Hi Guys, I cannot understand a sentence in page 15-11 in Ballast Review Manual. The sentence is "if vertical clearance of an area adjacent to an accessible route is reduced to less than 80 in, a guardrail or other barrier must be provided." I don't know why. And what's the relationship of a guardrail or other barrier with the height of vertical clearance? I hope someone can give me an answer. Many thanks!
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