Expanding on this idea of larger crowds and two groups. I had thought of something like that once if I ever did a passenger type of charter. If you have two groups and lets call them Group A and B. If 50-75 people get off the train each time its still a good number so the loading and unloading will be longer than say a group of 40-50. The idea of alternating groups is a good one. Say customer #1 gets group A, and Customer #2 gets group B. Folks could swap tags based on the locations and the customer preference. For example Customer #1 gets Mud Tunnel going west, and really wants to get Rock Tunnel also. He could swap his badge or whatever they use with someone else, and work it out that way, but still keep the number total the same on each runby.
Another idea I used a couple of times, was to sell a "Rider Only" pass. These people sometimes were friends or relatives who wanted to go along but were really not photographers. You don't sell these at the expensive of a full fare ticket, but if space is available this might be a consideration.
If folks are left on the train during photo runbys, they should be told to NOT BE VISIBLE, unless they are railroad-looking....brakeman, etc.
Depending on the destination for the day, one will have to figure out how many stops can be made. John Craft and I learned quickly in the early 90's that you can plan for a bunch of them, but reality says it takes longer than you think, and something always comes up to delay things. So for the sake of this discussion, if 10 runbys are planned each patron would get 5 runbys. Remember it takes a lot of time to get over the railroad and the crew times start well before departure time. Gettng larger numbers is doable, if the price is realistic and photographers understand its not going to be some of the prime locations where only 30-40 can fit. There is never a perfect scenario trip really, as there are infinite possibilities which makes it fun since the railroad offers a lot of options with 64 miles of mountain scenery.
Greg
PS Another option is for folks who do not have a pass for said runby, to be allowed on the dark side of the track as long as they are out of others shots. Of course it depends on the location. We had several "Rider Tickets" on a L&N 152 charter I did in 1988. Those fares helped to make me break even, which was basically all I wanted to do. Again this depends on space aboard the train.