Who Spec’d This?

A History of Specifications 

When you see a space shuttle sitting on the launch pad, there are two big booster rockets attached to the sides of the main fuel tank.  These are the solid rocket boosters, or SRBs.

The SRBs are made by Morton Thiokol at a factory in Utah.

Originally, the engineers who designed the SRBs wanted to make them much fatter than they are. Unfortunately, the SRBs had to be shipped by train from the factory to the launch site in Florida and the railroad line runs through a tunnel in the mountains.  The SRBs had to be made to fit through that tunnel. Now, the width of that tunnel is just a little wider than the U.S. Standard Railroad Gauge (distance between the rails) of 4 feet, 8.5 inches.

That’s an exceedingly odd number.  Did you ever wonder why that gauge was used?  Because US railroads were designed and built by English expatriates, and that’s the way they built them in England.

Okay, then why did the English engineers build them like that?

Because the first rail lines of the 19th century were built by the same craftsmen who built the pre-railroad tramways, and that’s the gauge they used.

I’ll bite, why did those craftsmen choose that gauge?  Because they used the same jigs and tools that were previously used for building wagons, and you guessed it, the wagons used that wheelspacing.

Now I feel like a fish on a hook!  Why did the wagons use that odd wheel spacing?

Well, if the wagon makers and wheelwrights of the time tried to use any other spacing, the wheel ruts on some of the old, long distance roads would break the wagon axles.  As a result, the wheel spacing of the wagons had to match the spacing of the wheel ruts worn into those ancient European roads.

So who built those ancient roads?

The first long distance roads in Europe were built by Imperial Rome for the benefit of their legions.  The roads have been used ever since.

And the ruts?

The initial ruts, which everyone else had to match for fear of destroying their wagons, were first made by Roman war chariots. And since the chariots were made by Imperial Roman chariot makers, they were all alike in the matter of wheel spacing.

Well, here we are.  We now have the answer to the original question.  The United States standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman army war chariot.

Specs and bureaucracies live forever.

That’s nice to know, but it still doesn’t answer why the Imperial Roman war chariot designers chose to spec the chariot’s wheel spacing at exactly 4 feet, 8.5 inches.

Are you ready?

Because that was the width needed to accommodate the rear ends of two Imperial Roman war horses!!!

Well, now you have it.  The railroad tunnel through which the late 20th century space shuttle SRBs must pass was excavated slightly wider than two 1st century horses’ butts. 

Consequently, a major design feature of what is arguably the world’s most advanced transportation system was spec’d by the width of a horse’s behind!

So, the next time you are handed a specification and wonder what horses’ rear end came up with it, you may be exactly right. Now you know what is “behind” it all.

~Author Unknown~