From Wikipedia, the free encyclopedia

A lift hill, or chain hill, is often the initial upward section of track on a typical roller coaster that initially transports the roller coaster train to an elevated point. Upon reaching the top, the train is then disengaged from the lift hill and allowed to coast through the rest of the roller coaster's circuit.

Lift hills usually propel the train to the top of the ride via one of two methods: a chain lift involving a long, continuous chain which trains hook on to and are carried to the top; or a drive tire system in which multiple motorized tires push the train upwards.

The Cable lift is a type of lift mechanism that was used on many scenic railway-style coasters, which were built in the early part of the 20th century. Several still exist today and still use the mechanism. This type of lift has returned for Cedar Point's Millennium Force and La Qua's Thunder Dolphin, and is used on the wooden roller coaster El Toro at Six Flags Great Adventure. The cable lift utilizes a cable loop in place of the traditional chain, which is attached to a short section of chain that engages the train's chain hook. Because a cable is much lighter than a chain, cable lifts are much faster than chain lifts and can be used on much steeper hills - even vertical. A cable also requires far less maintenance than a chain. Another advantage to park guests is that a cable lift is very quiet, partly because the main drive winch is located directly beneath the top of the lift, a location which will normally be relatively far from guest-accessible areas. However, one minor disadvantage of a cable lift system is that it must return to the bottom of the lift hill after lifting each train, which does not apply to a continuously moving chain lift.

Diagram depicting the anti-rollback safety feature.

The familiar "clickity-clack" sound that occurs as roller coaster trains ascend the lift hill is not caused by the chain itself. The cause for this noise is actually a safety device used on lift hills -- the anti-rollback device. The anti-rollback device is a standard safety feature, typically consisting of a continuous, saw-toothed, section of metal, forming a linear ratchet.

Roller coaster trains are fitted with anti-rollback "dogs" which are essentially heavy-duty pieces of metal which fall and rest in each groove of the anti-rollback device on the track as the trains ascend the lift-hill. This makes the "clicking" sound and essentially allows the train to go upwards only, effectively preventing the train from rolling back down the hill should it ever encounter a power failure or broken chain.

• CoasterQuest.com - How a roller coaster is propelled