Self driving cars are a form of individual travel. An airport train is prescheduled and prerouted. The former beats the latter under specific circumstances only (or we would not have these two categories of transportation).

I would argue that traveling from and to a large airport is about as disadvantageous as it gets for individual travel: Your schedule is determined by someone else. Your route is already fixed. The only benefit of individual that I can think of in that case is the possibility to travel to/from somewhat remote locations directly from/to the airport.