That Steffen method looks much more theoretical than the other ones. The problem is you will have to line everyone perfectly at the boarding gate, and I believe

That Steffen method looks much more theoretical than the other ones. The problem is you will have to line everyone perfectly at the boarding gate, and I believe this is pretty much impossible (everyone wants to get in first, they're barely ok with letting other people go in front of them because even if it's faster on the whole, it's slower for that person, which is all that matters). The outside-in should be implementable, but people who travel together want to stay together, so it's going against them. Back-to-front still seems like the easiest method for an un-ordered, mildly-cooperative group of agents.