A 19th Century Tech Still Going Strong in the 21st

Once they were a common mode of public transportation in cities around the world. Nowadays, you'll only find working cable cars in San Francisco.

Beginning in the late 19th century, the cars--which replaced horse-drawn cars and were capable of climbing even the steepest hills--were a main way to get around here. At one time there were eight lines, all run by private companies, and it was only much later that those lines were bought up by the city of San Francisco.

Today, there are three lines in San Francisco, all of which run out of a single barn near Chinatown. Seen here, the Powell and Market line carries a carload of riders east along Washington Street.

CNET's Daniel Terdiman swung by San Francisco's Cable Car Museum to see how the city's world famous vehicles--the only ones remaining in operation in the world--work. You can read his full report here.

Cable cars await their turn at the turnaround.

Although the 1906 earthquake was a disaster, it may well have been the ensuing fire that caused the most damage to the city. Seen here: the remains of a cable car barn and the cars inside. All that remained was rubble and the metal trucks of the cable cars.

The effect of the earthquake on the building that houses the cable car carbarn and powerhouse, and the Cable Car Museum. The quake put an end to many of the private cable car lines in the city.

Each of the four cable lines has a corresponding set of three sheaves in the carbarn attached to the museum. The three are known as an idler sheave (the closest set of wheels), a driving sheave (the second large set of wheels on each line), and a tension sheave (the furthest back). These three sheaves are used to move a single loop of cable through the underground channels.

According to the museum, "each cable has its own electric motor, which turns the driving sheave by means of a gear reducer. Each gear reducer contains three pairs of gears, which allow the sheave to turn at a slower speed than the motor.

The driving and idler sheaves work in conjunction to move the cable under the streets. The motor powers the driving sheave, which moves in the opposite direction from the idler sheave, which offers more surface contact for the cable, according to the museum. "As the cable loops in a figure-eight pattern, there is more friction on the cable, and the friction between the cable and sheaves allows the cable to move."

Though the powerhouse runs on electric power today, from 1886 until 1911, it was powered by steam engines, according to the museum.

These are the tension carriages for the four lines. They ensure that the cables are always taut and actually move on their own tracks to make sure they can take up the slack depending on the number of cars in use and the number of passengers riding those cars.

This is the "crown jewel" of the Cable Car Museum, an original 1873 Clay Street Hill cable car. This is the only one remaining in the world that uses the original grip system created by cable car inventor Andrew Halladie.

Halladie's father had patents on wire rope cables, and the younger man began testing a new system on August 2, 1873, that incorporated equipment he'd developed in order to haul gold ore from mines during the Gold Rush.

An original cable car trailer, No. 62.

Although the Cable Car Museum maintains some original cable cars, it also has a selection of scale models depicting the many uses for the cars.

This model is of the Market Street Cable Railway Company's railway post office car, from the 1890s.

"During the late 1890s, the U.S. Postal Service, in cooperation with various railway companies, developed the 'railway post office car.' RPO cars were in service long before the use of trucks or other vehicles to deliver mail. These cars performed several jobs, including mail delivery and collection from mail boxes and in-route mail sorting. Pedestrians were able to flag down an RPO car and drop mail into the slots provided on either side of the car."

Today, San Francisco maintains three cable car turnarounds, where the car drives onto the table, which spins around, allowing the car to grab the cable and move onto the opposite direction track. This is the Aquatic Park turnaround, which is officially known as the Friedel Klussmann Memorial Turnaround, after the woman who spearheaded efforts by city leaders and businesspeople in 1947 to save the cable cars from retirement.

There are 28 Powell Street cable cars, each of which has a single open trailer. These are slightly smaller than their California Street cousins. They are 27 feet, 6 inches long, 8 feet wide, and weigh in at 15,500 pounds. They can hold 60 people, with up to 29 sitting.

In the old days, cable cars were often actually two separate cars, a dummy--the locomotive--and a trailer. Today, the dummy and the trailer are combined into a single car.

Here, we see two cars, Sutter Street Dummy No. 46 and Trailer No. 54. No. 54 used to be pulled by horses before the mechanized dummies came along. In addition, the trailer was featured in the 1938 San Francisco World's Fair on Treasure Island.

This is a map showing the breadth of the cable car system--operated by nine companies--in 1893.