SYDNEY has been ranked at the bottom of a list of the world's most important 20 cities for the quality of its transport infrastructure, behind Mumbai, Sao Paulo and Mexico City.

With no underground metro, a shortage of taxis and worsening congestion, Sydney fell short of its international peers according to the Cities of Opportunity report, compiled by the New York Chamber of Commerce and PricewaterhouseCoopers.

The report comes after the NSW Government slashed its promised spending on transport infrastructure in its November mini-budget, and after new figures from the state's audit office showing Sydney's traffic congestion has deteriorated over the past four years.

"Why would investors be attracted to Sydney if we can't get basic transport infrastructure right?" said Patricia Forsythe, the executive director of the Sydney Chamber of Commerce.

"Other global cities have shown only one path for an efficient transport network, and that is metrorail. We've got to invest now so that we don't have a mobility crisis in the future."