yeah, this seems like a cool idea, and it doesnt seem too hard.
as far as i can see all you would need is:
-a GUI meter to measure the fuel.
-a script to slow down your vehicle when it is out of fuel.
-and some way to refuel your vehicle. the best thing i can think of is a flat plate that gradually refills your tank while youre on it. in the same manner that you convert the base pad things in team DM siege mode. as long as your vehicle is ontop of it, your meter goes up until its full!
:D sound good?