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Bertha tunnel machine
Bertha, the Seattle tunnel machine, completed its boring operations beneath the city with breakthrough on April 4. The tunnel won’t open to traffic until 2019. (Flickr Photo / WSDOT)

Seattle’s new Alaskan Way tunnel — currently three years late and millions of dollars over budget — has been called the worst transportation investment in the entire United States. Now, like nearly every construction project in the city, people are hitching its fortunes to tech workers.

According to a recent study commissioned by the Washington State Department of Transportation, thousands of vehicles will divert onto other roads when the tunnel replaces the Alaskan Way Viaduct in 2019. This is due to its lack of downtown exits and its tolls, which are needed to raise the $200 million mandated by state legislature.

Seattle traffic
Snarled traffic in Seattle’s South Lake Union neighborhood. (GeekWire Photo / Kevin Lisota)

The task for planners is to set tolls high enough to cover its bills, then find enough people willing to pay them every day. So who will these tunnel commuters be? Tech workers, the theory goes, since the northern exit will be in the South Lake Union area. A recent column by the Danny Westneat of The Seattle Times, for example, argues that the neighborhood’s rapid development helps the tunnel make “more sense.”

“Seriously, West Seattleites who derided this tunnel all those years,” he writes. “If you now work at Amazon, as increasingly many of you do, somehow this boondoggle with no exits has morphed into a direct stoplight-free track to your offices.”

Some numbers back up this optimism. A recent Zillow study found that 53 percent of workers in South Lake Union live outside the city. A 2014 study by EMC Research found that nearly half of SLU’s workers drive to work alone. And Expedia, Facebook, and other firms are rapidly expanding their presence north of downtown, near the new tunnel’s exits.

But will commuters from South Lake Union’s tech scene really foot the tunnel’s bill? Here are three numbers that suggest not.

30,000 vehicles

That’s roughly the number of vehicles that the state Route 520 bridge across Lake Washington has lost in daily traffic, compared to when it wasn’t tolled. That’s about a 30 percent drop since late 2011, which may not sound so bad, until one compares it to the region’s stratospheric growth during this period.

When tolls were being considered for the floating bridge, tech workers were part of the equation. After all, it offers the most direct route from Seattle to Microsoft’s headquarters in Redmond, Wash., Google’s growing campus in Kirkland, and a range of other successful companies outside Seattle.

Even with that well-paid clientele, planners needed to prepare for a major drop in traffic after tolls. The idea of underused Seattle highways can seem strange to some, given the seemingly constant gridlock. Nonetheless, traffic volumes on the floating bridge plummeted when tolls arrived in 2011, and have only improved slightly since then.

(Above: Average daily traffic volumes on Highway 520.)

Since tolls were enacted, Microsoft has added about 5,000 Puget Sound employees, while Google doubled the size of its Kirkland outpost. Seattle is currently the fastest growing city in the U.S., and has ranked in the top five for years. Both it and surrounding towns are among the nation’s most competitive real estate markets.

Yet traffic on 520 remains far from its pre-tolling peaks. Looking at the data, Washington State Department of Transportation spokesperson Ethan Bergerson told me some commuters have been diverted to other routes by 520’s tolling. But other vehicles, he said, have disappeared off the grid entirely.

Where did these drivers go? Many simply turned into passengers.

70 stops

That’s the number of pick-up and drop-off locations for Microsoft’s private Connector bus system, with routes running throughout the day all over the county. Shuttles include Wi-Fi, plush seats, tray tables and power outlets, so staffers can get to work before they get to work.

When tolling began on the floating bridge, Microsoft responded by expanding its Connector service, which started a decade ago with only a dozen buses capable of transporting 1,500 staffers. The fleet is now capable of carrying more than 7,000 employees.

Microsoft Connector
Microsoft’s Connector bus system is capable of carrying 7,000 employees.

In the Bay Area, companies such as Google, Yahoo, Facebook and Apple have offered these sorts of shuttles for a long time, in addition to free public transit passes for employees. The trend is spreading to Seattle. Amazon launched a bus service last October, and Expedia is planning private shuttles for staff at its new Seattle headquarters. It’s not hard to imagine Facebook and other companies following suit.

These buses will remove cars from the road and may improve gridlock slightly. But no one riding them will be helping with the cost of the Highway 99 tunnel.

20 percent

That’s the proportion of Amazon’s roughly 25,000 Seattle employees who walk to work, according to the company. In addition, less than 50 percent of employees commute by car, and 15 percent live in the same zip code as the company.

In his column, Westneat notes that the tunnel’s exit “dumps into the heart of one of the fastest-growing job markets in the nation. Right now there are 22 skyscrapers of 40 stories planned for development within 10 blocks of the tunnel’s exit.”

That may not be such a good thing. The financial bet behind all those residential towers is that tech workers are often younger, and prefer to live in walkable urban communities, not far-flung suburbs from which they drive every day. The more tech workers who live near their companies, the fewer of them who need a tunnel through which to commute.

(Above: In-progress residential developments in South Lake Union, with dot size indicating number of units. Data courtesy of Seattle in Progress.)

The influx of young people to Seattle is why, between 2010 and 2015, the level of car ownership in the city dropped for the first time since the 1970s. Not only that, ownership dropped faster for millennials in Seattle than in any other large U.S. city. The growing local tech scene, and the rise of walkable neighborhoods, are big parts of that.

It’s true that there are a lot of parking spots attached to those new residential developments in South Lake Union. However, WSDOT spokespeople and Clark Williams-Derry, a traffic expert with progressive research firm Sightline Institute, both noted to me that there’s only so many vehicles a road can actually hold. Eventually it gets full. And that’s already happening in South Lake Union, before those high rises open.

As rush hour in Seattle goes from terrible to nightmarish in coming years, and the city becomes denser, there’s no reason to think a much higher number of South Lake Union’s workers will choose to commute from south of downtown. Williams-Derry said these arguments are symptomatic of an outdated understanding of traffic.

“There’s a difference between traffic volumes and congestion,” Williams-Derry said. “Congested roadways don’t carry many cars. The traffic volume goes down. It all jams up. … If rush hour gets bad enough, people move, or take a bus sometimes. On congested urban freeways, traffic hits equilibrium.”

Ever since it was proposed, people have struggled to explain how a multi-billion dollar tunnel beneath the city, with no downtown exits, makes financial sense. The tech workers in Seattle’s emerging “second downtown” probably won’t make that any easier.

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