Well, going one way, the left boundary is the outer one, going the other way round, it's the right one ... to complicate things even more this changes at a section like in FE Gold ... but for a simple check if a car is on the track, it shouldn't really matter because to be on the track you will ALWAYS be within one polygon (the outer, whichever that may be) and out of the other one (the inner). If you are out of both, you are always on the outside of the track, if you are inside both you are always on the inside ...