Equally, what hasn't been considered is also the 'back office' stuff that doesn't get seen. Let's say we're a TOC who has catering and we've got two different fleets. Do fleet A and fleet B have the same combi ovens? If not, we need to do the risk assessments and operating instructions twice, potentially food cooking instructions too, one for each fleet. Each type of combi oven has different periodic maintenance requirements too, so the fleet teams have to write two sets of Vehicle Maintenance Instructions. We currently use a trolley to deliver the service, can the same one work on both fleets or do we need two separate designs of trolley? In any case, we'll need to ensure that the operating instructions for the trolley reflect how you do it on each fleet type, eg you have to park it in one place on one fleet but you can't park it in that place due to design of the other fleet.
One day the ops director of Speedy Trains decides that we're running fleet B down a route that fleet A have only ever run and says, 'Cuff, make it happen'. Fleet A you can dispatch from the back cab but fleet B, you can't, and at a number of locations on that route we've mandated that the conductor dispatches from the back cab. So I'd need to arrange PTI assessments for each of those locations to ensure that the conductors could safely dispatch the trains. Worst case scenario, I find out that they can't, so stop boards need moving for fleet B, but not fleet A. This might mean that the station dispatch staff need to do things differently too (eg positioning on the platform, use of CD/RA indicators), so they need to be briefed and trained on the differences between the two fleets. Meanwhile the planning team are scratching their heads and sharpening their train planning pencils, as only certain depots sign Fleet B so they need to ensure that the unit diagrams for fleet B tie up with the crew diagrams for the depots that sign them. The commercial teams will be asking things like, will the diagrams be interchangeable, and if so, do the seat numbers match up, otherwise we'll end up reserving seats that don't exist on one type of train.
Each fleet will need its own traction training course, so the person who's job it is to write the traction training for fleet A will now have to write and update another one for fleet B too.
A lot of what you'll see are the frontline things like training the drivers and conductors to work the different types of train, but there's a lot more 'management' stuff that goes into it as well, and a lot of it (like my example of the type of combi oven) isn't something you'd immediately consider.
