New traffic count analysis compiled by the Seattle Department of Transportation shows that between 2006 and 2008, traffic volumes on streets citywide generally decreased, with the most consistent overall decline in downtown Seattle, where nearly every street showed lower traffic volumes as of two years ago (the most recent year for which information is available.)

Although traffic on some specific streets did increase over the three-year period (notably Martin Luther King, Jr. Way South, where traffic was consistently up), the vast majority of the city saw traffic decline. In places like downtown, the decline means that some streets are only being used at 25 to 50 percent of their overall "capacity"—the total number of cars a street can hold without becoming gridlocked.Last year, the Sightline Institute, a local environmental and land-use policy think tank, released a report that partially explains why traffic might have decreased even as population continued to rise.

According to the study, increasing gas prices have contributed to decreasing per-capita gas consumption, as well as a decrease overall in the number of miles people drive (vehicle-miles traveled). However, increasing gas prices aren't the only factor causing people in the region to drive less; improved transit ridership, better fuel efficiency, and smarter land use and transportation policies are making it easier to forgo trips or use alternatives to driving.

Given that this trend seems unlikely to reverse itself, why are we building two massive new highways (the waterfront tunnel, which won't carry any transit, and the new 520 bridge, which as proposed would include six new lanes for cars?

Cary Moon, head of the pro-transit, anti-tunnel People's Waterfront Coalition, puts it this way: "We have plenty of pavement in this city if we just use it more efficiently. It is mind boggling to see all these five and six lanes streets north of downtown with only 30 percent to 50 percent of their capacity used."

The Seattle Department of Transportation says it will provide more analysis on the new traffic numbers tomorrow morning.