In April 2013 we spent a week in San Antonio Texas, for our son's graduation from Air Force Basic Training. This is our trip diary from Day 3, our first day on base. See More Here:
As near as we could tell, ALL the roads in San Antonio are a loop. Which is nice, because if you miss your exit, no big deal, just take the next one..
When your airman has a town pass, the important loop to remember is the 1604, shown in red here. Your airman must remain INSIDE of this loop while on town pass. He can apply for exceptions beforehand, if you have family nearby, etc. This is a large loop, you should not have any trouble remaining inside of it.