From There and back again in The New Yorker:
I was shocked to find how robust a predictor of social isolation commuting is,” Robert Putnam, a Harvard political scientist, told me. (Putnam wrote the best-seller “Bowling Alone,” about the disintegration of American civic life.) “There’s a simple rule of thumb: Every ten minutes of commuting results in ten per cent fewer social connections. Commuting is connected to social isolation, which causes unhappiness.
Erin’s commute on days when she misses every stop light is 12 minutes. On good days, it’s eight minutes. My commute, generally speaking, consists of me walking downstairs.