It substantially increases pedestrian wait times though. In a grid city if I'm headed north east, I opportunistically take north or east, whichever is available. So I have no wait time at all for most of my journey, until the part when I have to go only north (say). A grid makes this the typical situation and placing a wait at every light makes the journey very tedious. It also slows down cars, of course. I'm sure this is the main reason it's not done - whether it's worth the risk, I'm not sure.