Did you ever wonder just how some specifications or rules come to exist? Well, there are probably lots of reasons that are long forgotten, but the example below demonstrates how odd things get carried forward. (If you think this is made up, just consider all the effort that has been required on Y2K merely because the first programmer took a shortcut with the date.)

The U. S. Standard Railroad Gauge (distance between the rails) is 4' 8½". That is an exceedingly odd number. Why was that size used?

Because that's the way they built them in England, and the U.S. railroads were designed & built during the Industrial Revolution by English expatriate engineers to accommodate English-built locomotives.

Why did the English build them like that?

Because the first rail lines were built by the same people who built the pre-railroad tramways, and that was the gauge they used.

Why did they use that gauge then?

Because the people who built the tramways used the same jigs and tooling that they used for building wagons, which used that wheel spacing.

Okay, why did the wagons use that odd wheel spacing?

Well, if they tried to use any other spacing the wagons would break on some of the old long distance roads in Europe and England. This was due to the old wheel ruts worn into the roads. The first long distance roads in Europe were built by Imperial Rome for the benefit of their legions. The thoroughfares have been used ever since.

And the ruts?

The initial ruts, which everyone else had to match for fear of destroying hitched wagons, were first made by Roman war chariots. These chariots were designed to be pulled by two horses hitched side by side. In order to roll smoothly, the chariot wheels had to be spaced far enough apart to avoid the hoof marks left by the horses, yet not protrude past the flanks of the horses to prevent entanglement with opposing traffic or roadside vegetation. Since the chariots were made for or by Imperial Rome, they were all alike in the matter of wheel spacing.

Thus we have the answer to the original questions. The United States Standard Railroad Gauge of 4' 8½" derives from the original specification for an Imperial Roman army war chariot. Two thousand years later and a continent away, the track layout of the entire U.S. railway network is based upon the fact that Imperial Roman chariots were made to be just wide enough to accommodate the rear ends of two war horses.

So the next time you are handed a specification and wonder if some horse's ass came up with it, you may be exactly right.

POSTSCRIPT

Apparently, the width of most railroad tunnels is defined by the width of trains, which is defined by the width of the tracks.  So far this makes sense.  But on top of this, the solid-fuel rockets used for the space shuttle are of a slightly narrower than optimal width.  Why? -- because they had to fit through a train tunnel, on the back of a cargo train, between their place of manufacture and launch.  So our space-age technology is limited by the Roman's horse's-ass guide to road width ...  and so it continues.  :)

The Road Less Travelled
    by Robert Frost

Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;

Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,

And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.

I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I--
I took the one less traveled by,
And that has made all the difference.