Does RCT have an invisible "ceiling" above which you cannot build? I think it does, but I'm not sure. Recently, one of my friends who also has RCT was over at my house. We like to build very extreme roller coasters, and sometimes we make rides crash on purpose. Anyhow, he built a "Reverse Whoa Belly" coaster with a very long horizontal run and then a maxed-out tower. When we tested it, the car (as I expected) shot off the top of the tower. However, instead of shooting up, coming back down, and crashing on the top of the tower, it crashed on the way up, as if it had hit an invisible "ceiling".
On a related note, I've noticed when I build tower rides, I eventually get a "Too high!" error message. Is this the equivalent of the "Too high for supports!" error message?