WARNING: Be very, VERY careful when watching this video. Once my Scarab makes it past the skybox, the screen begins flickering in a pattern that definitely can cause nausea, and even worse, legitimate seizures. I am not liable for anything that may occur to those who view this video.
So, with that out of the way...
The map shown here is a version of Assembly that I modded to include vehicles such as the Scarab, Pelican, and Banshee (the former, funnily enough, is the only one usable right now).
Seeing as how Bungie never really got around to finishing Scarab for the player's use, physical boundaries do not prevent you from doing as you wish. ;)
Oh, almost forgot...
Yes, I'm using the Steam version of the Master Chief Collection. But just to let you know, 343 Industries is updating this regularly, and the currently accepted methods of modding won't always work...unless 343i decides to release yet another modding kit. :P