I still maintain this is some developers idea of injecting some life into the airports. It happens too often to be mere coincidence, and I have been meaning to shoot some footage of this in action.
It seems like you can sit on the ramp as long as you like, and they’ll leave you alone. But as soon as you request taxi clearance, and start to move they seem to have this burning desire to get on to, or cross the taxiway you are on.
It probably depends on how big the airport is, but I have had one occasion, which I took a picture off to upload here somewhere, possibly even this very thread, where there were two buses, and some other vehicle holding short of the runway I was trying to get to. I just hope they set their mixture right.
At least on that occasion they seemed to be sticking to the ground vehicle path, which is very rare.