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Note, this only worked properly with trains going in one direction.
If the triggering rail spanned both approaches to the crossing, wouldn't it work in both directions....assuming your layout is large enough to support a FULL train length on each side?
To your point, you do not want a situation where the Yellow and White wires are simultaneously triggered! I have dissected the electronics of the MTH crossing gate and it does not take kindly to such a proposition. ![:[](https://ogrforum.ogaugerr.com/static/images/graemlins/icon_frown.gif)
![mth 5-wire crossing gate without relay mth 5-wire crossing gate without relay](https://ogrforum.ogaugerr.com/fileSendAction/fcType/0/fcOid/153322190089827802/filePointer/153322190115129262/fodoid/153322190115129256/imageType/MEDIUM/inlineImage/true/mth%25205-wire%2520crossing%2520gate%2520without%2520relay.jpg)
Above diagram illustrates another "concept" in isolated-rail triggering. More than 1 isolated-sections can be tied together to create a single trigger wire to the gates. In this case there are 2 sections for the gates-down (yellow) trigger and 2 sections for the gates-up (white) trigger.
The MTH crossing gates are kind of a special case because it will flash the alternating red lights whenever the gates are away from the upper-most position. It will do this without a trigger on either input. So in addition to the FULL train length requirement between down and up trigger sections, the trigger sections must be long enough so a passing train triggers the gates to go all the way down or return all the way up. It only takes 2-3 seconds for the gates to change positions so this should not be a problem.
In both diagrams above just the 2 trigger wires (Yellow and White) are shown. The other 3 wires are connected per instructions.