Preisely, Paul. Enter the pit road as if you were in a Grand-Am race, by following the full pit entry.
No cutting across the grass, and being sent back to the beginning of the pits.
Also, the second part of the rule is about pit exit, follow the proper Grand-Am pit exit. You'll see at around 0:11 seconds in the video below there are cones at the NASCAR pit exit that don't exist in GT5. You have to turn right and follow the road racing pit lane exit by the grass on drivers left and to the left of the pit exit wall that comes up at the end of the grass.
http://www.youtube.com/watch?v=zLESzTDdf6s
That is the track map, there is nothing remotely complicated about getting onto and off of pit road. enter pit road like they do in NASCAR or Grand-Am, exit pit road following the extended pit road exit.
Chris