Metro rail systems such as Auckland's proposed $2.4 billion link from Britomart to Mt Eden do nothing to reduce congestion in the long run, says a visiting international transport expert.
"With metro, all you do is create extra capacity," Dr Dinesh Mohan told the Traffic Institute at its annual conference in Auckland today.
"Then, after two years, all the roads are congested again - and the metro is full.
"You just increase transport, you don't reduce congestion."
Dr Mohan, who specialises in transport safety and pollution research and has published more than 200 scientific papers, said a study from his Delhi-based Indian Institute of Technology found underground rail systems generated more carbon dioxide emissions than diesel buses when tallying up the amount of energy needed to manufacture their infrastructure.