Loco-hauled metros?

[Nasadowsk]

There's a few deliberate power car-trailer sets running around too. The South Shore comes to mind, and doesn't Metro-North have some as well? Not quite the same thing, but it has similarities.

Most European EMUs are motor-trailer sets, though sometimes they'll distribute the equipment between a few cars.

[DutchRailnut]

Now if you're looking for a de facto locomotive hauled metro, there's the Broad Street Subway of the mid-1970s to early 1980s. the reason I've mentioned de facto is that a 5-6 car consist, 5 cars are hauled dead while the (barely) running car served as the locomotive. Those cars were literally falling apart, and somehow managed to cope with the 1980 World Champion Phillies crowd. Those were the days.

There's a few deliberate power car-trailer sets running around too. The South Shore comes to mind, and doesn't Metro-North have some as well? Not quite the same thing, but it has similarities.

not yet but the unpowered M-8 trailers are coming soon

[Patrick Boylan]

The Lackawanna old electrics ran motor-trailer sets, I think it was 1 motor for each trailer.
Aren't most NJT arrows and SEPTA Silverliners married pairs where one car doesn't have some equipment, like compressor on only one of each 2 cars? I thought I saw only 1 pantograph per sets of 2 cars.

But these are heavy railroad cases. The thread title's "metros", which I think applies only to subways and elevateds, not regular railroad, which usually has bigger equipment.

[MattW]

The Lackawanna old electrics ran motor-trailer sets, I think it was 1 motor for each trailer.
Aren't most NJT arrows and SEPTA Silverliners married pairs where one car doesn't have some equipment, like compressor on only one of each 2 cars? I thought I saw only 1 pantograph per sets of 2 cars.

But these are heavy railroad cases. The thread title's "metros", which I think applies only to subways and elevateds, not regular railroad, which usually has bigger equipment.

I did aim this at metros (light rail can count too) which at least in this country are exclusively EMUs whereas commuter rail operations are a mix. It seems that the most major drawback so far is the extra space taken up by a dedicated locomotive.

[Patrick Boylan]

Folks, please conserve electrons and quote only when you need to.

If you're going to include light rail, then in my lifetime I've seen photos or films that mentioned European streetcar motor-trailers.
I also think I remember Time of the Trolley and Trolleycar Treasury books mentioned and 1800's vintage locomotive hauled US streetcars, which indicates to me that professionals tried locomotives and decided it was better to go with mu's.
Extra space from locomotive is one drawback, I'm not sure I'd put it at "most major", which would get me a ruler whack from my grade school grammar nun, superlative 3 or more comparative 2.

Other reasons for mu's that change in importance along the spectrum from streetcars to railroads:
flexibility
fast acceleration
horsepower
size
articulated cars, which one might consider variation on motor-trailer. For example 3 sections, middle section suspended with no, or nonpowered, truck is not much different from 2 motor cars and a trailer. Or powered truck in the center with 2 non-powered trucks at the end, like NJT's Riverline, and I believe Austin Tx and most other recent diesel MU operations, is not much different from a locomotive between 2 cab cars.

[amtrakowitz]

This is more of a devil's advocate "why not" question, but would it make sense to run some metro lines (CTA L, LA Subway, MARTA, etc.) using [electric] locomotive-hauled trainsets instead of EMUs? Right off, I can think of two points against this: bad acceleration, and excessive current draw.

How about missing the third rail in gaps, thus requiring overhead third rail to bridge the gaps? This is not done with push-pull either, AFAICR.

Acceleration would not be affected depending on how light the trains are and depending on how powerful your motor is. You'd have more damage to the track due to the necessary adhesive weight for the motor, however.

New York's elevated railroads, when powered by steam, weren't slouches, even compared to the electrified version. And of course, the London Underground started its operations with steam power.

[ExCon90]

True, but when New York and London (and Chicago) electrified, they chose EMU.

[cristinarosales]

Locomotives are capable of achieving as much as 450 miles per gallon of fuel. It would be a reasonable idea to do this. I can't imagine that they wouldn't be capable of making adjustments for the acceleration problem. Even if it did require more electricity, the cost of using electricity would have to be significantly less than that of any fuel costs. The biggest reason I can think that it wouldn't make sense is simple. Locos are designed to pull thousands of tons of weight. That just isn't necessary for any type of commuter train in the world today. I am not sure why they chose EMU but that is the direction most went.

[ExCon90]

A compelling reason for not using locomotives was posted above by MattW: a locomotive takes up platform space, which is at a premium on many metros. For various reasons it is not always possible to stop with the locomotive beyond the end of the platform.

[Disney Guy]

Now if you're looking for a de facto locomotive hauled metro, there's the Broad Street Subway of the mid-1970s to early 1980s. the reason I've mentioned de facto is that a 5-6 car consist, 5 cars are hauled dead while the (barely) running car served as the locomotive. Those cars were literally falling apart, and somehow managed to cope with the 1980 World Champion Phillies crowd. Those were the days.

Do you think they removed the motors from the dead cars?

I would have thought that spinning the motor armatures of the dead cars would have consumed some of the horsepower of the one live car.

... articulated cars, which one might consider variation on motor-trailer. For example 3 sections, middle section suspended with no, or nonpowered, truck is not much different from 2 motor cars and a trailer. Or powered truck in the center with 2 non-powered trucks at the end, like NJT's Riverline, and I believe Austin Tx and most other recent diesel MU operations, is not much different from a locomotive between 2 cab cars.

I prefer to think of a trailer as a non-powered unit that is easily detachable and set aside when not needed, i.e. after the rush hour. And a locomotive as a unit which, although it is self propelled, is not equipped to carry much if any payload standing alone.

[jogden]

Locomotives are capable of achieving as much as 450 miles per gallon of fuel.

Just to clarify, that is 450 ton miles per gallon, which is quite different. The average diesel locomotive barely gets one mile to the gallon when measure the same as an automobile. Ton miles per gallon is a measure of the distance a gallon of fuel can move a ton. This is an important statistic, but it can also convey a false fuel efficiency. If you load one ton of stuff on a locomotive, you won't get 450 miles per gallon, you'll get about one, maybe. Those numbers are determined generally by freight trains moving long distances with enormous loads. A 15,000 ton freight train with three locomotives probably gets a few gallons to the mile going down the tracks, but when you divide that by the number of tons on the train, you get that number around 450.

The thing to remember with that statistic is that it generally comes from freight trains. They are more efficient, since they carry more weight. You usually do not measure the load on a passenger train in tons (although you could), and even if you did, passenger trains are generally pretty light by comparison and overpowered. Passenger trains generally have a fairly high horsepower per ton number too, which gives them great acceleration, but kills fuel economy. Add in lots of stops and starts like on a commuter train or metro type operation, and fuel economy goes completely out the window.

Now all that said, realize I am talking about fuel economy for the railroad industry. While passenger trains aren't the most fuel efficient trains out there, they are still an order of magnitude ahead of everyone driving their car! In a large group of people, it is far more fuel efficient for everyone to be on one or two trains than to be driving. The least fuel efficient train is still more fuel efficient than the most fuel efficient highway vehicles, when you compare the tonnage or passenger load that can be moved for a given fuel quantity.

[electricron]

Now all that said, realize I am talking about fuel economy for the railroad industry. While passenger trains aren't the most fuel efficient trains out there, they are still an order of magnitude ahead of everyone driving their car! In a large group of people, it is far more fuel efficient for everyone to be on one or two trains than to be driving. The least fuel efficient train is still more fuel efficient than the most fuel efficient highway vehicles, when you compare the tonnage or passenger load that can be moved for a given fuel quantity.

What you're suggesting is correct only if there are sufficient passengers on that train. If there's only one passenger with the engineer you'll be wrong. I have no idea where that break even poin is, but there is one.