Why are US Railroad tracks 4'-8 1/2 wide?

Question

Why is this particular gage used for the US Railraod system

Answer 1

So the wheels will fit....

Answer 2

Standard gauge ( 4' 8 1/2" ) is what George Stephenson used on the first railway, the Liverpool and Manchester railway.  I don't think it is known why he chose that width, but this was adopted on all railways in England due to his influence and the need for standardization.

Early RR equipment in the US was bought from England (and Stephenson) but even still, well into the 1860s we didn't have a standard gauge. This was mostly true in the South and it was only after the Civil War that a decision was made to standardize especially since the South's railroads needed rebuilding due to being destroyed during the war.

Answer 3

The siding of steel used in freight cars was a particular size (?). To prevent cutting steel to a different size they made tracks wide enough to structurally support the weight and size distribution of the cars riding on top of the rails.