I have Lionel standard gauge trains. Both old and MTH.

[JP Wallace]

I would like to use some kind of automatic train control so  2 trains can run on the same track, so they don't collide.

[ADCX Rob]

Here is an automatic block control system that has been used by Lionel operators for over 70 years(click on diagram for full size view) and can serve as a model for what you want to do with your relays:

[JP Wallace]

thanks