The latest advancement in
roller coaster design was first introduced to the public in the form of
X, which opened in late spring 2001 at
Six Flags Magic Mountain.
Designed by Arrow Dynamics, a once-thriving company whose production had dropped off in recent years, the prototype X marks the beginning of Arrow's comeback. The company designed an entirely new form of coaster, calling it the 4th Dimension, or 4D. Rumors about 4D circulated throughout the coaster community, but no one knew what it would be until someone found a video on Arrow's FTP server. The video was removed within a few hours of its discovery, but those who saw it told of an amazing new innovation.
On most roller coasters, the trains run parallel to the track. On X, they actually hang off either side, and the vehicles can spin independently, forwards or backwards in a 360-degree circle on a separate axis from the track. Even the track itself required a new design, with an extra rail to support the additional wheel assembly. As on an inverted coaster, the rider's legs dangle freely from the cars as they flip throughout the ride.
A ride on X begins with a twenty-story plummet toward the ground - which riders are sent through headfirst - at the near-vertical angle of 88 degrees for part of the 202-foot drop. The ride's top speed is 76mph, and there are six inversions along the 3,600-foot track.
Sources:
http://www.rcdb.com/installationdetail750.htm
http://americacoasters.com/NewFor2001/x.html
http://coasternet.danimation.com/x.html
http://www.coasterbuzz.com/features/trackspotting101/