The Basin Reserve flyover design team was "technically intrigued" by the prospect of developing the alternative known as Option X instead, but they could not make it work.
Wayne Stewart, who oversaw development of the proposed $90 million flyover, has defended the effort made by the New Zealand Transport Agency to come up with different solutions to the Basin's congestion woes.
He told a four-member board of inquiry today that numerous solutions had been evaluated and re-evaluated over the past 12 years, and every time the flyover had surfaced as the best option.
The board is considering the agency's resource consent application to build a two-lane highway flyover, 20 metres north of the historic cricket ground. The two-month hearing is into its third week.
Dr Stewart addressed criticism from the Architecture Centre that the agency did not do enough to develop its Option X proposal, which involves directing all local traffic to the west of the Basin along Sussex St and turning Buckle St into a tunnel that would run underneath.
The agency actually came up with a similar idea, known as Option E, a year or so before Option X was first mooted in 2011, Dr Stewart said.
"I was responsible for creating the Option E concept and my interest in finding such an option was reignited when I saw Option X," he said.
"I would describe the team as being technically intrigued by seeing how such an option would work."
Option X was subjected to rigorous examination, but was eventually discarded for many of the same reasons Option E was abandoned, he said.
It was too expensive, would not have been a good fit for the heritage area around the Basin, and it required demolishing private property along Sussex St in order to widen the road.
The agency reconsidered Option X in 2012 after the Government approved funding for a Buckle St tunnel, so it could build the National War Memorial Park overhead.
But after some number-crunching, it found Option X was still going to cost about $60m more than a flyover, Dr Stewart said. The Architecture Centre disputes this cost.
The agency also revisited the idea of a Basin Reserve tunnel after funding for the Buckle St tunnel was approved, but it was still going to cost at least $100m more than a flyover.
It would have also been a lot more "risky" to build given the soft soils underneath the Basin Reserve.
Dr Stewart noted that Wellington City Council did its own assessment of alternatives early last year and also found a flyover to be a better than Option X or a tunnel.
- The Dominion Post