From what I've read and understand, the London congestion charge did not reduce traffic. It stayed the same and people just sucked it up, paid the charges and accepted it, just like we do with the gas prices. It might make a person think twice about driving into the city but it certainly wouldn't stop them. The congestion charge does however generate money for the city. So to go to the original source of this thread, and that being the bad air quality in the city, the congetion charge wouldn't really help.