Auckland Mayor Len Brown has seized on pollution from diesel buses as ammunition for early government funding of a $2.86 billion underground railway.

He told a rail industry conference in the city yesterday that the project, to which the Government has promised to contribute half the cost but not until 2020, was needed to combat rising pollution from more buses streaming into central Auckland.

"Unless we get the City Rail Link [CRL] in place, take stress off our bus lanes, give our communities greater access to the rail network ... we are going to see higher levels of pollution in our downtown area as we have to feed more buses on to congested roads," Mr Brown said.

A study by the National Institute of Water and Atmospheric Research with scientists from the University of Auckland and AUT University found that air at the bottom of the Queen St valley risks failing World Health Organisation standards designed to prevent respiratory and heart disease.


Customs St, used by hundreds of buses a day, was found to have the highest nitrogen dioxide diesel vehicle emissions among 62 city sites despite being within 200m of the waterfront and its sea breezes.

The Government has agreed to consider accelerating the rail project if Auckland can prove train patronage will increase to 20 million annual passenger trips by 2020 and that 22,000 new central city jobs will be created.

Mr Brown said an increase from 8m to 11.2m trips over the past four years showed "we are right on line" to meet the patronage target, but the employment goal was more problematic.