HOW IT ALL WORKS - All Aboard: The Complete North American Train Travel Guide - page 173

lar problem. Operating a freight train up such a grade is more
complicated, because they're a lot heavier and a lot longer. The
steepest grade on any mainline track in the United States is 4.7
percent. That's crossing the Blue Ridge Mountains near Melrose,
North Carolina. How steep is that? Well, railroaders consider
anything more than 1.8 percent to be mountain grade .
With a train, down can often be a much bigger problem than
up . The whole principle of a steel wheel on a steel rail is to reduce
friction to a minimum in order to move those massive weights.
That's well and good, but the result is what's called a lack of roll-
ing resistance—it simply means that once a train gets rolling, it
can be hard to stop. If it's coming downhill, even a hill that would
be unnoticed by the driver of an automobile, a train can react like
a roller coaster and accelerate. As I've mentioned elsewhere, an
engineer can frequently find him- or herself at the head of a long
train that's actually going downhill and uphill—trying to speed
up and trying to slow down—all at the same time. So how does a
freight engineer handle a train? The same way a porcupine makes
love: very carefully.
Keep to the Right
Where there is double track—that is, two tracks running parallel
to each other—trains usually stay to the right. There are excep-
tions, as you will probably notice, but they are usually caused by
track work of some kind.
Speed Limits
In most parts of the country, the maximum speed allowed for
Amtrak trains is 79 mph. Why 79 and not 80, you ask? Well,
federal regulations require that any train operating at 80 mph or
faster must have a device in the locomotive cab that picks up and