Almost $3 million will be spent designing a long-awaited replacement for the one-lane Kopu Bridge, notorious for holding up motorists heading for the Coromandel Peninsula.

State funding agency Land Transport New Zealand yesterday announced it was spending $2.9 million to design a 480m-long bridge, 13m wide, with two general lanes and a dedicated pedestrian and cycle way.

The design work will be spread over two years and it remains unclear when construction will begin on a project likely to cost at least $31 million.

But it will take only about 18 months to build and the Waikato regional land transport committee hopes an allocation of Government money for regionally important projects through a new petrol tax next year will allow the bridge to be completed by the end of 2007.

That would be four years earlier than outlined in Transit New Zealand's 10-year state highway plan.

The existing bridge, which opened 76 years ago with a central swinging span to allow large vessels to pass up and down the Waihou River, can at peak holiday times delay motorists for up to 90 minutes in queues stretching more than 14km along State Highway 25.

Local residents face delays even on normal week days, when an average of about 8300 vehicles cross the bridge.

Annual traffic growth on the bridge has been about 10 per cent for each of the past two years.

Land Transport chairwoman Dr Jan Wright said an estimated $92 million in travel time savings would be made over 25 years in allowing the project to proceed.

Transit project manager Barry Dowsett said the new bridge would be constructed no more than 20m upstream of the existing structure, which would be developed as a historical attraction with a Category 1 listing on the Historic Places Trust register.

The new structure was likely to be built in 25 spans, to minimise riverbed scouring by matching the configuration of the old bridge, although there was a possibility the number of sections could be halved.

Mr Dowsett said it would be 6.5m above the river at mean high water, compared with the 3.5m height of the existing bridge.

Hauraki District Mayor John Tregidga said the design funding was not before its time and he would keep pushing for completion of a new bridge within two to three years.

Coromandel MP Sandra Goudie said the dramatic growth in traffic meant there was no room for delays between design and construction.