I've seen them taken down for repairs, and they're much larger than I'd thought, but not 7 feet tall. Maybe 4' IIRC?

The lenses are either 8" or 12" in diameter in the US: http://mutcd.fhwa.dot.gov/htm/2003r1r2/part4/part4d.htm

So if you're looking at 3 8" lenses in a row vertically, the whole thing is at least 3' tall, probably more.

I just looked through hundreds of photos of traffic lights on google, and not one was of the standard yellow US kind that hangs from a wire.