New bus shelters being built on Karangahape Rd risk becoming a $2 million-plus set of public toilets, says a union leader who represents bus drivers.

Auckland Tramways Union president Gary Froggatt believes a narrow pedestrian passage behind the shelters will be a dangerous place to walk and a standing invitation to drunks to empty their bladders.

"You're going to get the low life hiding behind there, creating a security risk, and it looks absolutely appalling, these bus shelters in the middle of the footpath."

Mr Froggatt said he was concerned about the safety of his members, and called the replacement of the old shelters on Karangahape Rd's bridge over the central motorway junction "an absolute waste of ratepayers' money".

"All they needed was a bit of cleaning and tidying up," he said of the old structures, which have been there for more than 40 years and are notorious for antisocial behaviour by nightclubbers and others.

The new shelters would become "a very expensive toilet".

Auckland Transport says canopy support columns for the shelters it is building for $2.1 million in time for the Rugby World Cup have been set 3.8 metres back from the kerb on each side of the road.

That has left a 1.8m gap for pedestrians between the rear of the shelters and the edge of the road bridge.

The old structures spanned the entire footpath on each side of the road, with bus stop seats set back to the edge of the bridge, leaving a larger space for pedestrians to walk past.

But Auckland Transport spokeswoman Sharon Hunter expects the area in front of the shelters to be the main pedestrian thoroughfare except when passengers queue to board buses.

"Then pedestrians will most likely choose to bypass it by using the available width behind the shelters," she said.

Ms Hunter said that if people chose to walk behind the shelters, they and anybody they might encounter would be seen easily through clear security glass.

The old structures were at the end of their life, as demonstrated by pieces of their barrier screen falling away "at semi-regular intervals", posing a risk to motorway traffic below.

"Also, the old shelters, being fully enclosed, provided an environment which contributed to less desirable behaviour."

But Mr Froggatt said pedestrians had more room to avoid trouble with the old shelters.

"Before, it was open - it was okay to walk through - you could see the buses coming.

Now, with individual shelters in the middle of the footpath they're going to prove a big obstruction."

Business association manager Barbara Holloway said she was pleased with the design of the new shelters, which had passed a police safety audit.

She said their clear glass panels would give pedestrians better views from the bridge, and there would be gaps in the passage at the back so people could evade any trouble.