Why so much motive power for passenger trains?

[wjstix]

One other thing to consider is the diesel type. E units had two A-1-A trucks, the middle axle was unpowered. This helped maintain a smooth ride at high speed and distribute the engine's weight. When the GN streamlined the Empire Builder in the forties, it copied sister railroad CB&Q and ordered back to back E-unit sets to power the train. The 2000 HP E's did great on the flatlands of North Dakota, but had a hard time in the Rockies. With the unpowered middle axle, a lot of traction was lost when climbing. So they replaced the two E's with three (or four) 1500 HP F-units that had all 4 axles powered, and they were able to climb in the mountains and still maintain respectable speeds.

A couple of other things to remember is that the earliest F units were often purchased as A-B sets with a drawbar between the two units. FT's were designed to only work that way, GM had to make changes to create A or B units that had couplers at both ends when some railroads wanted that. So even if you really only needed 3 F units, you might have to use two A-B sets together. (A-B + B-A). Plus the eary diesels broke down a lot, railroads sometimes would assign 4 engines to a train that only needed 3 assuming one might break down along the way.

BTW I seem to remember reading that Amtrak used to figure one F40PH could handle 5 passenger cars, not because they couldn't pull more cars, but because more than five cars were too much electrical head-end power for one engine.

[JonathanS]

If you remember your high school physics you know that power requirements go up at the square of speed.  So to double your speed you need 4 times the horsepower, to triple your speed you need 9 times the horsepower.  To add another 45 mph on top of 90 you need 2.25 times the horsepower.

[jamnest]

During the passenger era the KCS would deadhead extra motive power in passenger trains.  It would not be uncommon to see extra GP and F units added on to the passenger E8s.

JIM

[Leon Silverman]

Therre is a topic in the "Trains" forum regarding train resistance.  Regardless of the posssibility that the constants utilized may be inaccurate,  the exponential increase in air resistance is typical.  A lot more power is required to tug 10 passenger cars at 100 mph than is needed to haul 130 frieght cars at ten or fifteen mph.  A typical econobox automobile can top out at around 90 mph, but you would need twice as much more horsepower just to increase that top speed another 45 mph (50%).

[Anonymous]

A few months ago, I rode the Canadian through the Rockys.  There were about 20 modern passenger cars and two locomotives.  One locomotive was to pull the train and the other provided electric power to the passenger cars.  On our particular trip, both locomotives broke down, causing a nine hour delay.  One locomotive was borrowed from CN, but they could not provide electricity to the passenger cars with just one.  Finally, we were able to meet a second locomotive and electric power to the passenger cars was restored.  Unfortately, we had one meal of KFC for 200 people from a small town of maybe 2000 instead of the very nice meals normally made in the diner's powerless kitchen.  I bet that was the biggest order that particular KFC ever had.  It was also somewhat chilly due to the lack of heat in the mountains.

That's funny. I took a dinner train trip several years ago with my wife and my brother and his wife. It was around the Madison area of WI and was to last a couple of hours. This was a little fan trip excursion behind an FP-7 with just a few cars. After a lousy, cold dinner, we had a drink in the lounge car and asked if we could go up into the engine and my brother and I got to go up to the cab. I remember intense heat and noise, walking up a narrow path to the cab for an exciting experience.

When we got to the cab, I happened to glance into the side mirror and noticed quite a lot of smoke from one of the cars. I asked the engineer if that was supposed to be happening and he nervously said "no" and said we'd have to leave the engine. They stopped the train for 20 minutes or so as I think they had to free a brake shoe. Quite a fan trip, maybe one of you was there as well.

Thanks for all of your comments.

Bill

[jimrice4449]

The power disparity also applies to frt trains.   A grain unit train and an intermodal train have widely differing speed requirements.  The intermodal train will generally get more power on the head end than the grain train in spite of the grain train being considerably heavier than intermodal.

[ericboone]

A few months ago, I rode the Canadian through the Rockys.  There were about 20 modern passenger cars and two locomotives.  One locomotive was to pull the train and the other provided electric power to the passenger cars.  On our particular trip, both locomotives broke down, causing a nine hour delay.  One locomotive was borrowed from CN, but they could not provide electricity to the passenger cars with just one.  Finally, we were able to meet a second locomotive and electric power to the passenger cars was restored.  Unfortately, we had one meal of KFC for 200 people from a small town of maybe 2000 instead of the very nice meals normally made in the diner's powerless kitchen.  I bet that was the biggest order that particular KFC ever had.  It was also somewhat chilly due to the lack of heat in the mountains.

[Philcal]

Two basic considerations exist for the use of multiple units in passenger service. Essentially, they are speed and reliability. Certainly, a single unit is often capable of pulling a passenger train, but speed can be limited, especially if the train is heavy. The use of additional units insures that the train can get over the railroad, and do it in timely fashion. Many other factors are present, but these are the basics.

[tomikawaTT]

Just to grab a number out of your original post and put it into perspective - 3 E-units.

The original EMD rating for a single E unit was 2,000 hp.  A 4-carbody FT or F3 set rated 6000hp.

A New York Central Niagara was rated at 6000 hp, with steam left over for train service (something the diesels had to have train heat boilers to supply.)

A Norfolk and Western Class J developed 6000 hp at the drawbar on an instrumented test run.  On another occasion, one reached 110MPH - a speed beyond the capability of the traction motors on diesels.

As for why the higher power to weight ratio of passenger versus freight trains, the entire reason was (and is) over the road speed.  A passenger expects to see the countryside outside the window moving past at a good clip.  A shipment of plumbing parts in a box car doesn't care if it's slogging along at a rollicking fifteen miles per hour.

Back in the day, one transatlantic steamship operator used the slogan, "Getting there is half the fun."  The people who really wanted to be on the far shore of the Atlantic voted, "Being there is ALL the fun," and filled all the aircraft several countries' air lines provided.  Transatlantic sea level passenger business is now as dead as the dodo, except for the cruise trade, where, 'Getting there is ALL the fun."

On the other hand, when it became possible to get from downtown Tokyo to downtown Osaka faster by rail than by plane, Japanese business travelers switched over and all but killed what had been the most profitable air route in Japan.  There's a lesson in this for Amtrak, if they care to think about it.

Chuck (who models everything Japanese EXCEPT the Shinkansen)

[ndbprr]

Tractive effort decreases with speed.  Use your car as an example.  Does it take less time to go from 0-10mph or 60-70mph.  When you get at the topof the torque curve you don't get much oomph for the effort.  Same with a fast moving passenger train. 

[TomDiehl]

A couple of reasons. As you stated above, one of them is speed, plus the ability to maintain that speed on grades. Having the whole power needs of the train with them kept them from having to wait for pushers (and the subsiquent banging in and out of the coupler slack).

They are heavier than an equivalent length of freight cars (at least for the era you're refering to). The older heavyweights were truly heavy. To provide a smoother ride, they actually made them heavier, some even had poured concrete floors.

Into the Amtrak era, they still need the locomotives for a different reason: head end power. The locomotive has a separate generator to provide power for use in the cars behind it.

Any trains with a "second" run (called a second section) were running full and the second (sometimes third and even fourth) section was the overflow. Remember, before WW2 most people travelled by rail and railroads would have a rush of passenger traffice at the same times of year that the airlines do today.

[Sperandeo]

Hello Bill,

Passenger trains were (and are) generally operated with a higher power-to-weight ratio than freight trains, both for higher top speeds and for quicker acceleration and recovery from slowdowns. Also, passenger locomotives were generally built to develop more of their horsepower at higher speeds – by using larger drivers on steam locomotives and lower gear ratios on diesels. This sacrificed some low-speed lugging ability in most cases, so some extra power – larger steam engines or more diesel units – would be needed to compensate when handling the heaviest passenger trains.

So long,

Andy

[Anonymous]

I have many books and postcards with pictures of passenger trains and have wondered why it took so much to pull them. I have a picture of a Great Northern O8 Mikado pulling 130 freight cars by itself. The O8 was probably the biggest and heaviest Mikado but still, that's alot of cars. Why then, did it require so much power to pull passenger trains?

I know that passenger trains usually traveled at higher speeds but they were often powered by 3, 4, or even 5 F units or 3 E units to pull 11 to maybe 15 cars. Were they really that heavy? My passenger consist book for the 1940's lists many trains either being pulled by a single Northern locomotive or the above mentioned F's or E's. It didn't seem to matter if they were Heavyweight or Lightweight cars (although, I'm sure it did make a difference).

If passenger cars are typically 85 feet long and freight cars were typically 40 or 50 feet long, you'd think that the locomotives that could pull 100 car freight train could pull 40 or 50 passenger cars. That being said, I know that there was not usually enough travelers to fill such a long train but there often was a "second" run with another set of motive power. Why so much power? Thanks,

Bill