I have noticed a lot of trains passing through this flat part of the country (Streator, IL) on the BNSF have locomotives on the rear. What is the purpose of these rear units? They are running because you can see the exhaust. Are they helping push these extremely long stack trains or are they just being moved?
They are “distributed power” - Analogous to a pusher in function, but unmanned and controlled via radio from the lead locomotive. Sometimes you can find them in the middle of the train, too.
There are specific rules for moving a ‘dead’ locomotive (ie, one that isn’t contributing power to the train). I don’t recall that those rules allow said locomotive to be at the far end. If a railroad is moving motive power around, it’ll likely be together with the head end power, but not cut in for locomotion purposes (the brakes still have to work).
As flat as Illinois looks, there are still some grades to contend with. It’s entirely possible that while where you are is flat, the train has either already faced a substantial grade, or has one coming up.
These units are Distributed Power Units (DPU). Basically the idea is that when you reach certain strain on the coupler from the power of the locomotives, the couplers will break. Removing the concentration of power at the head end helps spread the coupler strain and power across the entire train, preventing the couplers from breaking.
With the engineer controlling the locomotives at both ends, he can get better train dynamics (for example, if the train is cresting the grade, the rear units can still be powered while the lead units are not). And when it comes to braking the train, the brake application can be initiated from both ends of the train, theoretically allowing the brakes to apply twice as fast. This allows longer trains to be operated safely.
So, does the engineer have a seperate control for the DPU? Sohe would have two sets of controls…Or is the DPU control “slaved” to the throttle/reverse/dynamic brake controls, so it mimics the head end power?
Hi Iam a engineer and to operate the dp I can do with the rear dp unit is split the screen and move to back with the power and dynamic brake. I have operated several dp trains and they seam to handle better for example on a 15,000 ton grain train I will set it up with 2 units on the head end and 1 unit on the rear that is most often 3 ge dash 9s that is 13,200 hp that figures to .8 hp per ton. I can get the train to prescribed speed faster in dp than with all 3 units on the head end.
Rodney
Mostly they are being used as help power, because there might be some hills, where they going, or where they came from. Helper engines can also be used to slow trains, going down hill.
Many of these stack trains are heavy with grain , as many of the trains leaving LPCHI get rear power since most of the trains are loaded with grain for China .
One nice things about DPU is when starting on any substantial hill you can start the DPU before releasing the air brake to keep the rear end from rolling out. Slack running out when starting has been known to break a knuckle.
There are some places I will avoid stopping with 0.5 hp/ton unless the train is a DPU. Having an engine on the back makes it a lot easier starting out. Less chance of ripping the train up if the lead units momentarily slip.
Jeff
Back in steam days the Santa Fe’s Edelstein Hill was a helper district where the helper would typically cut of on the fly, and there were many other places in “flat” Ill. with stiff grades, generally comming out of river valleys.
the 1 or 2 engines at end of trains thru streator il, are for the big hill at EDELSTEIN,ILL.