This contributes to gridlock: many single-occupant vehicles idle en route, adding to travel times and smog.

But the convenience of a single-occupant vehicle is fast disappearing, she said.

In New York, restrictions were placed (and later eased) on single-occupant vehicles entering Manhattan after the Sept. 11 terrorist attacks.

When it reopened on October 15, 2001, strict new regulations were enacted banning single-occupant vehicles and trucks from entering the tunnel.

Because you're carpooling with a neighbor, you are allowed on the Turnpike, where single-occupant vehicles have been banned for years.

The system, being tested in California, gives drivers of single-occupant vehicles the option of paying for the right to drive in the reserved lane.

The programs promote alternatives to the single-occupant vehicle.

The Honda Gyro is a family of small, three-wheeled, single-occupant vehicles sold primarily in Japan, and often used for delivery or express service.

In order to achieve greener transportation, Cornell wants to reduce its employee use of "single-occupant vehicles" by 25 percent within 15 years.

Another would ban single-occupant vehicles.