Electrical isolation of couplers

This is the original source. I had understood from context, that the “control rail” was the outside rail adjacent to the frog. I understand your point, but I had envisaged the “trigger” being an isolated outer rail, made live by the passage of train A and so, charging the outer rails under train B. It only needs to be live for long enough for train B to advance one rail length, after all. 

Seems like your last post is responding to a non-existent post but as I understand it, your application is the Automatic Control of Trains configuration per the classic Lionel "how to operate" manual from 1954.

@Rockershovel posted:

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So, as long as either the loco, and/or the leading car of any train running on this layout have a thumbtack or dumb coupler, I am good to go? 

Presumably by "dumb" coupler you mean one without a solenoid.  As I see it, it has nothing to do with whether the coupler is dumb or smart but rather if there is an electrical circuit whereby the stopped engine can receive outer-rail power from the coupler.  

That is, nothing says a locomotive or rolling stock's "solid" metal-constructed coupler (dumb or smart) must be electrically connected to the frame and outer wheels...whether or not this is standard practice notwithstanding.  Conversely, I am not aware of any O-gauge product which depends on a electrical circuit thru mechanical contact of coupler components as part of normal operation.

Separately, despite the elegance and simplicity of this method, is this really what you want...considering this is apparently a new setup?  I'm not suggesting expensive command-control or anything like that.  It's just that back in 1954 components like relays and diodes were few and far between to say the least!  Now these components are inexpensive and widely available and can enhance automatic train control setups.  Timed stops comes to mind.