A couple of interesting statistics that may help identifying least/best managed traffic among mega cities. It seems like mega cities in emerging markets such as Johannesburg, Sao Paolo, Mumbai/New Dehli are consistently rated least managed and public transportation heavy Paris, Tokyo and London are rated best managed.
Commuter Pain Index
PwC 2010 Cities of Opportunity Study - Transportation Ranking.
Best: Paris, Chicago, London, Tokyo and Beijing
Worst: Johanesburg, Sao Paulo, Mumbai, Toronto and Santiago
Transport-related Energy Consumption Gigajoules per capita per year
Worst: Houston, Phoenix, Detroit, Denver, LA, SF, Boston, etc..
Best Commute In US Cities
Among large metro, Pittsburgh, New Orleans, Portland, Cincinati, Philadelphia, Boston and Detroit are ranked high