The congestion charge was originally pushed as a means of discouraging people from driving into the crowded central area of the city. However, recent studies have indicated that in spite of the fee, traffic has actually gotten worse in London. More recently, Livingstone has moved to expand the congestion zone and change the fee structure to make it based carbon dioxide emissions of the car. As a result cars that emit less than 120g/km of CO2 would have been exempt from the charge while the thirstiest vehicles would have seen the fee rise to as much as £25 per day. Johnson, the new mayor is opposed to this emissions-based fee and promises to scrap the plan and possibly even rescind the expansion of the congestion zone that occurred in 2007. So it looks like while other cities will proceed with emissions based congestion charges, the city that pioneered the idea may be taking a step back.