I believe they're no longer used, but only because I haven't seen them myself during occasional observations of BNSF trains, nor have I seen them in photos or mentioned anyplace else.
They were used for 2 reasons, as I recall: 1) Saving time by not having to stop a mainline train to refuel during a run; and 2) Saving money by being able to buy diesel fuel at a cheaper location and then essentially move it as a "company service" move - but between the locomotives which are also consuming it as they go, instead of further back in the train.
A major reason for not using them may be the new on-the-main-line fueling station at Sandpoint, Idaho, and similar facilities elsewhere. Also, with mandatory brake and train inspections every 1,000 miles or so, that provides a good opportunity to refuel then as well, to avoid any other delays for that.
Likewise, cheaper diesel prices until recently may have obviated any significant savings from being realized. In the meantime, the railroads have gotten a lot more sophisticated about hedging their fuel costs, and scheduling and operating trains for better fuel economy.
Often overlooked are the petroleum products coming from the tar sands in western Canada. Obviously that's not far from BNSF's lines, and more importantly, it tends to be cheaper than from other sources. That's because there's not a huge local demand, nor a pipeline or other cheap and large capacity transportation to export those products out of the US MidWest region to places with higher demand, so there tends to be a relative 'glut' of over-supply and hence cheaper prices in that region, of which BNSF can take advantage. I don't know what or where the 'benchmark' crude price is up there, but I understand that a comparison of the commodity prices for West Texas Intermediate crude at the common transfer point of Cushing, Oklahoma with that of the Brent North Sea (UK) crude reveals a significant spread, which didn't used to occur. See, for example:
http://knowledgeproblem.com/2011/02/24/more-on-cushing-and-the-wti-brent-crude-oil-price-spread/
http://www.econbrowser.com/archives/2011/02/brentwti_spread.html
http://ourfiniteworld.com/2011/02/19/why-are-wti-and-brent-prices-so-different/
Also, the bigger tanks and better fuel economy of the modern units may have reduced the consumption per mile and hence increased the range a wee bit.
- Paul North.
Haven't seen one in use in ages (that could, however, be due to my geographic location--BNSF's a mighty big railroad!). I think I did see one at Rochelle once, renumbered into the normal tank car series, being treated as just another fuel-supply tank car.
Carl
Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)
CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)
Still being run or has BNSF stopped using them in engine sets?
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