They do have a way of changing the carriages so that trains can pass from China to Russia. I assume they have the same provisions at the North Korean border with Russia.
How MIL Specs Live Forever
The US Standard railroad gauge (distance between the rails) is 4 feet, 8.5 inches. That's an exceedingly odd number. Why was that gauge used? Because that's the way they built them in England, and the US railroads were built by English expatriates.
Why did the English people build them like that? Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gage 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.
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, 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 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. 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 feet, 8.5 inches derives from the original specification (Military Spec) for an Imperial Roman army war chariot. Mil 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 war horses.
Professor Tom O'Hare
Germanic Languages
University of Texas at Austin
Space-Age Addendum
The next time you see the Space Shuttle sitting on the launch pad, take a look at the two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs. The SRBs are made by a company called Thiokol Propulsion, at their factory in Utah. The original engineering design for the SRBs called for them to be a bit fatter and a little shorter, but the SRBs had to be shipped by train from the factory to the launch site.
The railroad line from the factory passed through a tunnel in the mountains. The tunnel is only slightly wider than the railroad track, and the railroad track is about as wide as two horses' behinds.
So, a major design feature of what is arguably the world's most advanced transportation system was determined over 2000 years ago by the width of a horse's behind.
Ken Kuller