One of the biggest risks in building the $3.4 billion City Rail Link will come towards the end when operating systems are installed - something that potentially could cause lengthy delays and extra costs.
The project's chief executive Dr Sean Sweeney says the real challenge of New Zealand's largest infrastructure project is not in building the tunnels or stations but in the systems for controls, signals and safety which are added at the end.
He cites system problems with London's $30b Crossrail project that delayed works for three years and added an extra $5b as an indication of where the greatest complexity and risk lies for the CRL.
Sweeney was speaking as the Herald begins a six-day series on major projects in Auckland, ranging from transformation of Wynyard Quarter for the America's Cup, a $1.8b rebuild of Auckland Airport, the redeveloped Westfield Newmarket and the delayed Convention Centre and Commercial Bay builds.
The CRL dwarfs all these projects. It eclipses New Zealand's major dam-building projects, such as the Clyde Dam, says Sweeney, an engineer who has worked on Te Papa and major public infrastructure projects in Melbourne and Sydney.
All going well, Sweeney says the successful bidder and final price for the CRL will be known in May. Once that's confirmed, work will begin later this year building the main sections of the tunnels and two new stations along the 3.5km underground route from Britomart to a new above-ground station at Mt Eden.
The first leg of the CRL, cut-and-cover trenches busting through Britomart and up Albert St to Wyndham St, is on track to be finished by the end of this year.
In January, the Herald reported the cost of the CRL - expanded to include a second entrance at the new Karangahape station and longer platforms to increase capacity - was expected to increase by $500m and there are fears it could exceed $1b.
Sweeney, Auckland Council and the Government who are joint funding the CRL, will not comment on the cost until the final bidder is announced.
Sweeney, who thrives on a challenge - "it's a weird affliction" - says all the experts he has spoken to have told him the really difficult bit with the CRL is not building the tunnels and stations but the back-end rail systems.
The systems for controls and signals, safety and fire just cannot be installed in a clean tunnel. They have to be tested to work safely in a multitude of states and operating systems.
"The system is bespoke because it is connecting into a live operating network and no-one can foretell or foreshadow the complexity of doing that. It is vexing our minds."
Sweeney says it is far more complicated than the systems for the Waterview tunnel and the problem is made worse because New Zealand has never built a metro rail system.
He said City Rail Link Ltd, the company set up by the Government and council to oversee the project, would be idiots not to look at Crossrail.
"The Crossrail project from the minute I walked into this project was chartered and chronicled as the benchmark of how things should happen. It was an exemplar and they did so many things so well," said Sweeney, who took over the reins for the CRL in July last year.
The Crossrail chairman was knighted and everyone was doing victory laps, said Sweeney, until last August when they signalled a little delay, that became a little bit longer.
Then the board and chief got sacked and now they are talking about a three-year delay and cost overruns of $5b, he said.
The Government and council are currently developing a "risk register" for the CRL based on 12 "high" and "critical" risks primarily based on the consequences of something happening, rather than the likelihood.
The risks include delays due to operational issues, increased costs and losing the confidence of Aucklanders.
• Today: City Rail Link
• Tuesday: International Convention Centre
• Wednesday: Newmarket shopping centre
• Thursday: Auckland International Airport
• Friday: Commercial Bay
• Saturday: America's Cup Village Development