Tank car train ends

Remember, those are mostly unit trains, thus having the required "buffer car" on the rear as well as the front, eliminates the need for switching of the whole unit train set.

Actually, it has nothing to do with couplers.  All US automatic couplers on interchanged cars or locomotives will couple together -- standard couplers, tight lock couplers (passenger equipment), and shelf couplers (tank cars).

The reason for the buffer car is to provide the minimum separation (between certain cars placarded for certain hazardous materials and an engine, passenger car, or occupied caboose) required by Federal law.  If the tank train stalled and had to be shoved to clear the main track, or had to be switched from the rear, then a following train or locomotive crew (and the railroad) would be in violation of Federal laws if they coupled directly onto the rear tank car (providing, of course, that it had a hazardous material placard displayed).  Corn syrup and other non-hazardous materials carried in tank cars are exempt.  It's the cargo, not the type of car.

So, standard practice is to place a buffer car at the rear of a train in which the rear car is placarded for hazardous material, regardless of whether it is a boxcar or a tank car, and regardless of the type of automatic coupler it is equipped with.  It is not a requirement to do this, but the railroad is spinning the wheel of fortune and hoping to win, if it does not take this step, and the monumental amount of unnecessary delay involved in having an engine -- especially if it is leading a following train -- hunt down a buffer car, move at Restricted Speed with a Trainman hanging onto the side of the car on the leading end while shoving, possibly for miles, up to the hazardous car at the rear of the preceding train, etc., is obvious and is just plain bad operation of a business and subjects the employees to unnecessary risk of injury.

Proper Preparation Prevents Poor Performance.

I would guess the trains you saw with the buffer car on the rear were empty.

On loaded oil trains or trains with a hazmat loaded car near the head end, ALL available buffer cars have to be on the head end, up to five, between the locomotives  and the first hazmat loaded car. If only one buffer car was available, that was all that was needed, but if there was a buffer car on the rear of a train with no attached locomotive, it would have to be switched to the head end or just cut off and left behind which was the usual case.

As late as a year ago, the BNSF was delivering oil trains to the UP in St. Louis with a buffer car on the rear, we would have cut the rear buffer car off to comply with the rule, how the BNSF could do it I don' know.

I did talk to some FRA people and suggested that it is a good idea to leave a buffer car on the rear of loaded trains just in case they needed a shove or the train was required to change directions and would not have to switch the buffer car to the other end.  But I am not aware of any changes in the rule.

Dan

Thanks to all you for your answers!  So nice to get "real" answers from real RRers for us "know it all" armchair RRers