"Standard gauge" is indeed 4' 8-1/2". Other gauges were used early on, and some survive elsewhere in the world. In the USA, the Erie Railroad was originally built with 6 foot gauge, and before the Civil War, railroads in the northern USA were mostly 4 foot 9 inch gauge while railroads in the southern USA were mostly 5 foot gauge. Then, in the 1870s-80s, there was a big push to standardize.
The Philadelphia Market Frankford Line (The El) is broad gauge 5' 2 1/2", but the Broad Street subway is standard gauge.
Rode the Brill Bullets on the Norristown High Speed Line right before they were retired. That was a thrill!
Ever ride or see the Liberty Liners there? https://www.classicstreamliners.com/npt-liberty-liner.html https://en.wikipedia.org/wiki/Electroliner (The Red Arrow acquired them from the North Shore railroad about 1964, did some conversion and ran them until 1978. They were air-conditioned and had a restroom and a tavern-lounge car - riders could get a hot drink and a breakfast snack in the morning, and a snack and soft or not-so-soft drink in the evening. I never got to ride one but rode the other stuff once in a while. NHSL has been modernized and there are plans to extend it to King of Prussia.
End of 2018 we had an interesting rail trip, Giza to Luxor On Egypt Rail. 9 1/2 hours scheduled, it took a bit longer, but overnight in a sleeper. Actually twice, we returned the same way. Interesting to say the least. https://www.seat61.com/Egypt.htm#Cairo - Luxor - Aswan Scroll down for the pictures. I think they used a wide angle lens, the compartment seemed tighter, especially with the luggage in there. Restroom at the end of the car (Can't be used while in the station - no holding tank.) Our train did not have the lounge car.
On a couple of the crusty old railroads around here, you can watch the rails move down and then up as each wheel passes over... Must be 3-4 inches of travel at least.
That's not uncommon for low speed track. As long as the gage width is within tolerance we're good to go...
