Here in Edinburgh, there are moves afoot to remove alot of the road signs from the city centre at least, not beacuse there are too many and they're hard to read, which they are, but because it helps the streets look more Georgian, in line with the World Heritage site status....

Kendell, I was trying to state the general case without going into numbers, as, as that link shows, doing so is probably a thesis at least. But if you want to be picky:

Elderly: Is 70 an unreasonable age to use here? By defining any particular age as elderly, there will be some people above that age who are fit and well, and in better shape than those half their age, and also those below that age who are suffering whom you would assume are decades older than they are, again in terms of their generall fitness.

Significant: Well, even one driver on the road has very slow reaction times, memory lapses or impared vision, that is significant for them, and anybody around them.