The city of London launched a bold experiment last week to nudge drivers of private cars onto public transport. It started charging drivers $8 a day to enter the city center during weekdays.
So far, it's working well. Traffic congestion is down about 20 percent. Pollution is less, pedestrians are safer, and the city will have more money to improve railways. The system works by having hundreds of cameras read the license plates of cars entering the city. Computers then check the numbers against a list of people who have paid the fee.
Highway tolls are nothing new. England imposed its first toll in 1270 to pay for a road. And smaller urban areas in Norway, the Netherlands, and Singapore have proved that a "congestion tax" can work.
But London's experiment shows that even the world's big cities need not fear the logistics of tracking cars.
The city's left-wing mayor, Ken Livingston, picked up the idea of a congestion tax from a paper by conservative American economist Milton Friedman, who's famous for designing market mechanisms for public policy. Mr. Friedman wrote: "The people who drive on a road should be charged ... in proportion to their use of the service."
Mr. Livingston deserves credit for pushing a scheme that had many critics beforehand but is working to solve one of the biggest problem facing Londoners: clogged streets.
US mayors with traffic jams should visit London soon to see if this idea can be brought back to car-obsessed America. Some US cities already use garage taxes or tunnel and bridge tolls to restrain urban car use and avoid building new roads. But that's not enough to keep big cities livable.