Locomotive arrangement & numbers

[storminorman]

With a day job that allows me view of a busy line I see plenty of rolling action. Two things that have intrigued me are why are locomotives arranged in a front, back, front...back position so often? Is there any special reason for this? And also what determines, if anything, the number of units on a train? I see anywhere from a single unit to as many as 9 sometimes.

 

[katyman]

If I undrstandwhat you mean by front,back, it is so that the lashup can go in either direction with the cab forward. Number of units usually determined by power required to move tonnage in the train.

Katyman

 

[storminorman]

Cab on the lead is always facing forward but not uncommon seeing others facing backwards.Explain the term 'lashup' please... I can understand the tonnage and it's relationship to units...never gave that a thought I guess..Tho I've seen 9 units on a very short train too.

 

[westbnsf]

The term "lashup" refers to the locomotives on the train. The number of units on a train is based on several things. Here are the major 2.

1. Like Katyman said it is based on the tonnage of the train. Depending on the steepness of whatever grades they have may dictate the number of locomotives necessary. For instance I have heard on the scanner before that a train needed .8 horsepower per ton. So lets say it was a loaded coal train with 16,000 tons. By the math (16000x.8) that means they would need 12,800 horsepower. Well if it had three C44-9Ws at 4,400 horsepower each, that would equal 13,200 horsepower so they would have enough.

2. Many times the number of units could be extra just in an effort to even out the number of engines. There will be extra locomotives somewhere and they may need to go to another yard or terminal that is short on locomotives. I suspect that may have been the case with your 9 units on a short train.

 

[JeffLH]

Cab on the lead is always facing forward but not uncommon seeing others facing backwards.Explain the term 'lashup' please... I can understand the tonnage and it's relationship to units...never gave that a thought I guess..Tho I've seen 9 units on a very short train too.

"Lash up" is a railfan term for an engine consist. Diesel electrics can run equally well in either direction. While usually it's desireable to have the lead engine facing forward, any others in the consist can face in either direction. Except in limited cases, the trailing units are just put together with no regard as to which way they are facing.

We have one requirement for trains going to a certain terminal to have at least one engine facing backwards in the consist. It's because the terminal can't easily turn power. That rearward facing engine doesn't have to be on the very end of the consist, just somewhere in the consist.

If you've seen 9 engines on one train, the railroad is probably moving power. Sometimes more power comes into a terminal than is needed for out going trains. They move the excess power to other points where it's needed. They may do this on a train or sometimes running what they call a light engine move. Extra engines may also have mechanical/electrical problems and are being moved to a repair point.

Many railroads today want only enough power needed to move the train actually working. Excess engines in a consist may be shut down or just idling on a short or light weight train. Those excess engines are just along for the ride.

Jeff

 

[katyman]

To JeffLH, I would say that trailing units are almost always put together with a regard to the way they are facing, especially on locals and yard duty. I can't remember when I saw a consist with the rear unit cab facing forward. True, interior units can and do face either direction. Places to turn power are usually few and far between.

Katyman

 

[JeffLH]

Just looking through all the great photography on this site, there's quite a few examples of the last trailing unit facing forward. Just as there's photos of the last engine facing backwards.

Locals and yard switching is different from through freight trains. There is a more compelling reason to have the power arranged in a certain way. A turn around local, if it's to be operated higher than 20mph over public crossings is going to need ditchlights on the leading end. If in cab signal territory, the leading engine is going to need to be equipped in most situations. Most cab signal engines aren't equipped to have them operate when running backwards, requiring the cab end to lead.

The yard at my home terminal is set up so that if you two engines MUed together, the preferred way is nose to nose. That way the engineer (no matter which end of the yard the engine is working) is on the side where the switchstands (and the switchmen) are.

Through trains on the other hand, are going from one yard to another. The power may stay the same on it's next assignment or just as likely be broken apart. Which way the trailing units face is usually of little concern. Most terminals can turn power if they need to. They just grab them as they need them to build the power block required.

Jeff

 

[storminorman]

Above answers all make perfect sense to me..Thanks guys!