More from the impossible-is-catching-on-department. San Francisco is studying the idea of charging motorists fees—often called congestion pricing–for driving on some of its most-congested roads at peak hours.  The city has been inspired in part by London’s successful example, which mayor Ken Livingstone, in town for World Environment Day, has been talking up: Congestion has decreased some 30 percent—or 50,000 cars—in central London since pricing was implemented two years ago. (Many other cities are also discussing variations, such as HOT lanes, on the congestion pricing  model.)

Meanwhile, Great Britain is considering something more ambitious yet: a national road-pricing scheme that would use satellite and GPS technology to make drivers pay by the mile to use the most-congested routes.

  • The plan to win British motorists over includes reducing road taxes and "petrol duty" in favor of charging drivers for each mile they drive on certain targeted routes. Charges would vary according to distance traveled, time of day, and congestion.

    The principle behind road pricing (and similar ideas, such as pay-as-you-drive car insurance) is to make the price of driving more closely reflect its social and environmental consequences—such as collisions, pollution, and congestion.

    In the process, it makes owning a car less like an all-you-can-eat buffet and breaks the large fixed costs into smaller, pay-as-you-go charges—increasing the incentive *not* to gorge.