Train
Scheduling and dispatching

To prevent collisions or other accidents, trains are often scheduled, and almost always are under the control of train dispatchers. Historically, trains operated based on timetables; most trains (including nearly all passenger trains), continue to operate based on fixed schedules, though freight trains may instead run on an as-needed basis, or when enough freight cars are available to justify running a train.
keywords:letter_frequency, punctuation:no_comma