In August 2007, New York City Mayor Michael Bloomberg made an announcement that was, at the time, thought to be the beginning of a congestion pricing program for the city. "Congestion throughout New York City is clogging our streets, polluting our air and restricting our economy," Bloomberg said, "and the time to do something about it is now."

Just five months later, in January 2008, the proposed plan -- under which an $8 charge would be levied on motorists driving into lower Manhattan -- died, as the state Senate and Assembly failed to act before a federal traffic relief grant application period expired.

But a handful of cities are proving that such a pricing scheme not only reduces the amount of traffic congestion, but also raises money and reduces pollution -- though it does often come with controversy from the public. Still, congestion pricing is intact in Singapore, London, Stockholm and Milan -- and here's what the research shows about how effective it is:

Congestion+Charging+Infographic

Infographic produced by Liam Fisher and Car Finance 24/7.