Turntables? Those usually only get used when something (like an engine or motor unit) needs to be turned around. Many motor units that I see can operate just as well without turning around; some have cabins at both ends, or are in mated pair configurations with a "backwards" facing motor unit. Most carriages (that I see on a regular basis) have either half the seats facing one way, and half the other, or are reversible.

Regular switching track suffices to switch which end of a train a motor units runs on, and some smaller passenger trains can work fine in "push" instead of "pull" mode.