See if this link works. If it does you'll see a BNSF car with "BUFFER SVC ONLY" stencil in the middle. Generally these cars are weighted with something like rock for ballast.
https://farm9.staticflickr.com/8647/16130249090_5b80a269aa.jpg
(BTW I was able to find the pic but couldn't get the page it's on to open for some reason, so I can't credit whoever posted the pic.)
And .... Tangent has recently offered a buffer car based on the 2-bay Air Slides (now listed as out of stock on their website but might be found at some dealers still. They have announced a brown BNSF version for 2016 so if you are a post BNSF modeler, you should be able to add one of those in the coming months.
Rio Grande. The Action Road - Focus 1977-1983
That's a buffer car, required by federal law as a safety measure between the locomotive and any car carrying volatile cargo. Keep an eye out for the "Ask MR" column in April's issue for a more detailed answer.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
Often I see tank car unit trains but with a different type car, usually a covered hopper, as the first and sometimes the last car. Does anyone know why this is done? I'm guessing either a weight issue or as a safety buffer. Btw thanks to all posters. I've been learning a ton.