After looking at old airports and stuff on Google Maps and on a few websites on the subject, I was browsing around Davis-Monthan Air Force Base in Tucson, Arizona and I noticed a road that happens to have a gate, with
the gate wide open. The road leads on to the runway and tarmac areas from the northern end.
To get to this gate, you have to get into the air force base first, as the gate is inside the base boundaries, so its not exactly going to be easy to sneak into the base's runways and tarmac, but if this gate is always open, it wouldn't be hard to reach once you get onto the base.
-- John O.