A survey by the Brookings Institution rated the Washington region as the most walkable urban area in the country. Such findings are put to the test by Peter Owen, a lawyer and former chairman of a citizen advisory commission on transportation in Arlington. He works near Union Station and lives in Clarendon. Several times a week, he walks home. Owen has more than a half-dozen basic routes, which can take him across the Roosevelt, Memorial or Key bridge. I tagged along on Oct. 24. The temperature was in the mid-50s. The sun set at 6:17 p.m.