Dear Cecil: I recently was sent this interesting story by an Internet friend. Is this true? Dave Shorr

Cecil replies:

Nothing I like better than getting to the bottom of some well-known bit of netlore. Dave attached the following, which has been making the E-mail rounds over the past year or two:

The U.S. standard railroad gauge (distance between the rails) is four feet, eight and a half inches. That’s an exceedingly odd number. Why was that gauge used? Because that’s the way they built them in England, and English expatriates built the U.S. railroads. Why did the English people build them like that? Because the first rail lines were built by the same people who built the prerailroad tramways, and that’s the gauge they used. Why did ‘they’ use that gauge then? Because the people who built the tramways used the same jigs and tools that they used for building wagons, which used that wheel spacing. 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, because that’s the spacing of the old wheel ruts. So who built these old rutted roads? The first long-distance roads in Europe were built by Imperial Rome for the benefit of its legions. The roads have been used ever since. And the ruts? Roman war chariots made the initial ruts, which everyone else had to match for fear of destroying their wagons. Since the chariots were made for or by Imperial Rome, they were all alike in the matter of wheel spacing. Thus, the standard U.S. railroad gauge of four feet, eight and a half inches derives from the specification for an Imperial Roman army war chariot. Specs and bureaucracies live forever. So the next time you are handed a specification and wonder what horse’s ass came up with it, you may be exactly right. Because the Imperial Roman chariots were made to be just wide enough to accommodate the back ends of two warhorses.”

Funny? Sure. True? Yes and no. Follow the line of development with me and you’ll see what I mean.

(1) U.S. track gauge based on UK track gauge. True. While most U.S. railroads were designed by U.S. engineers, not British expatriates, a number of early lines were built to fit standard-gauge locomotives manufactured by English railroad pioneer George Stephenson.

(2) UK railway track gauge based on width of earlier tramways used to haul coal. More or less true. Although tramway width varied widely among regions, those in the coal district in the north of England, where Stephenson began his work, used a gauge of four-foot-eight.

(3) North England tramway width based on wagon-wheel spacing. Not literally true — there was no standard wagon-wheel spacing. However, wagons and their wheels averaged five feet in width, since this size would conveniently fit behind a team of draft animals. The North England tramway gauge apparently had been arrived at by starting with an overall track width of five feet and using rails that were two inches wide. Five feet minus four inches for the rails equals four-foot-eight. (I’m skipping some complicated history here, but that’s the gist of it.) Stephenson later widened the tracks a half inch for practical reasons, making the standard gauge four feet, eight and a half inches. While this is an “exceedingly odd number,” it derives from a basic track width of five feet, which is not odd at all.

What about Roman war chariots and rutted roads? Roman “rutways,” many of which were purposely built to standard dimensions, were close to modern railroad tracks in width. For example, the rutways at the buried cities of Pompeii and Herculaneum averaged four-foot-nine center to center, with a gauge of maybe four-foot-six. But there’s no direct connection between Roman rutways and 18th-century tramways. The designers of each were dealing with a similar problem, namely hauling wheeled vehicles behind draft animals. So it’s not surprising they came up with similar results. (Thanks to University of Munich economic historian Douglas Puffert, an expert on railroad gauge, for kind assistance in tracing this story.)

Bonus info! I didn’t have room in the printed column, but another version of this legend adds the rococo touch that the solid rocket boosters (SRBs) used on the space shuttle are manufactured at a Thiokol plant (I presume in Utah), then shipped to Florida by rail for final assembly at the launch site. The rail line passes through one or more tunnels en route, and the SRB pieces had to be made small enough so they’d fit through the tunnel bore. Thus, the legend triumphantly concludes, the dimensions of one of our most advanced vehicles was determined by the size of one of our most ancient!

True? Again, yes and no. A NASA spokesperson confirms that railroad tunnel dimensions were a constraint that had to be taken into account when designing the SRBs. However, tunnel dimensions are less a function of track gauge than of rolling stock width. U.S. railroad cars are quite a bit wider than those in England because parallel tracks are placed farther apart. (I’m talking tracks, not rails here, capisce?) As a consequence, U.S. railroad tunnels typically are wider too. So you can’t really make the case that the size of the space shuttle’s boosters was determined by the width of a couple horses’ butts.

More bonus info! I came across the following in the book Gordian Knot: Political Gridlock on the Information Highway by W. Russell Neuman, Lee McKnight, and Richard Jay Solomon:

[A]s an accident of history most road carriages in the the Middle Ages inherited the old Roman cart gauge of approximately 4 feet, 8-1/2 inches. Julius Caesar set this width under Roman law so that vehicles could traverse Roman villages and towns without getting caught in stone ruts of differing widths. Over the centuries this became the traditional standard.

Richard Solomon, the source of this bit, has elaborated in a message posted to the net that Caesar decided on standard gauge after seeing a “grooveway” at the isthmus of Corinth in Greece. This was a purposely built set of ruts used to guide the wheels on carts carrying goods being transshipped across the isthmus. Prof. Solomon says he personally measured an excavated portion of this ancient grooveway and found it had a gauge of four feet, eight and a half inches.

Coincidence? That was my reaction. But this claim about an edict by Julius Caesar was something new — it’s not mentioned in any of the standard histories of Roman roads I’ve seen. I’ve exchanged E-mail with Prof. Solomon trying to learn his source, but he was on the road and couldn’t provide a cite. Watch for late-breaking bulletins as your columnist continues to pursue this story.

One last thing. I have heard tell of certain wheel ruts having a gauge of you-know-what at the gate to an old Roman fort called Housesteads on Hadrian’s Wall in the north of England. Legend has it that George Stephenson based the gauge he used for his locomotives on the width of these ruts. Here’s what Housesteads by James Crow (Batsford, London, 1995, pp. 33-34) has to say on the subject:

The gauge between the ruts is very similar to that adopted by George Stephenson for the Stockton to Darlington railway in 1837 and a ‘Wall myth’ developed that he took this gauge from the newly excavated east gate. There is a common link, but it is more prosaic and the ‘coincidence’ is explained by the fact that the dimension common to both was that of a cart axle pulled by two horses in harness (about 1.4m or 4ft 8in). This determined both the Roman gauge and Stephenson’s, which derived from the horsedrawn wagon ways of south Northumberland and County Durham coalfields.

Just as I said.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.