In Madrid you can pay for free if you have an electric vehicle, do you have a hybrid car you have to 20% less. But do you have a car made in 2001 who drives on diesel you have to pay 20% more! This will all start on July 1, this way the city hopes it will ease pollution. It's now the people's choice. They can either take a bus, buy a new car or just pay full price.
This will make people think a lot more about the effects of driving. At first they will think 'what the hell' but then they will actually think about it and get to realize why they are doing this. I think people who drive electric cars are aware of whats happening with the environment and so I think it's fair that they don't have to pay and others who drive a diesel have to pay extra, because they do pollute the air more.
Future growth potential?
If all the cities in the world would things like this, or other small things to discourage people to drive their cars. It would have a big impact on the worlds pollution problem. We don't need those air clearing billboard anymore! Or well maybe a little bit ;) This will also have an effect on people's material well being because they will have to pay more or less!