They saw the signs, that the highway was closed to vehicle traffic, permanently, from then on,
and that it was done, because they had no choice, in order to be safe for the hundreds of people there daily, kneeling to spell words?
I know this is not the answer to the riddle, but it's such a funny image in my mind! No one would be able to resist going over there,
just to spell out a word or two.....or lots of words!