Much as I love that story about the gauge of railroads, snopes doesn't
seem to think much of it. See <a href="http://www.snopes.com/history/
american/
gauge.htm">gauge</a>

Here's one I heard on the radio, possibly on Prairie Home Companion:

Why does a chicken coop have two doors?
|
|
|
|
|
|
|
|
Wait for it...
|
|
|
|
|
|
|
|
\|/
Because, if it had four doors, it'd be a chicken SEDAN!