Study says half of drivers will divert from SR-520 bridge when tolls begin

Officials from the Washington State Department of Transportation were ready for spillover traffic from tolls on the SR-520 bridge onto other roads, but a new study says as much as 50 percent of all 520 drivers will travel elsewhere. The study, released Thursday, says daily trips on 520 will drop to 52,000 from the more than 100,000 average drives. This would not damage the state's revenue forecast from tolls to pay for $1 billion worth of the $4.65 billion replacement and improvement on 520, according to the study, because increased congestion on other roads could push drivers back to the tolled road.

September 12, 2011 2:00 pm

Officials from the Washington State Department of Transportation were ready for spillover traffic from tolls on the SR-520 bridge onto other roads, but a new study says as much as 50 percent of all 520 drivers will travel elsewhere.

The study, released Thursday, says daily trips on 520 will drop to 52,000 from the more than 100,000 average drives. This would not damage the state’s revenue forecast from tolls to pay for $1 billion worth of the $4.65 billion replacement and improvement on 520, according to the study, because increased congestion on other roads could push drivers back to the tolled road.

WSDOT officials said assumptions in the study, prepared by South Carolina-based Wilbur Smith Associates, are very conservative as the document is being used for revenue projections.

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Last December, when WSDOT was campaigning for the tolls, officials said peak traffic on I-90 could increase by as much as 9 percent, slowing down the average trip by five to 10 miles an hour. According to the study, 72 percent of the drivers surveyed say they would divert to I-90, while another 20 would use State Route 522.