It is about that time of day when thousands of geeks hop in their cars and make the commute over the 520 floating bridge — the main artery connecting Seattle and Redmond. For those stuck in traffic — which can be particularly horrendous on days when the sun emerges after long spells of cloudy weather (like today) — the commute is one of the most dreaded parts of the day.

But here’s some news you probably don’t want to hear (or won’t believe) if you are about to get stuck in the 520 mess. An analysis by Clark Williams-Derry at the Sightline Institute finds that traffic patterns on the state route 520 bridge actually have declined in the past decade. (See chart below).

That shocked us, in part because Microsoft’s employment in the region has mushroomed during the same period Williams-Derry analyzed.

Microsoft, which is by far the biggest contributor to commuters on the 520 bridge, now employs 40,000 people in the Puget Sound region. (89,000 worldwide).

That means the company has added roughly 15,000 employees in the Seattle area alone in the past five years. Even more startling, if you look at the employment growth at Microsoft in the region since 1995, it has added a whopping 30,000 employees here.

Now, some of those workers may be telecommuting, living on the Eastside already or hopping on the Microsoft Connector bus service. But, I am guessing, a number of those workers are also driving in their cars over the floating bridge.

So, how has traffic actually declined given those employment gains?

That’s a good question, and we’ll probably need a transportation or statistics guru to help figure it out.

But Sightline’s Williams-Derry is using the analysis — along with what he says are some wild future traffic projections for the bridge from WSDOT — to shine a light on what he perceives as a wasted investment in a plan which is moving ahead to expand the 520 bridge to six lanes.

“It would be funny—if the state weren’t planning billions in new highway investments in greater Seattle, based largely on the perceived “need” to accommodate all the new traffic that the models are predicting will show up, any day now,” he writes.

Seattle Mayor Mike McGinn has continued to fight the 520 bridge project as well, and a blog post from the Mayor’s office today jumps on the numbers as well.

“Designing for thousands of cars per day that may not show up has resulted in a project with six lanes and a bigger footprint,” the Mayor’s office wrote. “A bigger footprint could cost us more money, more loss of wetland habitat, and cause bigger impacts to Seattle’s neighborhoods.”

They also point out that traffic across the bridge likely will drop once tolling begins, which is scheduled to happen this summer (but has been delayed on several occasions already).

Interestingly, Microsoft CEO Steve Ballmer spoke of the bridge project at Seattle Rotary late last month, noting that it was the type of progress the region needed in order to remain competitive.

Sightline Institute says traffic has declined on the 520 bridge in the past 15 years despite Microsoft adding 30,000 employees in the region.
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