Rollback (roller coaster)

Sign warning Kingda Ka riders that a rollback may occur

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 a rollback can possibly occur will have these brakes.

Most coasters contain at least one anti-rollback device to prevent the 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 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 you 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).

Very rarely the train is launched with just enough speed to reach the track's apex, resulting in the train getting stuck on the top, so it won't complete the full ride, and won't give a rollback either. This happened on Top Thrill Dragster at Cedar Point, and a ride operator had to take a elevator to the top, and give the car a small push so it could complete the ride.

Video of train with people on Top Thrill Dragster at Cedar Point standing still on the top: http://www.youtube.com/watch?v=nekzzvIicVA