> An added question is whether people speed more in a closed community or in a grid.

I live on a cul de sac and not a day goes by that I don't see someone speeding through the stop sign a few houses down. The cul de sac is not what appealed to me about where I'm living, and I would gladly give it up so I could ride my bicycle unimpeded to the subway station that's nearby without being forced out to the major highway that runs through the area.