If you visit my web page (http://capital2.capital.edu/admin-staff/dalthoff ) you will find a link to a collection of amusement ride patents. At the bottom of the patents page, after the descriptions of the Runaway Train and Space Shot patents, there is a table of links to patents on the IBM Patent Server. One of those patents is for "Amusement device in the form of a roller coaster, monorail, or the like." That patent explains the magnetic/mechanical anti-rollback system used on Superman:Ride of Steel, which may also be employed on Millennium Force.
It's the last patent on the list. A direct link to the patents page is http://capital2.capital.edu/admin-staff/dalthoff/patents.html
--Dave Althoff, Jr.
(fixed formatting)
*** This post was edited by RideMan on 1/22/00. ***