daestrom wrote:

"Sawney Beane" wrote in message
...

Our RR gage came from the width of Roman chariots? (I wrongly
called the width the wheelbase.) The evidence for the myth is that
ruts in the Roman pavement coming out of a stone quarry are as far
apart as modern rails. Saying that was the width of chariots is
like saying jeeps and humvees have the same width as each other and
as eighteen-wheelers.

Maybe each of the early railroad builders used a different Roman
chariot as his gage, and that's why there were so many widths.
They may have been relatives of Click and Clack.

The outside measurement of modern rails is very close to five feet.
I think the original specificaton, in the days of wooden rails,
was for wheels five feet apart at the outside. Wheels and rails
evolved, but new wheels had to fit old rails and new rails had to
fit old wheels. I think that evolution is why the outside
measurement is slightly different from five feet nowadays.

In the US, the most widely used gage was 4' 8 1/2" measured between the
*inside* faces of the rails.

Now you know why I had to go back and measure again: I got confused
between inside, outside, and center-to-center.

This was chosen because most of the early
locomotives were brought over from England, and that was the gage used
there.

Two locomotives were brought from England in 1829. They were too
heavy for American tracks. In England, Robert Stephenson
demonstrated the Rocket in 1829. In America, Peter Cooper
demonstrated the Tom Thumb in 1830. Robert Stephenson and Company
built the Stevens, now known as the John Bull, for the Camden and
Amboy RR. It went into service in 1831. It's the earliest
surviving steam locomotive, and it has the 4' 8.5" gage.

Not many locomotives were imported. American locomotives were
lighter than English ones and rode American rails better because
the frames were inboard of the wheels.

This page tells where Stephenson got his gauge:
http://www.straightdope.com/columns/000218.html

In the part of England where Stephenson worked, wagons averaged
about five feet because that was the approximate width of two
horses' asses. He laid his rails five feet apart, outside. They
were two inches wide, which put them 4' 8" apart, inside. For
practical reasons he widened it another half inch. I think it had
something to do with flanges and binding.


Some other gages were used for specialty service, such as mining and
logging. When railroads started interchanging, they had to standardize and
they chose the most common gage. So for the US and Canada, it has been 4' 8
1/2" now for over a hundred years.

daestrom

The Federal Government said the gage of the Transcontinental
Railroad would be 4' 8.5". That became the national standard in
the 1880s.