I've seen it done with wyes and reversing loops..
There is a photo floating around here somewhere where Southern Pacific used a reversing loop to turn an entire train at one of its yards (near Tehachapi? I don't remember for sure)...
I've seen VIA Rail use a wye to turn its passenger locomotive around at some passenger stops in Ontario.. (It is necessary, because the AMD103/P42DC Genesis passenger locomotive is a full-width unit).
Here in New York City, I see Conrail (now CSX) freight trains coming onto Long Island via the Hell Gate Bridge arrive at the Fresh Pond Junction/Yard in Queens, and the locos are also turned around with a wye at the yard where it intersects with the Long Island Railroad's Montauk branch.
In Manhattan, the Metro North Commuter Railroad turns its trains around on a giant underground reverse loop in Grand Central Terminal. The MNCRR's predecessors (New York Central, New Haven, and Amtrak) all used the GCT loop.
Long Island Railroad, the other major commuter railroad here in the New York City area, avoids having to turn its locos completely, by using a DM30AC locomotive on one end of the bilevel commuter train, and the last bilevel car would be outfitted with a control cab (this arrangement is called "push-pull" I believe). And before the DM30ACs and Bilevels showed up, LIRR used a GP38-2 hood unit on one end and a de-motored Alco FA-turned-steam-generator/cab control unit on the other end. Freight trains on the LIRR would avoid turning the engines by using multiple units as previously mentioned by others.. Or they can use the wye at Fresh Pond and elsewhere.
Just what I see in my neck of the woods..
