This story in the Seattle Times shows tolls on 520 could be as high as $3.50 each way during the peak times, or $7 round trip. Within 5 years, the toll could hit $8.70 for a round trip.
The story goes on to question the impact on traffic and how many people will divert to other roads or skip driving all together.
But the WSDOT conducted a feasibility study on this very topic in 2007. It shows that tolls on 520 would increase traffic volumes on I-90 by 13 percent by 2015. The toll amount assumed to create a 13 percent diversion to I-90 was $2.15 (am peak) and $2.65 (pm peak) for an average one way toll of $2.40.
So a one way toll of $3.50 on 520 would mean traffic volumes on I-90 would grow to a rate higher than 13 percent.
Based on the WSDOT study, every .18 cents in tolls roughly equals about 1 percent of additional traffic volume to I-90. So an average one way toll of $3.50 on 520 will increase traffic volumes on I-90 by about 20 percent.
Another WSDOT study shows traffic volumes on I-90 will increase about 25 percent when Sound Transit converts the centers lanes to light rail.
Once again, policymakers demonstrate that traffic congestion relief is not a goal in Washington state.