as long as we seem to have a bunch of technical experts here, can I ask about these fancy tugs that I've seen at some airports? They have a sort of tuning fork shape if you look at them from above, and they surround the aircraft nose wheel with their arms and lift the whole front end up! Is there some advantage to this -- less stress or something? They must be quite expensive. At AMS for example where I saw one, the pushback doesn't use any other ground guys watching the wings either -- the tug operator just grabs the wheel and pushes. Maybe they have certainty that there won't be other vehicles out there.

Also, the UX gates at IAD on the other hand, go completely simple and cheap on the tugs -- it's like they're little more than electric-powered (it seems) style pallet pulling motors. I guess if it gets the job done!