An observation that confronted me recently: when driving on a bridge that passes above the Capital Beltway, that eight lane thoroughfare seems far narrower than when one is on the Beltway itself (or when one is driving beneath the highway through an underpass.) Why?

When it happened to me in an unfamiliar neighborhood I actually couldn't believe, at first, that the road I was crossing above was a major interstate highway. It seemed somehow 50% too small, like a scale model. I don't think the problem is explained by simple masking, the edge effects caused by the bridge's abutments.

Could this be related in some way to the "rising moon" illusion? Or to the false size difference that appears when two arcs are nested one above the other? I'm mystified ...

TopicScience - 2004-03-30

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