Auckland Council transport chairman Mike Lee has made a caustic attack on the Transport Minister on his blog for refusing to accept the case for a central city rail tunnel.

Case findings from a $5 million study commissioned by KiwiRail and the former Auckland Regional Transport Authority predicted a $2 billion tunnel in central Auckland would pay for itself more than three times over.

Transport Minister Steven Joyce yesterday said the report had raised "many unanswered questions", which needed to be clarified before taking the project to the next level.

Mr Joyce is questioning, among others, the inclusion of "transformational" benefits the experts say will provide extra productivity and concentrated urban development to justify an early construction of the 3.5km tunnel to stretch from Britomart to Mt Eden.

Mr Lee said: "The National Government would dearly love to kill it off - but if they are not careful, what comes roaring out of Auckland's underground rail link could end up running down the National Government."

He said many public transport advocates have found Mr Joyce to be "something of an enigma" and that his "roads first" and "pro urban-sprawl" views were "fairly basic small-town red neck stuff".

In the blog, Mr Lee compared Mr Joyce to former National Minister of Works Stan Goosman, who cancelled Auckland's rail plans in the 1950s.

"Not only is there an echo of events, but also of personalities, with Steven Joyce the present-day 'minister for everything' playing the role of the 1950s era National 'minister for everything' Stan Goosman," he wrote.

"In the late 1940s, the Ministry of Works formulated a scheme which was accepted by all parties ... before being killed off by the National Government of the time. Again in the late 1960s, the ARA and NZ Railways worked up another plan, this was in turn killed off in 1975 by the National Government."

Mr Joyce denied the Government was out to kill the project, but said the $2 billion plus price tag was part of the reason the project would not get his blessings for a quick start.

"The cost is massive. Given the sheer volume and size of it, we surely need a little more critical analysis," he said.

"Already Ministry of Transport officials have sat down to look at the report, and Auckland Transport and Treasury will want to have a look as well to get some clarity on some of the issues that have been raised."

He said major road and rail projects will finish between 2013-2015, and this Auckland rail tunnel could be the next "big project", with the third harbour crossing.

"The next question beyond that is who pays and how does Auckland afford or make up its contribution?" said Mr Joyce.

"A number of things have been ruled out, such as rates and that sort of thing, but not much have been ruled in."

"In the next four to five years, the Government quite clearly doesn't have an extra $2 billion to put to it."