it seems to me it's not only density but mobility too. The US is a very mobile place, people can move around very easily. I think you have to consider that along with density when looking at how fast a virus can spread.

I hope a side effect of the virus spread is proving wfh feasible to many skeptics. Working from home goes a long way to reducing pollution and increasing productivity and morale. It's definitely not one size fits all and doesn't work for all personalities and jobs but it should be used where it can work. At a min, it keeps people off the roads/tracks.