Why do traffic forecasters get it so wrong?

In the case of the Lane Cove Tunnel, which opened in 2007 with about a third of the predicted traffic volumes, the Supreme Court heard one suggested answer on Monday: forecasters come up with traffic figures based on their business needs, not what happens on the road.

Lane Cove Tunnel.

Those figures are coming back to hurt the forecasters, two of the biggest names in the business, that are facing a $144 million lawsuit by aggrieved investors.

AMP Capital Investors, the manager of two funds that lost when the tunnel went into receivership within three years of opening, is suing Parsons Brinckerhoff and Booz Allen Hamilton, both of which have since won numerous lucrative contracts from the state government.