You know how some intersections in some cities have digital count-downs, telling you how many seconds you have to cross before the
walk signal changes to
don’t walk? How do they come up with the times?
I just waited at a corner, and when the
walk signal came on, the timer started at 47. Who decided that it should be 47 seconds, and not, say, 45, or 50? And why? Is there really any sense in which 47 seconds is enough, but 45 isn’t, and 50 is too long? Why should two or three seconds one way or another matter?