With steel? I'd imagine that would add a hefty price on there, not to mention that the track would weigh a LOT more, resulting in the need for stronger supports. That'd be more money. Steel dosen't absorb sound either, if I'm not mistaken. I believe it carries it. Sand absorbs it, and that's why they use it to silence "the sound."
I think that the idea of using sand is cool. Kudos to B&M.
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I pledge defiance to the flag of the United States of America, and to the Republicans, which I can't stand, one nation, under smog, indespicable, with liberty for just us, not all.