If a yardmaster was faced with a so-called lighttrain, one with just 60 cars, he might let it sit in the yard for another day until another 60 cars bound for the same location came in.
Unfortunately, few U.S. airports rarely offer the ease or public transport connections into their affiliated cities that Heathrow does, but one rare exception is Salt Lake City, a major Delta hub, which just this week debuted TRAX, a light rail train into downtown.