Morning commuters traveling south on I-5 will face a traffic jam that lasts an hour longer if a new, wider 520 bridge is built according to prevailing plans, says the Washington State Department of Transportation (WSDOT). The backup would extend roughly from the ship-canal bridge (where the two freeways intersect) to the Convention Center (where the express lanes end), officials say.

To be clear, the travel times during peak congestion would not necessarily be longer, says WSDOT engineer Michael Horntvedt, but rather the morning traffic jam's duration would extend for an additional hour.

This ramp replaces one of the freeway lanes
  • This ramp replaces one of the freeway lanes
The problems result from a ramp off of 520 that would empty onto southbound I-5 (onto the express lane that connects to the mainline further south). “This would increase traffic pressure to an already congested lane," says a white paper from a workgroup created by the legislature. By 2030, "Congestion could last up to an hour longer compared to the No Build alternative and extend just north of the SR 520 interchange at the peak."

The proposal would also eliminate one of the express lanes on I-5 across the ship canal from four to three (more on that below). Meanwhile, 520 would widen from four lanes to six.

Fran Conley, director of the Sustainable 520 Coalition, blasts the proposal. “It means that there is no net gain to this proposed design because—even if it helps people from the eastside—it will harm people going north and south, so from a public policy point of view, you will have spent billions of dollars for no results,” she says.

But state officials say that whatever delay is caused in southbound traffic, the new bridge makes up for by expediting traffic in other directions. Most significant, according to WSDOT engineer Horntvedt, the wider 520 bridge will allow more cars to get off of I-5 when they are attempting to go east (using 520). "We see substantial benefit for people traveling the northbound to eastbound direction," he says. "So you have to take in the whole picture."

Click for larger image: One less express lane over the ship-canal bridge
  • Click for larger image: One less express lane over the ship-canal bridge
The underlying problem with the new bridge, critics argue, is that the new 520 bridge would increase from four lanes to six lanes (rebuilding a four-lane bridge would not have the same impacts on I-5). As a result, more traffic would also exit onto city streets.

"The I-5, 520 choke point is one of the worst in the region," says Mayor Mike McGinn. "The problem isn’t 520's increased capacity—it’s the [unchanging] capacity of I-5 and the surface streets, which is why focusing on transit is much more efficient use of our resources."

WSDOT says that the wider bridge also allows the state to connect HOV and transit lanes from I-5 all the way east to Medina.

Conley, however, still doubts that the trade-off is a good deal, saying that "the project is poorly designed and will not accomplish what anybody wants for it. The state doesn’t have the money for it, but is going to be raising taxes and tolls trying to get more money for it. It will do much more harm than good." She also points to the disappearance of an express lane on I-5.

“The design would reduce the number of lanes from four to three in the express lanes across the Ship Canal Bridge to provide space for a single new HOV/transit ramp to/from SR 520,” the report says. The problems stem from the interchange of I-5 and SR 520. In the new arrangement, a lane would connect 520 to the reversible express lanes on I-5, thereby consuming one of the four lanes across the ship-canal bridge.

Estimated to cost $4.65 billion, the project still lacks financing for approximately half that amount, despite plans to begin tolling the bridge (which officials say could sink in adverse weather or an earthquake) this spring.

"I don’t think the public is fully aware of the significant issues with the project right now," says McGinn. "This is something we need to fully air and discuss because proceeding with a project that we're a couple billion short of completing, and if completed, if we ever get the money, would have unacceptable impacts to Seattle."

WSDOT officials plan to release the full findings of their research in a Final Environmental Impact Statement in June.

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