VOA常速英语:Ever Seen a Mountain Goat on Wheels?

The charming city of San Francisco, California, is world famous for its cable cars. As one song puts it, they climb halfway to the stars up the city's steep hills and down again. Each open-air car seats 30, but tourists, especially, love to grab a strap, hang on for the ride, and hop off when they feel like it.

The job was once handled by ordinary streetcars, pulled by horses. But they struggled to get a foothold, especially in wet weather. Electrifying them did not help. They simply could not get enough traction on San Francisco's 42 steep hills, some of which have a 30-degree gradient or more.

Then, in 1873, a fellow named Andrew Halladie suggested attaching streetcars to a moving cable buried in a trench below ground. When the operator chosen for the test run took one look down the hill ahead, he jumped out and ran away. So Halladie made the run, and a unique mode of transportation was born.

Powered by giant motors and wheels in a central location, three heavy wire cables the size of your arm run up, down, and around San Francisco in continuous loops. Even when there's no cable car in sight, you can hear the moving cables whirring beneath the street.

The cars themselves have no power other than a little generator that runs their headlights and overhead bulbs.

When it's time to move forward, the operator - or gripman, as he's called - pulls a lever, and a pincer-like device beneath the car grabs the moving cable like a pair of pliers. The car moves ahead at a modest 15 kilometers per hour. To stop, the gripman lets go of the cable, the car coasts for awhile, and brakes are applied.

There are never runaways, because cable cars have three types of braking. Most accidents happen when automobiles run into them.

Los Angeles; Chicago; Washington, D.C.; and cities in Europe and Australia once had cable-car systems as well. But they're all gone. San Francisco's is the last.?

In 1947, the mayor proposed shutting down the system as too slow, but San Franciscans howled in protest. Now it's written into law that the hilly city by the San Francisco Bay MUST keep its moving treasures.