Thread Tools Display Modes
Old 02-23-2017, 01:57 PM
MaxTheVool MaxTheVool is offline
Join Date: Aug 2000
Location: Santa Clara, CA
Posts: 11,642
Weird visualization paradox - width of trains

(Not sure if GQ is right for this...)

So here's a kind of mental optical illusion that's been bugging me for years...

Imagine the interior of a commuter train car. There's an aisle wide enough for people to walk down. And on each side is a seat, usually wide enough for three people to sit on. Visualize how wide that needs to be.

Now visualize how wide the distance is between the rails in a train track.

For me, whenever I do this visualization, the first width seems WAY bigger than the second. So trains should stick many feet out on each side of the track. But I know what trains look like, and that doesn't seem to be the case.

So... (a) does anyone else have the same visualization issue?
(b) can anyone point out which part of this I'm visualizing wrong?
Old 02-23-2017, 02:28 PM
scr4 scr4 is offline
Join Date: Aug 1999
Location: Alabama
Posts: 14,560
I've never seen a train with 6 seats per row. For Japan's shinkansen (same rail gauge as US and Europe), it's 5 seats (2 on one side and 3 on the other) for regular passenger cars and 4 seats for the "green car." In Europe it's usually 4 seats in 2nd class and 3 seats for 1st class, if I remember correctly. In the US it's generally 4 seats.

Also, trains do overhang quite a bit on both sides. The maximum train size is called the loading gauge and varies greatly by country, but as you can see in that link, it can be more than twice the distance between the rails. American bi-level trains like the Amtrak Superliner trains are 10' 2" wide, riding on rails that are 4' 8.5" apart.

Last edited by scr4; 02-23-2017 at 02:31 PM.
Old 02-23-2017, 02:33 PM
kenobi 65 kenobi 65 is offline
Corellian Nerfherder
Join Date: May 2000
Location: Brookfield, IL
Posts: 11,749
A passenger car (or, for that matter, any train car) certainly *is* considerably wider than the tracks.

Standard gauge in the U.S. is 4' 8 1/2". Now, that's the gauge at the *inside* of the rails (which is the relevant dimension, since that's the dimension in which the car's wheel flanges must fit); you would add a couple of inches on either side for the overall width of the rails, I suppose. And, depending on the exact width of the ties used, the tracks might *look* a foot or two wider.

Here's an example of a (fairly) new commuter car model, used by Metra (the Chicago-area commuter rail agency). You can see from the specification sheet that it's almost 9' 10" in width, which means that the outer width of the car is just over 5' wider than the rail gauge -- or, in other words, there's an "overhang" of over 2.5 feet on each side, if you compare the outer edge of the car to the location of the wheel flange.

Also, the interior of that rail car (I ride in one twice a day) is a center aisle, and a bench seat on either side of the aisle. Those bench seats are really designed for two passengers, not three, and I don't think you could get three in one unless they were both (a) very skinny (or children) and (b) very friendly.

The picture of that car certainly shows that there's a difference between where the outer edge of the car body is, and where the "outer edge" of the truck (the mechanism which holds the wheels and axles) is...and, then, there's also some depth to that truck, as well as between the outside of the wheel, and the flange. That said, I suppose that it doesn't *look* like 2 1/2 feet there, but that's what it is.

Last edited by kenobi 65; 02-23-2017 at 02:36 PM.
Old 02-23-2017, 02:34 PM
Riemann Riemann is online now
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 4,699
I share the visualization issue.

A little research seems to show that for the tracks/wheels, "standard gauge" is 4ft 8.5".
Then there is "loading gauge" for the width of the body of the train, see here:
In the U.S., standard width for a passenger train seems to be about 10.5 ft, which is consistent with a seat width of about 1.5ft, 6 seats and a narrow aisle.

I think, then, the visualization problem is that trains do not look as though they are 220% the width of the tracks.

Last edited by Riemann; 02-23-2017 at 02:36 PM.
Old 02-23-2017, 03:31 PM
jtur88 jtur88 is offline
Join Date: Aug 2011
Location: Cebu, Philippines
Posts: 14,329
Many such things seem deceptive., A basketball hoop is almost exactly double the diameter of a basketball but when a shot goes in, it looks like it barely fits.
Old 02-23-2017, 03:43 PM
pulykamell pulykamell is offline
Charter Member
Join Date: May 2000
Location: SW Side, Chicago
Posts: 44,458
Originally Posted by jtur88 View Post
Many such things seem deceptive., A basketball hoop is almost exactly double the diameter of a basketball but when a shot goes in, it looks like it barely fits.
Wow. That one does surprise me. A basketball is 9 1/2 inches in diameter. The hoop is 18 inches. And it's not like I've never played basketball to not realize this. Knowing a basketball is 9 1/2 inches, if I had to guess, I'd've guessed the hoop is somewhere around 14, maybe 15 inches.
Old 02-23-2017, 05:36 PM
erysichthon erysichthon is offline
Join Date: Sep 2012
Posts: 1,534
Originally Posted by MaxTheVool View Post
So... (a) does anyone else have the same visualization issue?
(b) can anyone point out which part of this I'm visualizing wrong?
I've notice the same thing, but can't explain it. Every time I'm on a train, I marvel at how roomy they are on the inside, in contrast to the narrowness of the tracks.
Old 02-23-2017, 06:27 PM
Fubaya Fubaya is offline
Join Date: Apr 2008
Posts: 3,898
Here is a photo of a train from more or less behind. Here is a photo from directly behind, although it's not a modern train. (there aren't many good train photos from behind so I resorted to searching for cabooses)

I wonder if all the stuff that's outside of the wheels helps contribute to the illusion. Here is a photo of the "truck" or "bogie", the thing that holds the wheels on a train. I have no idea how thick those metal bars and springs are (and they vary by model), but it wouldn't surprise me if they stick out a foot wider than the wheels. They're often appear to be more or less even with the body of the train, so a person taking a casual glance might assume the wheels are the width of the train. Just a theory.
Old 02-24-2017, 04:38 AM
kk fusion kk fusion is offline
Join Date: Sep 2008
Posts: 426
A TGV is 290 cm wide, giving it 73 cm overhang on each side, which looks about right from the outside.

The question remains why it looks so much wider from the inside. My guess is that our minds extrapolate to standard room height, which passenger compartments, especially in double-floor carts, don't have.
Old 02-24-2017, 04:55 AM
Isilder Isilder is offline
Join Date: Mar 2013
Posts: 4,305
You could drive a 10 foot wide passenger carriage down a 2 foot wide track.

Has it been done ? Not really, because narrow guage railways were built with platforms suited to narrow loading guage cars ... But in Queensland they needed locomotives to run on old fashioned sugar cane railways. They got them from NSW's standard gauge fleet.... Several standard gauge 73 class locomotives of the NSWR, which are 9 feet 3 inches (2.82 m) wide, had been converted for use on 610 mm (2 ft) cane tramways.. basically the entire track is suitable to carry a 10 foot wide, standard length loco or wagon , and they just have to be sure the wagons are balanced so that the COG remains inside the 2 foot wide track ( drop the COG down to the ground.. it has to remain inside the rails. Or else the rail acts as a pivot and the car rotates on it.) Also these cane sugar tramways have severe speed limits... When you add cornering's inertia the stability diagram, the force of cornering causes the COG to be dropped toward ground at an angle.. so it doesn't take much speed to cause the COG with cornering inertia (what some may call centrifugal force) included, to fall outside a 2 foot wide rail ...

Last edited by Isilder; 02-24-2017 at 05:00 AM.
Old 02-24-2017, 05:17 AM
AHunter3 AHunter3 is offline
Charter Member
Join Date: Mar 1999
Location: NY (Manhattan) NY USA
Posts: 19,777
Another possibly similar illusion: ever see a house's foundation before the walls go up? Does it look to you, as it does to me, like each room is no bigger than a pasteboard box and the entire house smaller than what you'd want as your bedroom?
Old 02-24-2017, 07:16 AM
kanicbird kanicbird is offline
Join Date: May 1999
Posts: 18,809
Just another chiming in that high capacity trains, such as commuter rails, is often 2-3 seating or 2-2 seating. I have never seen a 3-3 seating though if the airline industry ever got a hold of it I'm sure they would try.
Old 02-24-2017, 07:55 AM
Quercus Quercus is offline
Join Date: Dec 2000
Location: temperate forest
Posts: 6,878
My WAG is that it's mostly an interior/exterior perception thing. If you ever go into your yard and mark out the size of your bedroom (or any other room), it will seem incredibly small - how could you live in that space?. Interiors seem bigger perceptually than things outside.

Also, note that the track gauge is between the inner sides of the rails. When you look at a railroad car (especially when noticing how much overhand there is) you notice the outside edge of the trucks, which is quite a distance farther out than the inside of the rail.
Old 02-24-2017, 07:56 AM
Fotheringay-Phipps Fotheringay-Phipps is offline
Join Date: Mar 2009
Posts: 11,554
Part of it has to do with the fact that the train hangs over on both sides, and each side is individually not that great, but the two sides add up. The other part below.
Originally Posted by AHunter3 View Post
Another possibly similar illusion: ever see a house's foundation before the walls go up? Does it look to you, as it does to me, like each room is no bigger than a pasteboard box and the entire house smaller than what you'd want as your bedroom?
I was going to point this out as well. (I remember seeing foundations that looked like the size of decent sized houses that turned out to be an entire row of townhouses.)

IMO a lot of it - both in the case of houses and even more so in the case of trains - has to do with what you're measuring against. In the case of trains, when you see the rails you're measuring them against the train as viewed from the outside. The train when viewed from the outside is a very big object, and those rails look small by comparison. But when you're inside the train, you're measuring the space against yourself and other people and whatever other items are found in the compartment. These are relatively small, so the space looks bigger by comparison.

I think something similar is happening in the case of foundations. The foundation when viewed as an empty hole doesn't look all that big. But when the house is built, then you're measuring the space against people and furniture and the like, which are much smaller, and the same area seems a lot bigger.
Old 02-24-2017, 01:50 PM
guitario guitario is offline
Join Date: May 2013
Posts: 159
I have a similar perception thing with a new restaurant/cinema complex built on an old car park in my town. The car park was relatively small, yet somehow there is room to build a huge building that contains 10 cinema screens, 10 restaurants and a casino. Where is the room?

From this -

To this -

Yet I distinctly recall being in the car park and walking over to the other side in seconds.. yet now it fits 20 + large rooms in the same space, albeit over 2 floors, but still.. there's corridors and large open spaces inside too.. unfathomable to my useless visual perception abilities.


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump

All times are GMT -5. The time now is 04:57 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

Send questions for Cecil Adams to:

Send comments about this website to:

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Copyright 2018 STM Reader, LLC.

Copyright © 2017