Congestion in London's central business district got so bad people joked that in the 1890s, the average speed by horse and buggy was about 12 km/h (8 mph). And, in 2002, the average speed was still 12 km/h.

In 2003, as congestion laid siege to his city, Mayor Ken Livingstone took a bold step and instituted cordon pricing. The concept: Reduce traffic into and out of a crowded 16-square-mile section of downtown London during business hours by charging a toll.

Instead of tollbooths, however, London is using a form of cashless tolling — digital cameras perched on sign gantries overhead, which snap license plate photos as vehicles pass underneath. Within a few days, the vehicle owner receives a bill of $8 to $13 (U.S. equivalent) per trip.

Results within London's cordoned zone were extraordinary:

• Congestion decreased 21 percent.

• Traffic speed increased 25 percent.

• Traffic delays decreased.

• Air quality improved.

• Bus ridership increased.

• Major London companies reported congestion pricing had not hurt their businesses.

For Fiscal Year 2007-2008, the program generated the U.S. equivalent of nearly $224 million in net profits, which went toward improving the city's transportation. Claiming the experiment a success, the city doubled the cordon zone in 2007 and reduced the enforcement period by one hour to offset the change.

Cashless tolling using electronic and video technologies have eliminated the need for tollbooths, making the once impossible idea of tolling city streets entirely possible. No additional right-of-way is needed — just erect an overhead gantry with a video camera.

As a result, several U.S. tollroads have converted to cashless tolling, including Miami's State Route 836; Houston's Westpark Tollway; Dallas' President George Bush Turnpike and Denver's E-470.

Each respective toll agency has converted all of its facilities to cashless systems, and many other toll agencies are exploring the conversion to cashless, as well as some U.S. cities that are interested in cashless congestion pricing.

Nice benefits package

Those U.S. cities interested in congestion pricing are discovering, as London has, that it can do more than unclog vital arteries. Cities that implement full-blown congestion pricing programs will sport a different look and feel; they will have:

• Money to invest in transportation infrastructure. These days, cities don't have many options. Their transportation infrastructure is aging and their single-largest source of funding, the gas tax, is drying up. Congestion pricing provides an additional and desperately needed revenue stream.

• The ability to vary pricing. Cashless tolling gives cities the flexibility to change toll rates according to demand and shift traffic patterns. During peak demand, the toll goes up to thin out the herd and keep traffic flowing. When demand drops, the toll goes down to encourage use. The concept is called variable pricing. It's the same theory utilities use. If you've ever paid an electricity bill, you know all about it.

• Increased mass transit use. Motorists who don't wish to pay the toll will discover they can avoid it by taking advantage of the city's transit system.

• Cleaner air. Less gridlock means less idling and, consequently, lower emissions. Ask any major city straining to stay in compliance with federal air quality regulations - that's huge.

As cities reach into their pockets for transportation funds and pull out nothing but lining, revenue-generating, congestion-busting options such as congestion pricing are going to become increasingly attractive. Look for one coming soon to a street near you.

Sources:U.S. Department of Transportation; Environmental Defense Fund; The Institute for Transportation and Development Policy and Transport for London.