Jarrett Walker was a consultant on the initial stages of the Auckland and Wellington bus network redesigns

A public transport expert involved in bus network redesigns says things have turned out "very differently" in two of New Zealand's largest cities.

Jarrett Walker is an internationally renowned consultant on public transport issues and was involved in closed door sessions that started the ball rolling on bus network redesigns in Auckland and Wellington.

Changes in both cities hit potholes but Wellington's problems have been so severe the Greater Wellington Regional Council was forced to acknowledge problems with at least 30 bus routes on the new network.

Walker will be speaking at the Grand Millenium Hotel in Auckland on Thursday night, part of 'Auckland Conversations', a discussion series on big picture city issues.

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* Overcrowded, unreliable buses follow service changes on Auckland's North Shore

* At least 30 Wellington bus routes need fixing as network continues to struggle

* How did transport planners get Wellington's new bus network so wrong?

The US-based public transit consultant is quick to distance himself from GWRC and said he has "had no role in Wellington at all since 2012".

CALLUM MCGILLIVRAY/STUFF Rapid buses are a key feature of any network redesign, Walker says.

"I last worked in Wellington six years ago on a very early version of this plan, my understanding is that some fairly basic mistakes have occurred."

But he had great praise for Auckland Transport who he periodically provided advice to in the years afterwards.

"I just want Auckland to understand and appreciate what has been achieved there."

He is likely to face questions on bus network redesigns which have been rolled out across both Auckland and Wellington.

Walker's reply to most of those queries is likely to be: "Redesign work is difficult".

"It's difficult politically because people always complain when you change anything."

MONIQUE FORD/STUFF GWRC said at least 30 routes needed to be fixed after the changes.

And New Zealand had the added complication of a slew of private operators on its public bus networks, all primed to treat one another as competitors, Walker said.

"It's a whole lot of work so the idea has to be so great that it's worth going through all of that," Walker said.

"I think it is."

That idea is to move bus networks away from a system transporting people from suburb-to-CBD to an interlocking grid pattern of rapid and frequent bus routes that can take you anywhere.

"I give Auckland Transport a lot of credit for having not rushed the implementation but for having done it slowly and carefully and really really well so that we haven't seen the kinds of hiccups that we've seen in Wellington."

People might have to take two buses, or a bus and a train, but their overall trip time should be shorter due to reduced wait times, Walker said.

But Auckland's network may not be as rapid or as convenient as promised either.

Yesterday North Shore bus commuters complained to Stuff about chronic overcrowding and a bus service with worsening reliability after network changes went through.

Walker said some concerns with Auckland's redesign "may be valid" as well, but the causes were often in the implementation not the design.

Redesigns could come unstuck if bus operators weren't on-board with plans for more rapid buses, if bus stops weren't maintained well enough, or if traffic prevented buses from being rapid at all, Walker said.

"My job is never to pretend that it's easy, my job is to build an understanding of why, even though it's difficult, you can get such great outcomes that it's worth doing."