Berlin, Cologne, and Hanover have all decided to implement a neat way to make sure that their air is cleaner than other cities by using stickers. Drivers will have to buy stickers that denote how much pollution their cars emit and will be charge accordingly when driving in designated environmental zones. This is such a neat and simple idea.

Drivers now have to display a coloured sticker on their vehicle to enter the inner city zones. The colour depends on the pollutants the vehicle emits.

The cities are gradually phasing in fines of 40 euros (£29;$58) for anyone caught driving without a sticker.

Other German cities – but not all – plan to have such zones later in 2008.

The stickers – green, red or yellow – are mandatory not only for locals but also for foreign drivers, including tourists.

There is a one-off charge of five to 10 euros for the stickers, issued by Germany’s vehicle registration authority and authorised garages.