Locomotive placement

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Maybe the wrong place for this but what the heck...

I've noticed that the railroads are placing locomotives at both the front and back of trains. Like 2 or 3 in front and 1 or 2 at the back. Why is that? Before, they would just hook the locomotives all together up front.

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reconrider8

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I believe you are speaking of dpu's. They are there to support the head end locos in pulling and breaking as they are pulling longer and heavier trains now. From time to time you will see a set in the middle of a train. This is sometimes due to a crew shortage also so they just hook 2 trains together so it cuts at least 2 men out of work for that run.
 

W9BU

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Also, on long trains, it's sometimes helpful to have a locomotive on the rear of the train to provide additional brake pipe pressure to the train.

Some locals and road freights do switching with long back-up moves where having a locomotive on the rear of the train is helpful.
 

DJ11DLN

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DPU is becoming a fact of life with the "stupid long" trains they run these days, especially in the winter when it's difficult to hold brake pipe pressure. Also, the strength of couplers is finite, I think I read somewhere that a new one had a break rating of 450,000 pounds, which sounds like a lot, but figure that against the weight of a 15,000-ton train, and take into account that few of them are new, and you have a potential situation. Distributing the power helps to avoid break-aparts on these 130+ car trains.
 

franks_ham

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DPU lesson of the day:

DPU's are used in both mid and rear train applications for multiple reasons. Some of which have already been mentioned. The most IMPORTANT reason for DPU's is for HPT (Horsepower to Tonnage Ratio).

If you have 2 of the same engine rated at 6,000HP, all "online" (READ: RUNNING AND OPERATIONAL) and generating their full HP That's only 12,000HP. Now put 59 loads at a total tonnage of 4,461 behind it. Those two engines will run that train just fine...Take the same situation and put DOUBLE that tonnage behind it...What do you think is going to happen? Yup, YOU STALL OUT AT THE FIRST MAJOR HILL you have to cross.

The other reason for DPU's, especially MID-TRAIN, is to separate the LOADS and EMPTIES. General rule of thumb for RR Ops is to put all the loads DIRECTLY behind the lead units. Well if you have 8,922 Tons of LOAD behind you with 3 engines, and then about 3,000 Tons of empties behind that...You need DPU's between the two to help "PUSH" the loads and "PULL" the empties...In some circumstances you'll see DPU's on the rear of the empties as well to help push more.

For example, today's Manifest from Roseville, CA., to Roper, UT. will more than likely have a 3x2x2 setup. This means you will see 3 engines up front, 2 between the LOADS and EMPTIES and 2 on the rear. This is to have enough HPT (Horsepower to Tonnage Ratio) to climb Donner Pass. Most BNSF Transcon Intramodals (Chicago to Los Angeles, CA., Chicago to Seattle, WA., Chicago to Richmond, CA.) will have ALL their power up front as they are heavy but FAST PACED trains, meant to get from A-B in a reasonable time frame.

I hope this helps explain why you might see various configurations of power on trains.

Regards,

-Frank C.
 

N9JIG

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And to keep it on target for a radio list, they use freqs like 452.9125, 457.9125 452.950, 452.975, 457.950 and 457.975 for the data to and from the front and rear locomotives.
 

PJH

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Actually Frank, your on the right path but your mostly incorrect in the details.

There are several reasons why DP's or DPU's (Distributive Power, Distributive Power Units depending on the concept being used) are placed in a train.

First, it depends on the railroad. The UP and BNSF are heavy users of the technology, with NS and CSX now ordering units with the equipment and trying to get it to work on some of its more challenging locations.

Depending on the railroad and its goals, its mostly to run longer and heavier freight with less crews (why run two 6500 ton trains when you can run one long 12000 ton train?) Its simple economics. More you move with less, the cheaper it is to accomplish this. Not that this always works when you run into problems, and time lost fixing some problems may negate any cost savings. But that's another topic.

Although some trains may have empties behind the DP's when used in a mid train configuration, that's 99% not the case. You can have loads and empties in between the DP's. Its placement of the loads/empties as well as the type of car (if loaded or empty) is determined by railroad rules (known as "Car Placement and Train Make-Up Restrictions".

A weight profile of such a train may be (X for load, "x for empties):
Eng Eng XXXXXXXXXXXXxxxxxxxxxxxXXXXXXXXX Eng XXXxxxxxxxxxXXXXXXXXXX (EOT)

Also the type of grades being encountered may also restrict how the train is made up. Coming into or out of mountain or heavy grades will usually have the train pick up or drop off power after that segment.

It is also determined by the DP(s) power rating. Too much power can jackknife empties or long cars/short cars under certain conditions. There are all sorts of formula's used to determine proper placement. In any case, It cannot be more than 8500ft from the head consist. Any other remote consists behind that one cannot be more than 6000ft from it. This is due to the data radios being used.

If the train just has a rear DP(s), the length is still 8500ft.

Air is important (obviously) but mid train DP's on long trains are still a pain in the *** as the air has to pump to the rear of the train as well as towards the head end (and the head end is still pumping towards the DP's). This means your air will recharge quicker on the front half but may still take quite a bit of time to fully build behind the mid train units. Weather is also a factor. Colder it is, harder to pump the air.

DP's are also mainly used (especially on manifest trains and autoracks) to help keep train forces in check (drawbar/coupler ratings). Too much tonnage or power can break a knuckle (not horrible) or yank out a drawbar (very bad).

Another point, essentially there are no 6000hp units in opeartion. The use of HPT (horsepower per trailing ton) has also been set aside by a few railroads. HPT is not a true measure of what a locomotive can pull. UP has pioneered the concept of TPA or Tons per Powered Axle. Especially with AC units, horsepower does not directly relate to what a locomotive can pull.

You will not see more than two units on a rear of a DP train online due to power limitations (jack knife). If you see three, its usually due to one breaking down and they just tacked another unit on out of convenience. Per rules, its suppose to be setout at the next facility that can repair that engine.

For example, the SD9043MAC uses a 4300HP engine. The SD70ACe also uses the 4300HP engine. However due to electrical gear and other features, the 9043 is only rated at 116,000lbs of effort where as the 70ACe is at 120,000 (the new SD70ACT4 uses a 4600HP engine but power output is still 120,000).

Same goes with GE - The AC4400 is rated at 4390HP, the ES44AC/ET44AC at 4365HP yet they are rated at 121,000lbs. GE has been able to reduce cylinders, improve the electrical gear and keep the tractive effort the same. The BNSF ES44C4's are 4400HP motors are only rated at 105,000lb effort. The 4400HP engine in the Dash-9 results in 115,000lbs.

So, not all horsepower is created equal. There is a mathematical relationship between the two, but HPT is slowly falling out of favor, but still used.

Now, taking Franks example of 8000 tons and two 6000hp units, it will still work. You won't be doing 70mph but with AC traction, its done everyday. Even with two DC SD70's, its a 1.0HPT train and will take .8% grades at 16mph or so. On level or light grades it will make decent time.

DPU's are unmanned and controlled by the lead locomotive. The engineer can run the train for the remote units to follow throttle and dynamic brake commands at the same time as the lead, or can what is called "fence" the remote units to do something different. This is common in undulating grade where the train may be at different elevations at the same time so using this fence will help reduce in train forces.

Now, often on the east coast and some metro/industrial areas, some locals will have a locomotive on the rear. The locomotive is just along for the ride and not in a DP configuration, its there to avoid having to run around the train if it needs to change direction. Its basically there for convenience. Switching in many highly industrialized areas have very little track capacity to turn locomotive power or run around the train.

Distributive power technology has been around since the 1970's, but only recently refined. SP and Southern Railroad used Locotrol (Harris) with varied levels of success. BN tried it out as well and had all sorts of issues like the rest. It went from dials, to desktop boxes and now is integrated into the locomotive control screens. The original radio and control equipment required extended noses to house it (known as Snoot noses).

A good video on the old/original style equipment can be found on this NS training video:
https://www.youtube.com/watch?v=9IABM8UPplY
 

PJH

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Screen on the right is a typical DPU control screen. It will show the linked road numbers, power setting, air pressure, tractive effort and other general data and commands available.
 

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N9JIG

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I read someplace (Trains Mag maybe?) that while most of the CSX AC6000CW (or CW60AH) units have been retired or rebuilt with 4300 or so HP prime movers some of the later ones are still running with 6000 HP prime movers. It has been a few months or more since I read that so they too may have been rebuilt, re-engined or retired since then.

As far as DPU's go do any of the roads usually run many trains with mid-train AND rear end units?

Would mid-train repeaters be practical to allow longer train lengths? I imagine that latency might be an issue with this.

There was a story out there from decades ago about a Southern radio-link train derailing a couple cars and recoupling due to a lost signal from the head end, the lost cars were found after the train arrived and they were missing. I don't know if it was true or not but made for a good story nonetheless.
 

PJH

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Repeaters are used for lengths for EOT. You don't want longer trains due to in train forces and it's not practical trying to yard a three mile long train.

Any separation would break the train line and cause the train to go into emergency.

The only way possible would be that an angle **** was turned and once they go out of range for a certai time (no data heard) they go to idle.

Basically, it would have to be an overt act.
 

PJH

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CSX did/does have a few 6000hp units but very much in the minority. Some were rebuilt with standard FDL engines.

There are some intermodal and manifest trains that are running with three sets of power. It's not common and usually on long distance trains.

It all depends on where the train is going and the train makeup.
 
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I appreciate the info. guys. This is interesting stuff & certainly more complex then I thought.
 

byndhlptom

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DP Locomotives

For some enjoyable reading on Road Engine operation, search "tales from the Krug". Stories (w/ pics) from a now retired BN engineer operation out of Wyoming/Dakota's. Also has several interesting articles on engine operation, brake systems, etc.

Great writing style, you will enjoy

$.02
 

PJH

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Al worked Sheridan WY into Montana
 

Kitn1mcc

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Up here in New England on the smaller freight you will see this so they have a loco on the other end to make switching moves. (just like conrail used to some times haul around a Switcher) P&W do this all the time.

Also some times when a cab car dies they will throw a loco on
 

franks_ham

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Up here in New England on the smaller freight you will see this so they have a loco on the other end to make switching moves. (just like conrail used to some times haul around a Switcher) P&W do this all the time.

Also some times when a cab car dies they will throw a loco on
A cabcar wouldn't die as it's just that, A CAB in a CAR. The power on the other end of the train is what would've "died".

Regards,

-Frank C.
 
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