Walking in Phoenix is an act of shame. You don't walk here because you reject car culture and all its dirty geopolitical and environmental implications. You walk because you can't afford not to. Everyone who sees you using the sidewalk knows this  -- drivers stopped at the light, folks cutting you off in the crosswalk, fellow passengers on the bus. So you avert your eyes, keep your head down, try to ignore the drivers lined up beside you in rush hour traffic. A few proud contrarians can hold their heads up and strut in the face of social judgment. Maybe they've saved half the money for a used Kia Rio and know that soon, with enough overtime at Costco and no more library fines for late DVDs, the privilege of sitting idle on congested surface roads in 100 degree heat will be theirs. Me? I walk fast, and carry