When, exactly, is getting stuck in traffic a good thing? When it's a sign of an economic recovery, according to Kirkland-based traffic information firm INRIX. The firm reported today that its tracking of traffic shows "optimism" for the U.S. Economy, with traffic congestion a decline of three percent. That compared with apparently a "dramatic" 20 percent drop in traffic congestion from December 2010 to December 2011, which INRIX said was a sign of a slowdown in the economy. INRIX has recently been calculating what it calls a INRIX Gridlock Index (IGI) score for various cities in the U.S., in an attempt to help provide another source of economic data.