I've been riding Metro 3-4 days a week for the past 6 years, and I've only seen MTP on a train a couple times at most - and even then, it was just for getting from one station to another. Heck, it's probably single digits the number of times I've seen MTP in a station, let alone a train, and the majority of those times they were monitoring for fare jumpers at Rockville Station. You would think a station like Gallery Place would have at least one officer permanently stationed there.

Cops in NYC ride the trains. All the time.