On Thu, 20 Jan 2005 18:33:32 -0500, M. Adam Davis wrote:

> If you watch a section of track while a train loaded with coal or ore
> going over, you'll notice the rails and ties moving up and down on the
> order of 2-3 _inches_ as the wheels travel over them.

I don't think this is the case for all tracks. I used to live near a
track that would see trains of 100 ton coal cars up to a mile long,
many times a day. For the most part, the track was very stable -- very
little flexing. The only place where this was not the case was at
grade level crossings, where it looks like the ballast was not
properly done. The constant pounding of the trains had forced water
and mud up from down below, giving the 2 to 3 inches of flexing that
you mentioned above. Maybe these tracks were better built -- their
sole purpose is basically for hauling coal.
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