expects to complete the footbridge by the end of August.

An underpass beneath the northern abutment of the twin motorway bridges, which is shunned by many local residents for security reasons, will also be upgraded. Lights are to be installed, its floor is to be raised, and a mural painted along its northern wall.

Onehunga Enhancement Society chairman Jim Jackson yesterday welcomed the new footbridge and underpass plans, but believed it would still remain too threatening for some people to use at night, and alternative paths were needed.

The Transport Agency contractors also intend building a footpath on the northern side of Onehunga Harbour Rd as an alternative route.

But Mr Jackson's group wants a footpath on the other side of the road as well, which would include a connection with the Waikaraka cycle and walkway along the Onehunga foreshore to Southdown.

The contractors are also upgrading a cycleway along Onehunga Bay to Queenstown Rd, and are less than a month away from opening a new walking and cycling bridge between Seacliffe Rd and Beachcroft Ave, to replace an existing structure which is not long enough to span the newly widened motorway leading to the harbour crossing.