Yes there are 3 different bus line through the Fort. Purple, Yellow, and Orange. The good thing for the OP is that although they run through different parts of the Fort, they all start and end at the same points.
The OP can drive to the Fort entrance off Vista Blvd, give your name to the guard for your ADR, he'll tell you to park and walk to the Outpost Bus Depot which is on the far side of the main parking lot. Take the first PYO bus that comes along and ride it down to the Settlement Bus Depot which is down where Trails End, the lake and boat docks, and Hoop Dee Doo Review are. Get off and walk down toward the lake and the TE checkin podium will be outside the building on your left.
Just do it all in reverse to get back to your car.
Enjoy it!
Bama Ed