At a briefing for the media this morning (full disclosure: The assembled "media"=me), Seattle Department of Transportation traffic manager Eric Widstrand laid out the data SDOT collected in 2009 on traffic, collisions, and the number of people who are walking and biking in the city.

Stick with me, because it's fascinating stuff!

• The biggest thing that's changed in Seattle over the past decade or so is that average daily traffic (vehicles, not bikes or peds) has gone down even as the city's population has increased---from a high of about 980,000 cars a day in 2003 to around 900,000 in 2009. At the same time, the number of people commuting by bicycle has gone up dramatically, increasing 15 percent between 2007 and 2009 alone.

• The report didn't look specifically at the Alaskan Way Viaduct, but they did count about 86,000 cars using Aurora north of Harrison St., an area that includes the viaduct. That's significantly lower than the 110,000 car estimate used by supporters of the deep-bore tunnel, and could provide fodder to tunnel opponents in making the case that Seattle doesn't need a highway on its waterfront.

• Even as  bike ridership went up, the percentage of bike commuters involved in collisions went down. The city's bike master plan, adopted in 2007, has a goal of reducing bike collisions by a third by 2017.

• Some specifics on those collisions: Although people age 15 to 24 make up only 14 percent of the city's population, they accounted for 24 percent of bike collisions in 2009. Statistically, the most dangerous time and day to drive last year was evening rush hours (between 4 and 7 pm) on Wednesdays. Most collisions occurred when a cyclist was riding with the flow of traffic, which is how, by law, they're supposed to ride. The largest proportion of crashes between cars and bikes (160 out of 382 reported) happened when the driver failed to yield the right-of-way to a cyclist. Out of those 382 collisions, the cyclist was wholly or partly at fault just 154 times; the driver was at fault 295 times.

• Somewhat surprisingly, given King County's helmet law, just 62 percent of bicyclists involved in crashes in 2009 were definitely wearing helmets (22 percent definitely weren't, and in 16 percent of crashes, the city doesn't know whether the cyclist was wearing a helmet or not.)

• Car collisions with pedestrians were also down, but they remained more common than bike collisions, with 479 crashes (11 of them fatal) last year alone. Sixty-eight percent of the time, the pedestrian was hit in a crosswalk (just 8 percent of all crashes were pedestrians crossing intersections against the signal).

• Although pedestrian and bike collisions were the most likely collisions to be fatal (accounting for 11 of 24 fatalities), overall, driving a car remains the most dangerous way to get around. Ninety-three percent of all accidents in 2009 were between cars or cars and stationery objects (like parked cars, which accounted for 24 percent of all car-on-car crashes, or things like phone poles and street signs, which made up another 6 percent).

• Finally, the data suggest that if you're going to get drunk, just stay home. Although just one cyclist was hit by a drunk driver in 2009, five drunk cyclists were involved in crashes, along with 11 pedestrians. (Two pedestrians "had taken medication," one was under the influence of drugs, and one was "apparently asleep," according to the report.