Doh! Looking at the map, the address I stated still seems right (30700 W Patton Rd), but you're right that it's not APG. I just googled that address + arizona, and a bunch of "Toyota Arizona Proving Ground" and "Toyota Technical Center" links came up.
I'm guessing it's Toyota's
but it would be cool if you can see!
It looks like you could take Grand Ave to Patton Rd. Take Patton west all the way over to 307th Ave. Go north to Peak View Rd. Then go west on Peak View and it looks like it turns into the facilities entrance.
edit: found this too...
Quote:
Taisei Corporation, Japan�s largest construction firm, completed the Toyota Proving Ground test track in Arizona in 1993
