Puckdropper puckdropper(at)yahoo(dot)com wrote in
eb.com:

John McCoy wrote in
:

Puckdropper puckdropper(at)yahoo(dot)com wrote in
eb.com:

*snip*

Train speeds much over highway
speeds (70 in many places, 75 in others) require the use of concrete
ties.

No, you can use wood or concrete at any speed. It's the weight
and number of trains that makes a difference, not the speed
(speed limit for freight trains is 69mph, for passenger 79mph
except for a handful of "high speed" lines. As you might guess
by the weird numbers, those are set by the Federal government).

While that's true from a physics standpoint, I believe it's also a
government requirement that higher speeds be done only on concrete
ties. It's been a while since I came across it, but speeds above
something like 100 mph required concrete ties and full grade
separation.

Hmm, not sure if that's a FRA requirement or not - it's been a
while since I was involved with that stuff, and there's two
different things the government calls "high speed" (one being
anything over the normal 79mph limit, and the other being Acela
style 150mph speeds) which have different rules.

Definately all forms of high speed require enhanced signalling
and grade crossing control, with Acela speeds needing grade
seperation. And now, of course, PTC will be required.

As a practical matter, you'd use concrete ties, whether required
by regulation or not.

The explanation I read years ago about the speeds were based on
highway speeds + 15 mph, which is considered the threshold for
wreckless driving in some states. 65 + 15 = 80, minus 1 is 79. (Thus
"safe". ha ha ha)

In the case of trains it's because the Federal regs use the
phrase "less than". Passenger trains must operate at less
than 80mph. So the railroads, logically enough, set 79mph as
the speed limit. In cases where the Fed rules don't apply,
they use multiples of 5 like everyone else.

John