Its based on the badge used by one of its predecessors the Great Northern:
The arms in my badge are the four main terminal stations on the NI rail network, Belfast, Bangor, Larne and Londonderry:
Heraldic crowns are common in railway heraldry, for example the rose,thistle and leek coronet used in the old British Railways badge:
Naval Crown, but for railways, that could be universal. My first idea was for a circlet with locomotive wheels. The "arches" of the crown would be the front figures of steam engines, with coloured headlights representing the precious stones that are often found in crowns, between which are two "Railroad Crossing" signs:
I posted this design on the flags forum for discussion, and Leonardo Piccioni had a pretty good idea:
Thus making the coronet look like this:
I also added the top of the locomotives 'smokebox' and some handles on the lamps for authenticity. however Leonardo didn't like the smokeboxes, so we came to the conclusion that the chimneys, lamps and wheels were the main feature and the inclusion of the smoke box would be down to the artists preference.
As seen above it could be used in the arms of rail companies, another example is the modified Irish Rail(IE) coat of arms design:
Or services itself such as the joint NIR/IE 'Enterprise' express between Dublin and Belfast:
However the Rail Coronet is not restricted to rail companies. It could also be used in civic heraldry. For example My Greater London coat of arms could use one instead of a mural coronet:
As London has four large train stations, as well as other suburban stations, and the worlds oldest underground rail subway system, or simply in the arms of towns or cities with a train station, like Belfast or my hometown:
These are just a few possible uses, but use of the heraldic rail coronet is really unlimited.