How many locos does it take?

[Chaparral]

Just drove the Rogers Pass en route to and from the Kamloops Cowboy Festival and spotted some very long trains. One with three lead engines,two-could have been three but the guard rail cut the view-in the middle.

When there's a couple hundred hoppers, five locos, gravity and friction the horsepower required to drag that gross weight up and down the mountains is obviously enormous.

How do they decide how much HP is needed and where it's placed.

Oh yeah, how come the cars aren't pulled straight, off the rails in those very sharp uphill curves? The strain on the inside rail of a curve must be x to the umteenth power.

 

[lester perry]

beats me.
Les

 

[myltlpny]

Actually, that strain is just the sort of thing the railroads anticipate when deciding how much and where to put the motive power. Obviously, at some point the strain on the couplers would be exceeded with just the weight of the cars in the string. So typically on long runs, you'll see remote units midway and at the rear of the train to equalize the load. I'm sure there are more informed people on this list who can give you particulars.
Here in the Americas we just tend to stack up enough power to pull whatever it is we want to haul. This can be a problem when you can't see your entire train at any given time. Europe tends to build more powerful locos, using fewer to do the same job, but this is changing. Given the greater amount of goods to be hauled, at some point you start exceeding the physical capacity of the equipment.
Also, cars aren't pulled off the rails because they're being pulled by the car directly in front of it, not by the locomotive.

 

[lester perry]

Actually, that strain is just the sort of thing the railroads anticipate when deciding how much and where to put the motive power. Obviously, at some point the strain on the couplers would be exceeded with just the weight of the cars in the string. .

Before I start I know someone is thinking oh no more C&O. But that is what I do,sorry. I have read that in the last of the steam era the C&O used pushers behind coal trais being pulled by the mighty allegheny only when they start. because the couplers would fail under the stress. once it was rolling no problem.
Les

 

[Mountain Man]

Most I have ever seen was seven of the new "mega-diesels" (1.5 x the old ones?) on a coal drag over one-and-a-half miles long heading south towards Monument Pass.

 

[lester perry]

this I didn't see but I heard about, actually read about. more C&O, I believe it was 28, F7s A&B going through Ohio. pulling s short frieght. Now I have a question. Why would they do that?

 

[bigsteel]

this I didn't see but I heard about, actually read about. more C&O, I believe it was 28, F7s A&B going through Ohio. pulling s short frieght. Now I have a question. Why would they do that?

were they ALL running or were just a few,as those F7's may have been geeting worked on or scrapped.or thay could have just had a build up of F7's at one end of the line and needed to send em all back.--josh

 

[Ralph]

Seems likely to me, as Bigsteel said, they were moving the locos to another location where they were needed. Seeing 28 in a row would have been a sight to see!
Ralph

 

[lester perry]

You guys are correct. it was a power transfer. probably only one or two were running. I said two because of the dead weight of other locos. they were going from I think Toledo to Russell yard.
Les

 

[puddlejumper]

Well, I don't know the specifics and I'm sure some of the other more knowledgeable guys will chime in soon, but here is my take on things. The railroads are a little more advanced than you guys give them credit for. When I worked for CSXT we were all issued certain books and inside the Timetable for any particular division it included a Tonnage Rating Chart. This chart included each subdivision and a list of locomotives and ratings. For example (this is made up as I don't have a timetable handy)

Popes Creek Subdivision
Bowie-Brandywine
SD40, SD40-2, SD45, SD45-2, C30-7, C36-7 2200 tons
GP40, GP40-2, B30-7, B36-7 1800 tons

Brandywine-Pope
SD40, SD40-2, SD45, SD45-2, C30-7, C36-7 2000 tons
GP40, GP40-2, B30-7, B36-7 1550 tons

Pope-Brandywine
SD40, SD40-2, SD45, SD45-2, C30-7, C36-7 700 tons
GP40, GP40-2, B30-7, B36-7 450 tons

The above is not actual numbers and may be way off. All locomotives approved for use on that subdivision were listed. The was also a list of locomotives prohibited from moving over the division for various reasons such as clearances, axle loading, etc.

Now, you have your tonnage ratings for the locomotives, the paperwork has the tonnage for your train, so you know what power to assign. So, a 10,000 ton coal train going from Bowie-Pope needs 5 SD40-2 or a equivalent. Notice going into Pope has much higher ratings than coming back out of Pope, but the outbound train would be empty so the same power would be satisfactory.

Railroads also have a maximum number of powered axles. On CSX it was 24 on the Baltimore Division. It was later changed to allow 27 axles on the Popes Creek sub because we needed 3 SD80MACs for the pull up Duley's Hill. SD80MACs and other AC units are counted as more axles than they actually are because of the tremendious amount of tractive effort. 80MACs are 9 axles. 3 units = 27 axles online.

When you see 7, 8, 9, or more units in a train chances are only the first 3 or 4 are working. They do things a little different out west so I don't know. With a 24 powered axle limit that is only 4 SD40-2s, I know years ago the Popes Creek trains ran with 5 or 6 of them so things have changed some in recent years.

And as mentioned before the couplers rating can be exceeded if great attention isn't being paid to the tonnage of the train. We used to run 170 car coal trains from Brunswick to Baltimore with 3 up front and 2 shoving, 20,000 tons. Sometimes putting all the power up front is not the best option.

And one more thing the "Power Desk" is the group that decides what power to assign and also handles power balancing and shop transit moves. Usually they follow the numbers but sometimes they don't and when the engineer tells them he'll never make the ruling grade with the power he has and they tell him to just do what he's told. Usually this situation ends up with the train stalling, expensive delays and having to be shoved. Most engineers know very well the capabilites of the equipment on their division.

Dave

 

[Triplex]

SD80MACs and other AC units are counted as more axles than they actually are because of the tremendious amount of tractive effort. 80MACs are 9 axles. 3 units = 27 axles online.

CP counts AC-traction axles double. This seems an overstatement, since an AC4400CW doesn't have twice the tractive effort of an SD40-2.

 

[Russ Bellinis]

Sometimes in the mountains the railroad will put extra locomotives on the down grade, to get extra dynamic braking, especially if the helpers are needed back at the bottom of the grade. This is a common occurance in Cajon Pass where the West/South side of the pass is much steeper than the North end between Victorville and Barstow. They will use helper service to get the train up the pass from San Bernardino to summit and then cut them off. If they have a train going back down they will sometimes couple the engines on the tail end of the train if they are remote control units to get extra dynamic braking on the way down the pass.