Stockholm's congestion tax

http://www.stockholm.se/PageFiles/70349/Sammanfattning%20eng%20090918_.pdf

This report details the findings of Stockholm's decision to implement a congestion tax on vehicles entering the city from
beyond a cordon during certain hours, similar to that in London, England.

C02 emissions fell, transit ridership increased, and low-emission vehicle purchases increased
(as they are exempt from the tax).