Midway Engine?

Was out at Potter today and while trainspotting saw a rather large mixed freight going east with only 1 engine, but about halfway through spotted another engine about in the middle of the consist. And it sure sounded like it was under load pulling the rest of the long freight. Never saw this before, any ideas on what's happening, something new?
Not sure if anyone was in the cab, maybe remote controlled from the front engine??

called distributed power, the engine is repeating the actions of lead engine by radio link .

In addition, these units can be controlled in asynchronous mode from the lead unit (different throttle positions than the leader).

Ok with a midway engine or more on a consist what would be the limiting factor on the trains length? As it seems that with extra engines it could be endless, miles in length!!
But with any grade crossings that would be a downer for sure!!
I guess have to limit the length to the distance between 2 or 3 signal locations so the same train won't get a stop signal halfway through?

as soon as the lead unit passes a signal, the rest of the train gets a "stop" signal. it means nothing to the rest of the train, and has no bearing on operations. (unless the signal fails to drop, and displays a "false-proceed". the only signal that matters, is the one you're about to pass on the head-end.

trains are already "miles in length!", with absolutely no concerns given to grade crossings. the ability to clear a set of switches, to allow another train to pass, is the only real consideration in what limits train length, although with "psr", even this essential requirement is being thrown out the window.

Saw this configuration in action today near the Model Railroad Shop in Piscataway.
Single lead unit - green trash cars - single mid unit - tank cars
It was quite surprising!