This has gone on too long -- I'm writing a last reply here in public and then I would ask that we take this to private mail. smb@research.att.com says:

Why did virtually all the railroads in the northern U.S. use the same rail gauge BEFORE regulation of the railroads?

Ah -- you specify the ``northern'' U.S. The situation in the south was very different.

Yes, the south had fewer railroads and they followed a different gauge -- this is to be expected in such situations.

And even in the north, the Pennsylvania Railroad was so large (they're the ones who billed themselves as ``the standard railroad of the world) that other folks had to follow if they came near the PRR. It was near-monopoly that created that situation, not any desire for co-operation.

I once read a wonderful account of how enraged J.P. Morgan was one day when, while relaxing at his country home on the Hudson in upstate New York, he heard the sounds of a railroad construction gang driving through a railroad competing with the Penn Central line which he effectively controlled via the Vanderbilts. No attempt to set up a railroad cartel or monopoly worked until the ICC was formed, you know -- a government agency created largely so monopolists would have a legal way of enforcing rate fixing.

In Europe, there are still a variety of different gauges, electrical standards, loading gauges, etc.

Yes. Such things typically occur for a while when people aren't geographically proximate and don't interact much -- the north and south were such an example. However, in regions where people do interact standards quickly enforce themselves. Look around you at the computer industry for example. Perry