Load 'Em Up

Technical question--I have been watching some Amtrak Videos on U-tube of the CZ. I have noticed that thay do not put many cars behind their locomotives comparitavely speaking. Does anyone know what Amtrak does as far as % of load they put their locomotives under? I may not be asking correctly, if for example one locomotive can handle 50,000 ton at 100% capacity and Amtrak loads their locomotive to 25,000 ton that would be 50% load of max capacity. I guess what I am asking is do they "De-rate" their engines to last longer?

The primary power issue in passenger train service is acceleration and maintaining speed on grades. If you would accept freight train accelerations and grades, which would result in much slower schedules, particularly on routes with multiple long grades, such as that of the Southwest Chief, then you could power a passenger train just like a freight train, and never need more than one unit per train.

Also generally the weight per axle on passenger units is less than that on freight units. At very low speeds the ability to move a train is determined by adhesion, wihc is directly related to the weight on powered axles.

To answer the original question: Amtrak does not de-rate their engines. They are using full power in acceleration and going up the grades.

It should also be noted that in addition to George's excellant points, that there are runs where Amtrak runs 2 locomotives simply because the host RR has told them that they cannot tolerate a failure in certain areas of the run. So running 2 helps gives insurance that the train will make it through.

Also don't forget that HEP draws off some of the power from the prime mover too. I seem to recall that a P42 which produces 4,200HP only has something like 3,800HP left for the traction motors if its providing HEP.

George Harris said:

Amtrak does not de-rate their engines. They are using full power in acceleration and going up the grades.

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In general, how severe is the acceleration "penalty" for adding a car? E.g., from 4 to 5 on the Carl Sandburg (1 engine) or 9 to 10 (on the CZ (2 engines)? Or put another way, would it affect OTP, assuming the more blatant pad elements were removed from schedules.

Would it be fair to say that the consists are as short as they are because either extra cars are not needed or not available, not that engines are operating at 100% of capacity.

George Harris said:

The primary power issue in passenger train service is acceleration and maintaining speed on grades. If you would accept freight train accelerations and grades, which would result in much slower schedules, particularly on routes with multiple long grades, such as that of the Southwest Chief, then you could power a passenger train just like a freight train, and never need more than one unit per train. Also generally the weight per axle on passenger units is less than that on freight units. At very low speeds the ability to move a train is determined by adhesion, wihc is directly related to the weight on powered axles. To answer the original question: Amtrak does not de-rate their engines. They are using full power in acceleration and going up the grades.

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When I was living along the route of the Southwest Chief Amtrak was still running F40PH's and I'm guessing the weight per axle of an F40PH is similar to (if not more than) the per-axle weight of the SD40-2 locomotives that were so common on freights. Not to mention that more axles generally translates to more traction despite a lower per-axle weight. It seems to me that we should be talking more about gearing and power-to-weight ratios more than weight per axle when talking about the requirements of passenger trains. And as Alan mentioned Amtrak's need to avoid fees and other penalties for breaking down on freight-owned tracks.

PaulM said:

George Harris said:

Amtrak does not de-rate their engines. They are using full power in acceleration and going up the grades.

Click to expand...

In general, how severe is the acceleration "penalty" for adding a car? E.g., from 4 to 5 on the Carl Sandburg (1 engine) or 9 to 10 (on the CZ (2 engines)? Or put another way, would it affect OTP, assuming the more blatant pad elements were removed from schedules.

Would it be fair to say that the consists are as short as they are because either extra cars are not needed or not available, not that engines are operating at 100% of capacity.

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I can't give you a detailed answer (because I don't know), but the answer is that it depends, in part, on the locomotive, and in part on exactly how many cars you're dealing with. Going from four cars to five wouldn't cause that much of a difference, but going from six to seven, or from seven to eight might cause a noticeable slowdown.

A single locomotive could pull nine or ten cars if it had to. One of today's Michigan trains had one engine pulling eight coaches and a cabbage (which weighs much more than a regular coach). It probably lost a little bit of time due to the slower acceleration.

The locomotive type makes a difference as well. An F59, for example, can get you from 0 to 45 pretty quickly, if your train is light enough, while a P42 will take a bit longer to get there. But to go from 60 to 79, the P42 probably has a slight advantage.

But to answer your question, consists are kept short due to either demand or equipment availability, not due to locomotive ability.

Thanks for all the good info. As I am new to the train world I have a craving for how things work. I was just noticing that in general Amtrak pulls the cars with a much less Locomotive to car ration than freight does. Now I know why. Thanks guys---

AlanB said:

It should also be noted that in addition to George's excellant points, that there are runs where Amtrak runs 2 locomotives simply because the host RR has told them that they cannot tolerate a failure in certain areas of the run. So running 2 helps gives insurance that the train will make it through.

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That didn't help on the SWC that I was waiting for. It rolled into Flagstaff around 4 hours late after both the Amtrak engines packed in so there was a freight engine on the front, which just lead to it getting even later. The rumour I heard on the train was there was something up with the diesel when the refilled in ABQ (it was on-time until then) but I never did find out if that was true or not.

Chris J. said:

AlanB said:

It should also be noted that in addition to George's excellant points, that there are runs where Amtrak runs 2 locomotives simply because the host RR has told them that they cannot tolerate a failure in certain areas of the run. So running 2 helps gives insurance that the train will make it through.

Click to expand...

That didn't help on the SWC that I was waiting for. It rolled into Flagstaff around 4 hours late after both the Amtrak engines packed in so there was a freight engine on the front, which just lead to it getting even later. The rumour I heard on the train was there was something up with the diesel when the refilled in ABQ (it was on-time until then) but I never did find out if that was true or not.

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Well the Chief isn't one of those trains that just has an extra engine for the safety factor. It needs both engines to get over the mountains. The Silver's on the other hand actually don't need two engines, but yet they get them due to CSX's insistence.

Chris J. said:

That didn't help on the SWC that I was waiting for. It rolled into Flagstaff around 4 hours late after both the Amtrak engines packed in so there was a freight engine on the front, which just lead to it getting even later. The rumour I heard on the train was there was something up with the diesel when the refilled in ABQ (it was on-time until then) but I never did find out if that was true or not.

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The freight locomotive has low speed gear which probably can't reach 79 mph. I don't know what's the top speed for the freight locomotive. Amtrak locomotive has high speed gear which can hit 100 mph.

Freight units are limited to 70 mph. That's why, when an Amtrak train has to be pulled by a freight unit, it is almost guaranteed to lose time.

Trogdor said:

Freight units are limited to 70 mph. That's why, when an Amtrak train has to be pulled by a freight unit, it is almost guaranteed to lose time.

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They also have a harder time getting up to speed due to gearing, no?

gswager said:

Amtrak locomotive has high speed gear which can hit 100 mph.

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110 MPH.

ALC_Rail_Writer said:

Trogdor said:

Freight units are limited to 70 mph. That's why, when an Amtrak train has to be pulled by a freight unit, it is almost guaranteed to lose time.

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They also have a harder time getting up to speed due to gearing, no?

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No, they'll actually probably accelerate better. Assuming everything else is equal (horsepower, traction, etc) varying the gearing is a tradeoff between acceleration and top speed - you can gear a locomotive to have a really high top speed, but it's going to take forever to get there. That's why cars have transmissions - you can use the low gears to get better acceleration and then higher gears for cruising on the highway.

Once again, I am learning how trains operate. On a run such as the California Zypher is there a time that the locomotives are under 100% power? That leads to another question. Can a locomotive run at 100% rated power indefinately, or do they have a duty cycle, so to speak?

piperdriver said:

Once again, I am learning how trains operate. On a run such as the California Zypher is there a time that the locomotives are under 100% power? That leads to another question. Can a locomotive run at 100% rated power indefinately, or do they have a duty cycle, so to speak?

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I would imagine that it's a bit more nuanced than that. I'm guessing the traction motors could run at maximum effort almost indefinitely while the diesel engines would not be able to run at maximum RPM continuously or you would drastically increase their maintenance schedules and shorten their lifespan considerably.

I am familiar with diesel engines. Most of them are quite content under load against the governor. I am trying to relate this to the aircraft field that I am in. The turbine engines have a max rated power, and a max continuous power rating. The max continuous is typically not signaficantly lower than the max power setting, but it is enough that it is the difference of the engine living or having a melt down. The traction motors were what i was mainly interested in. Also is Alternator/Generator (jump in and correct as to which one) was a question in my mind also.