Operation
The cable is itself powered by a stationary motor or engine situated in a cable house or power house. The speed at which it moves is relatively constant depending on the number of units gripping the cable at any given time.
The cable car begins moving when a clamping device attached to the car, called a grip, applies pressure to ("grips") the moving cable. Conversely the car is stopped by releasing pressure on the cable (with or without completely detaching) and applying the brakes. This gripping and ungripping action may be manual, as was the case in all early cable car systems, or automatic, as is the case in some recent cable operated people mover type systems. Gripping must be an even and gradual process in order to avoid bringing the car to cable speed too quickly and unacceptably jarring the passengers.
In the case of manual systems, the grip resembles a very large pair of pliers, and considerable strength and skill are required to operate the car. As many early cable car operators discovered the hard way, if the grip is not applied properly, it can damage the cable, or even worse, become entangled in the cable. In the latter case, the cable car may not be able to stop and can wreak havoc along its route until the cable house realizes the mishap and halts the cable.
One apparent advantage of the cable car is its relative energy efficiency, because of the economy of centrally located power stations, and the ability of descending cars to transfer energy to ascending cars. However, this advantage is totally negated by the relatively large energy consumption required to simply move the cable over and under the numerous guide rollers and around the many sheaves. Approximately 95% of the tractive effort in the San Francisco system is expended in simply moving the four cables at 9.5 miles per hour. Electric cars with regenerative braking do offer the advantages, without the problem of moving a cable. In the case of steep grades, however, cable traction has the major advantage of not depending on adhesion between wheels and rails. There is also the obvious advantage that keeping the car gripped to the cable will also limit the downhill speed to that of the cable.
Because of the constant and relatively low speed, a cable car's potential to cause harm in an accident can be underestimated. Even with a cable car traveling at only 9 miles per hour, the mass of the cable car and the combined strength and speed of the cable can do quite a lot of damage in a collision.
Read more about this topic: Cable Car (railway)
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—Francis Bacon (1560–1626)
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