The owner of the railroad (I forget which) that provides the cars was friends with the AD. The track belongs to different railroad company. They do cooperate, though..
I assume the AD Barta? It started about the same time he came aboard (hah.....see what I did there?)
Whoever the AD was helped cook up the idea with the railroad owner. It was more or less a one time and/or limited deal. But, turned out so popular that the owner of the railroad and cars decided to keep it going on goodwill. It's not his track, so if he pays Iowa Interstate who owns the track, he doesn't pay much. Either way, with all volunteers operating the thing, it's still a huge net loss for the railroad. The cost of managing all the moving parts is probably worse. Railroads have a lot of regulatory/insurance/headaches that are always lurking behind every corner. The University/Athletic department never contributed in any way.
There was talk at one point of bringing the steam engine owned by company that owns the track to run the Express once for a special event......back when it was running. Lay on to the whistle for the Wave.
Of course, I told someone who was involved, that was acceptable. Just no whistle for touchdowns, etc. Y'all know how I feel about artificial noisemakers like tornado sirens and such.