I don't generally give a CL of five, but perhaps this deserved one...

You're obviously talking about the marshalling of freight trains. There are strict rules laid down as to what class of freight is marshalled where in a train - such as hazardous goods at the front (rear-end collisions were not exactly unknown in the past, when most of the regulations were drawn up!). I'm unfamiliar with today's rules on the sorting of goods; the only mandatory provision I definitely know applying to the last vehicle in a train is that it must carry an "end of train" marker. This "Zugschlusssignal" varies from one eailway to another; some use a red lamp, some a red metal disc or plate, others flashing red LEDs.

Just for interest's sake, take a look at some illustrations at the URL below.

per Google search of:
"what is the last car of a freight train called_"
Confidence level is same as for Wikipedia as a whole. - Caboose is (5) - Brake van of a goods train is (per Wiki)