Don W,
Those race conditions are why something other than the signals had to
control who was supposed to move first. Some signal systems got in to
interesting ideas like biasing the two directions or something I recall
called 'double approach' but I don't recall the details well enough to say.
They were part of APB which tried to improve the safety over long single
tracks. APB uses a waterfall from one end to the other of the single track
so the distant signal would show stop to the opposing direction. There are
still races possible as I understand it, but I'm not sure how they handled
it. These were more popular in the US west which had many miles between
passing points and the dispatcher usually had a couple trains going one way
before opposing traffic would try coming the other way.
It all comes back to why the railroads used signals only for safety of not
running into another train. Only in CTC, where they were controlled to not
show the clear, until the dispatcher had decided who was supposed to move
first. Everyone else waited at the control point until the dispatcher
decided otherwise.
Can you automate some of the dispatching, yes but it isn't the simplest way
to do things. But for models, I've found way too many people 'fear being the
dispatcher'. I even did a clinic in 2014 with that as the subtitle.
-Ken Cameron, Member JMRI Dev Team
www.jmri.org
www.fingerlakeslivesteamers.org
www.cnymod.org
www.syracusemodelrr.org
Ken Cameron