Richard B. Mckenzie writes on the law of unforseen consequences:

In 2006, the California legislature authorized the state Department of Motor Vehicles to distribute 85,000 stickers to the owners of gasoline-electric hybrid cars. The stickers allow drivers to travel without passengers in all of the state's high occupancy vehicle (HOV) lanes, which were formerly restricted to cars with two or more passengers. A report determined that California's HOV lanes were operating only at two-thirds of their capacity and not easing congestion as much as they could; the idea was to stimulate demand for hybrids and thus reduce the emissions of greenhouse pollutants.

The sticker distribution did exactly what it was supposed to do. People wanted to shave time off their commute, and the stickers drove up demand for hybrids for the Toyota Prius and Honda Civic hybrid (the only cars that qualified for stickers), so much so that the small Prius has been selling for over $30,000, and until recently had waiting lists. The Civic hybrid has carried a dealer "added premium" to the manufacturer's suggested list price of as much as $4,000 (with the hybrid Civic total price nearly $7,500 higher than the quoted price of a non-hybrid Civic).

But it seems that the hybrid HOV program, rather than suppressing automobile use, did the exact opposite: The program was wildly popular, and the HOV lanes became clogged. Californians began talking about "Prius backlash."

Then at the end of January, the DMV ran out of stickers, leaving more than 800 new Prius and Civic hybrid owners, who may have been enticed to buy their hybrids at premium prices inflated by sticker advantage and who applied for the stickers, without the right to drive alone in the state's HOV lanes.