One week after the state started tolling the SR-520 bridge across Lake Washington, Sightline's Clark Williams-Derry writes, not only is traffic on 520 itself "a breeze," but traffic seems to have eased on I-5, and perhaps I-405, the two north-south routes that connect 520 to parallel (and untolled) I-90, as well. That conclusion is based on traffic volumes during the Wednesday morning rush hour---typically the heaviest-traffic period of the week.

(Images are from four weeks before tolling started and this morning. Sightline's scrolling version of this map is available here.)





Meanwhile, traffic on I-90 was slightly heavier than usual, but only a little; according to the state Department of Transportation, traffic volumes on I-90 increased just 8 percent on Wednesday morning, and while speeds were down, that was partly due to heavy rain and multiple accidents.

While it's still too early to reach any conclusions about travel patterns across the bridges, Williams-Derry notes that based on the evidence so far, as well as his own experience on the bridge, it appears that "the 520 tolls have shifted traffic patterns dramatically.  And that provides at least some evidence that tolls really can be an effective tool in managing congestion and traffic flows."

Additionally, he notes that if people are choosing to change their behavior in a way that reduces overall traffic volumes---by taking the bus, traveling at different times, carpooling or vanpooling, avoiding trips, or using other travel modes---then it's debatable whether we actually need all the expensive new road projects that tolls are supposed to pay for.

"http://www.wsdot.wa.gov/News/2012/01/05_SR520_Driverstweakcommute.htm