Re: Numerical Mysteries

57 inch gauge was really common. Maybe it still is. The PRR was somewhat unique in being deliberately built as such, but lots of other railroads ended up that gauge in a more roundabout manner. When the southern railroads changed from 5 foot gauge to standard during the late 1880's, they did so by moving one rail inward three inches--leaving them 4 foot 9 gauge. Of course it was interchangeable as many decades of seamless operation attests. Track gauge could commonly be widened as much as an inch or so on curves, and perhaps more in special cases.

Ohio gauge of 4 foot 10 was common during the 1830's and 1840's, but disappeared after some derailments were blamed on the difference between it and the more common 56.5 inch gauge. It's far more likely that poor construction standards, inadequate materials, and bad maintenance were the true culprits of those wrecks.

1/2 inch play on locomotive wheels was pretty standard 19th century construction practice.