S.D.O.

Well what does that mean you may be thinking well if you look at the shot you can see that the first coach behind the engine is off the platform this is where SDO comes in and it stands for Selective Door Opening where the guard can have certain coaches stay locked at shorter platforms to stop anyone falling out a door of a train when its not on a platform so this is my blip of a East Coast train at inverkeithing using the SDO proceedure