The difference is, they have traffic controllers and the train have their own dedicated rails, almost no obstructions and a train into train crash danger situat

The difference is, they have traffic controllers and the train have their own dedicated rails, almost no obstructions and a train into train crash danger situation rarely arises. The planes have a lot of maneuvering space to all sides. Car traffic and streets are more dense and often have humans crossing them without regards to laws, bicycles, motorbikes, road construction and bad weather. Not saying one auto pilot system is better than the other, however, they operate in different environments.