Rollback (roller coaster)

A rollback occurs on a launched roller coaster when the train is not launched fast enough to reach the top of the tower. It will roll backwards down the tower, and will be stopped by brakes on the launch track. Any roller coaster on which it is possible for a rollback to occur will have these brakes. Intamin, a manufacturer of roller-coasters, refers to the 'rollback' as a 'short shot.'

Most coasters contain at least one anti-rollback device to prevent a train from rolling backwards while ascending the main lift. This is typically with chain-driven lifts, not hydraulic launchers such as Kingda Ka or Top Thrill Dragster.

Rollbacks are most common (though still quite rare) on the world's two largest launched roller coasters, "Kingda Ka" at Six Flags Great Adventure and "Top Thrill Dragster" at Cedar Point. Because of improved technology, Kingda Ka rolls back significantly less often than Top Thrill Dragster.

There are several factors that can cause a rollback:
* Unusual wind gusts could slow the train down enough to cause it to roll back.
* Cold weather increases friction in the wheels.
* A rollback will often occur during the first few test launches each day, as the launch motor has not been sufficiently warmed up by this point. Intentional rollbacks are sometimes conducted during testing.
* Fewer passengers on the ride reduces the momentum and could cause a rollback.

While the general public may not realize that rollbacks usually are completely safe and that coasters are designed with them in mind, many coaster enthusiasts look forward to being in one. Being in a rollback essentially gives riders a ride and a half, as the train will be launched again after the rollback (although, when a rollback occurs with people on the train, it will first be brought back to the station to give the guests the option of getting off the ride). This is less of an incentive in parks that charge an overall admission fee and don't charge for individual rides.

In [http://www.youtube.com/watch?v=tlHDDzfP4_4 a video of a rollback] on Stealth at Thorpe Park, the train is seen to reach slightly over halfway over the midpoint at the top. The train proceeded to roll back, due to an insufficiently powerful launch, combined with an uneven distribution of weight on the train in April 2006. Stealth also had a rollback in March 2008 due to strong winds.

Very rarely, a train is launched with just enough speed to reach the track's highest point, resulting in the train getting stuck on the top. This results in neither a full ride nor a rollback. This happened once on Top Thrill Dragster, and a ride mechanic had to take an elevator to the top, and give the train a small push so it could complete the ride. [http://www.xtremecoastin.com/videos/misc_videos/ttdstuck_2005.htm] It has also happened on Stealth at Thorpe Park during early morning tests.

External links

* [http://www.youtube.com/watch?v=ylsj4BvnGB8 On-ride footage of a rollback on Top Thrill Dragster]
* [http://www.youtube.com/watch?v=oNYzj6tw7XA Footage of a rollback on Kingda Ka]
* [http://www.youtube.com/watch?v=LeOEZqbCjzQ Footage of Top Thrill Dragster stuck in 2005]