Auckland Transport is being tight-lipped about whether Serco's fall from grace as a prison manager will harm its chances of running the city's passenger trains.

On top of its contracts to run two Auckland prisons, the multinational service company is one of three bidders short-listed by the council body, to manage the trains from July next year.

The others are KiwiRail and the existing operator, Transdev, which has run Auckland's rail fleet under various names since 2004.

An Auckland Transport spokesman said this afternoon that for "probity" reasons, it would not comment on Serco's chances of winning the new contract, which is likely to be worth more than 60 million dollars a year.

However, he added that Serco's various divisions across the globe were operated "quite independently of each other".