I believe it is actually a hard problem but there is a good solution being explored on the UK. Read the rails like a card magstrip. Trains first traverse the

I believe it is actually a hard problem but there is a good solution being explored on the UK. Read the rails like a card magstrip. Trains first traverse the track scanning the entire length in detail with careful speed and location tracking. Then trains can subsequently pattern match to the rail for location and speed. The rails can also be coded with info like patterns although that's not generally needed. Trains get loaded with info about the track they'll be on and then can monitor progress themselves.