London has established a “congestion charge zone” in which drivers in Central London and some neighborhoods are tolled for driving at certain times. In Boston, some people have recently floated this as a possible way of reducing congestion here.

The linked article is to a BBC story showing preliminary numbers indicating a drop in traffic volume in the affected areas since the implementation of the plan.

http://news.bbc.co.uk/2/hi/uk_news/england/london/6423349.stm