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Campaigners for walking and cycling across Auckland Harbour Bridge are considering a protest march and ride after the Transport Agency allegedly deemed their cause a "dead horse".

Getacross Campaign leaders intend asking the 10,051 people who have registered online backing walking and cycling links to consider a more visible show of support.

"We'll be asking them to support taking protest action because we are so disappointed with the Transport Agency's attitude," spokesman Bevan Woodward said after attending a briefing on Friday with the agency and Auckland Regional Transport Committee members.

"It was abundantly clear they [the agency] have a closed mind on this matter - they called it a dead horse, and it's not."

The agency's northern director, Wayne McDonald, denied being the first at the meeting to use that term but acknowledged confirming its aptness after Mr Woodward asked him whether he believed the campaigners were "flogging a dead horse".

He said that question followed a more technical explanation he had given for the agency board's decision not to apply in the next three years for funding for walking and cycling links on the bridge's clip-on structures.

"I said in the next three years - that did not preclude it forever."

Mr Woodward envisages a possible protest march and cycle ride across the bridge - possibly on a Sunday morning.

Agency acting regional manager Tommy Parker said the board's decision not to apply for funds for links followed technical advice that the extra "deadload" from structures such as concrete barriers and a 1.2m wide addition to the clipons would reduce their economic life by about 10 years.

The clipons are in the midst of a $45 million structural strengthening project and Mr Parker said that with careful management the agency should be able to make them last for 40 years before an alternative harbour crossing would be needed or the clipons replaced.

Mr Parker said it might be possible to allow heavy trucks back on the outside clipon lanes once the strengthening project was completed in 18 months, and to avoid reimposing restrictions on those for five to 15 years without compromising the structures' economic life. He said that would not be possible if a cycleway and walkway were built on respective sides of the clipons.

Regional transport committee chairwoman Christine Rose disputed that, saying: "It is not a credible argument that walking and cycling are the straw that could break the camel's back." She accused the agency of reciting "a litany of excuses" for not sharing the bridge with walkers and cyclists.

Mrs Rose and regional council chairman Mike Lee are also annoyed that a request they made on December 10 for one lane of the clipons to be offered to walkers and cyclists on a trial basis at weekends and public holidays to test demand was not referred to a meeting of the Transport Agency's board last week.