Here’s a quick one I’ve always wondered. Can a train running backward go as fast as one going forward? I’ve often seen a second or third engine in the middle or the end and can it running so I assume direction doesn’t matter?
Trains are typically pure electric (drawing power from overhead lines or a third rail), or they are diesel-electric, i.e. a diesel engine powers an alternator that produces electrical power which in turn is used to drive electric motors attached to the wheels. Unlike a car or truck that has several forward gear ratios and only one reverse gear ratio, going in reverse just requires switching the polarity of the electricity.
Japan’s N700S Shinkansen trains (and probably others as well) look exactly the same on the back end as they do at the front. When they reach the end of the line and need to travel in the other direction, they don’t turn the train around - they just switch which end has red lights and which end has headlights, and the cabin cleaning crew rotates all the passenger seats to face the other direction. That, and the operator walks from the cockpit at one end of the train to the cockpit at the other end.
Here’s a picture of two N700 trains stopped side by side at the same station. The one on the left will be going away from the camera when it departs (thus the red tail lights), and the one on the right will be going toward the camera (thus the bright white headlights).
It’s the same with city subways. Most lines end at a bumper and the motorman goes to the other end for the return run.
I do seem to remember a tight turn around loop somewhere in mid Manhattan though.
From this guy on Quora: Michael Sherrell, Urban Planner & Adjunct Professor - Urban Studies
“There are three major train loops within the NYC subway system. In a previous answer, the City Hall Loop for the #6 train to reverse direction from downtown service to uptown service. Currently the #1 train at South Ferry to reverse direction from downtown to uptown service while its replacement South Ferry terminal is under re-construction due to Hurricane Sandy. Both of these loops allow passengers to remain on board the train. The third loop in usage is for the #4 or #5 trains when those trains terminate at the Bowling Green (their last stop in Manhattan), where to return these trains to uptown service these trains travel on a parallel loop track at the #1 train’s South Ferry loop complex. Passengers however are not allowed to ride such #4 or #5 trains when they terminate at Bowling Green. From the #1 train platform at the South Ferry Loop platform one can easily see a waiting #4 or #5 ready to return to uptown service.”
While this is true of earlier diesel-electric locomotives, the modern design trend is to use alternating current instead of direct current. Among other advantages, this saves on the maintenance cost of replacing motor brushes. Alternating current motors cannot be reversed by switching the polarity. Nonetheless, it is still a trivial matter to run the alternating current motors in reverse.
(Am I being pedantic enough? If not, I have all day.)
For a more conventional train, loco at the front, load trailing after, it does matter. A train is like a length of chain. It is very hard to push a chain, as it will bunch up. Pulling stretches it out. A short train, or at low speeds, and it isn’t an issue. But eventually the compressive forces on a train will cause the individual cars to “ladder” slightly, where they twist about their vertical axis on the tracks relative to one another.
There is an intentional gap between the wheel flanges and the rails, this is needed to allow the slightly conical wheel surfaces to hunt for the correct point where inner and outer wheel (when going around a bend) that balances the different speeds whilst on a solid axle. Pushing a train will tend to force the ends of each car to one side or the other of the track, eventually as an alternating “ladder” of offsets. This force may limit the side to side hunting needed by the axles - meaning the wheels can’t find the required point to effect slip free rotation - so something wears - wheels, rails or both. The side force may mean it derails easier as well.
Fair point, I oversimplified. If you have a 3-phase AC motor being driven by a variable frequency drive unit, then you don’t “reverse the polarity” - you reverse the sequence of the three phases.
I heard diesel electric locomotives called “push me pull yous” because they were symmetric end to end, at least functionally if not exactly. This was in the 70’s when I repaired power management modules used on them.
There are some commuter trains that actually do this on purpose. It’s known as a “push/pull” arrangement. The Amtrak California Capitol Corridor train between Sacramento and San Jose is one such example. On the westbound trip from Sacramento to San Jose it runs the normal way with the locomotive at the front. For the return trip, rather than having to turn the train around or move the locomotive to the other end, they simply run the train in reverse, with the locomotive at the “back” of the train from the perspective of the direction the train is moving. The engineer has a second set of controls at what would be the front of the train on the eastbound trip, so the engineer is always at the front of the train whichever direction it’s going. And having ridden it in both directions I can attest that is does go just as fast either way (although I suspect it’s less aerodynamic in the eastbound direction, since it had the blunt end of a passenger car at the front rather than the sleek aerodynamic locomotive.)
Come to think of it freight locomotives can go either direction, too, although always at the front of the train. That is to say, it doesn’t matter which end of the locomotive is facing forward. I think pretty much all railroads run their locomotives “short hood forward” (cab closer to the front) nowadays, but many used to run “long hood forward”.
Example of a locomotive running long hood forward:
Metra (the Chicago-area commuter train service) does this on all of their routes where they use diesel-electric locomotives. The locomotive is positioned so that it is at the head of the train on outbound trips, and at the back of the train on inbound trips – each train has a “cab car” (a passenger car with a cockpit for the engineer at one end) so that the engineer can be at the front of the train in both operation modes.
This reduces turnaround times for the trains at the end points of their runs, as well as apparently reducing the amount of diesel exhaust that enters the main downtown stations, since the locomotives stop several hundred yards short of the passenger entry doors to the stations.
To the point that @Francis_Vaughan raises about pushing locomotives, these are short trains (usually five to ten cars), so the issues with pushing are less pronounced.
That’s a Norfolk Southern locomotive, and it’s interesting to note that the two railroads which eventually merged to form that line (Southern, and Norfolk and Western) were the lines which were noted for running “long hood forward.” This was apparently the results of an agreement which they had with the engineers’ unions, with the thinking that running with the long hood forward provided the engineer with additional protection in the event of a grade crossing collision.
Some trains have a conventional diesel electric freight-style road loco at one end and a passenger car with a control cab on the other end of a 3-5 car train. The pic at the far right of the the header in my link shows the old-style freight locos.
The other arrangement replaces the freight-style loco with a loco that matches the look of the rest of the passenger cars also with a control cab at the end. The pic at upper right in my link shows the matching loco end in the foreground and the second pic in the left column shows the other end, with the loco in trailing position.
In any case, they don’t turn the train around at either end of the line. The operator just moves to the cab at the other end and they depart going back the other way. They seem to run mostly loco forward inbound = southbound towards Miami and loco aft going outbound = northbound. All our stations are fully outdoors, so there’s no operational reason I can see for them preferring one way over the other. When I ride them, there’s no perceptible difference whether the loco is fore or aft.
It’s an interesting point that I’ve sometimes wondered about. The commuter trains in this area sometimes have locomotives at both ends, but more often they are single-ended, where there is only one locomotive and the opposite end of the train has a passenger car with a control cab at the front. These trains typically have somewhere around 15 cars or so, pulled in one direction and pushed in the other.
Anyway, I don’t recall any incidents here involving the “push” configuration or any concerns about its safety, but there was a British accident report on a major derailment years ago that blamed the push arrangement for making the derailment worse than it otherwise would have been. Still, they stopped short of recommending against it.
See the this LA train crash:
The Metro changed its policies after that crash. The front of the leading car is off-limits to passengers.
By “here” I meant where I am in southern Ontario. But anyway, that story parallels the British Polmont rail accident that I cited, whereby the push configuration was felt to have made the derailment worse, but the recommendations in both cases were measures to mitigate the possibility of derailment. The Glendale story is basically saying that in the absence of a locomotive at the forward end of a train, the front passenger car is more vulnerable to a collision, but it’s not about the alleged inherent instability of the push configuration.
The heavy haulage iron ore railways up in the north of Western Australia (there are 4 individual major railways) generally utilise multiple, identical locomotives. In support of the op’s question, there are two locos pulling from the front of the train but the second-in-line faces ‘backwards’. So they can certainly be connected to drive in reverse.
These trains also utilise additional locos for discrete sections of the track that are steeper. These are called bankers. These bankers come along and connect to the back of the train and push for the required section, then disconnect and head back to a staging point. These bankers can be facing forwards or backwards.
You can also have three locos in the front, in which case I’ve see the second and third both face backwards: