Study Shows Stone Way "Road Diet" Improved Traffic, Safety

By Erica C. Barnett May 24, 2010

A new report by the city's transportation department (SDOT) finds that "rechannelizing" Stone Way North in Wallingford—essentially, adding a bike lane in the uphill direction and a shared-lane marking, or sharrow, on the downhill side—has made the street safer for drivers, pedestrians, and bicyclists. The change to Stone Way, like a similar change currently being considered for W. Nickerson St., was opposed by businesses who said it would lead to paralyzing traffic and clogged neighborhood streets in the area.

Instead, SDOT found, exactly the opposite happened:

• The percentage of drivers exceeding the 30 mph speed limit on Stone Way by 10 mph or more dropped about 75 percent—from about 4 percent to about 1 percent. A pedestrian struck at 20 mph, according to studies cited in SDOT's report, has an 85 percent chance of survival, compared to only 15 percent for a pedestrian struck at 40 mph.

• While car traffic on Stone Way decreased 6 percent after the road was rechannelized, bike traffic increased a whopping 35 percent, with bike traffic representing around 15 percent of rush-hour trips on the road.

Traffic on neighborhood streets did not increase, as some neighborhood residents feared; instead, it actually declined substantially, with traffic volumes as much as 49 percent lower on streets parallel to Stone Way. Only two parallel street segments showed any increase—one, Woodland Park Ave. N. at N. 42nd St., climbing by 2 percent (three cars) at morning rush hour, and the other, Woodland Park Ave. N. at N. 50th St., increasing by 27 percent (12 cars) at morning rush hour.

• Collisions between cars and cars, bikes, and pedestrians declined dramatically—14 percent—after the new bike lane and sharrow were introduced. And collisions causing injuries fell even further—33 percent. Finally, car collisions with pedestrians declined even more dramatically —fully 80 percent.

What are the implications for future "road diets" like the one proposed for Nickerson? Fans, like Mayor Mike McGinn, will certainly see the latest study as good news—more evidence that if you add bike lanes and pedestrian-safety measures to a road, traffic doesn't slam to a halt as a result.

For detractors, like businesses around proposed road diets, no amount of evidence is likely to be enough. Just this morning, North Seattle Industrial Association president Eugene Wasserman announced the formation of a new "15th Ave. W Transportation Coalition" dedicated, among other things to "protect[ing]" Nickerson "as a route to I-5 and the north portal" of the new Alaskan Way deep-bore tunnel. "Any proposal that reduces the carrying capacity of Nickerson is unacceptable." Even, it seems, when it doesn't.
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