that are separated by a piston. As the incompressible hydraulic fluid is pumped into one compartment, nitrogen in the other compartment is compressed. At launch, the fluid under pressure from the accumulators is used to drive a number of hydraulic motors (commonly 16 or 32), which spin a large winch drum that rewinds a cable attached to the lead car of the train, called the catch-car, in a matter of seconds. The cable runs under the launch track, and the catch-car moves along a groove in the track's center. The motor is positioned at the opposite end of the catch-car on the launch track. While the train inches forward into a ready position, the pusher mechanism moves back from the motor toward the train. Once the pusher connects, the anti-rollback braking system drops beneath the track, giving the train the green light to be launched. The first hydraulic launch coaster was Xcelerator reaching in 2.3 seconds. The world's tallest roller coaster, Kingda Ka at Six Flags Great Adventure, is capable of reaching in 3.5 seconds. The fastest roller coaster in the world, Formula Rossa, reaches in 4 seconds using the hydraulic method. Accelerator Coasters manufactured by Intamin commonly place a top hat element after the launch, which is a hill in the shape of a tower with a 90-degree ascent and 90-degree drop. Trains enter and exit this element in opposite directions. Top Thrill Dragster, built in 2003, includes this element followed by a brake run, while Kingda Ka, built in 2005, adds a airtime hill before the final brake run. Some hydraulic coaster layouts omit the top hat element altogether. Another manufacturer, Vekoma, began producing hydraulic-launched coasters in 2004 with the opening of Booster Bike at Toverland in the Netherlands, reaching speeds up to . Pneumatic (compressed air) Using the same type of system as a hydraulic launch, a pneumatic launch uses compressed air to launch the vehicle. The technology was developed by S&S as the Thrust Air 2000 model. The first coaster of this type was the Hypersonic XLC, opened at Kings Dominion in Doswell, Virginia, USA in 2001. This coaster closed in 2007. Another incarnation, the Ring Racer was open for only 4 days. Compressed air launches are able to provide more acceleration than traditional pneumatic launches, with Do-Dodonpa at Fuji-Q Highland in Japan holding the acceleration record since it opened as Dodonpa in 2001, launching passengers