Tacoma Narrows Bridge: It Is Happening Again

How is Washington's transportation budget like Twin Peaks?
This post is 43 in the series: Dude, Where Are My Cars?

For those of you old enough to remember Twin Peaks, I present my suggestion for the ideal spokesperson for the Washington State Transportation Revenue Forecast Council:

OK, now that the shivers have worn off, let me explain.

WSDOT depends on revenue from tolling to pay for some of its construction projects. One notable example is the Tacoma Narrows Bridge: WSDOT added a second, tolled span in 2007, counting on steady growth in traffic volumes to pay for the original construction costs.

Tacoma Narrows Bridge traffic: actual vs.forecastBut instead of rising steadily, as originally projected, traffic started tapering off. (See the red line to the right.) At first, transportation planners pinned the declines to the Great Recession of 2009. But after rebounding in 2010, traffic across the bridge has fallen slightly for three consecutive years—confounding policymakers, and forcing a series of controversial rate hikes.

Still, despite higher toll rates that appear to be discouraging additional traffic, state transportation forecasters are once again projecting a prompt increase in traffic—with annual growth rates increasing from 2 percent in 2015 to 4 percent in 2017, before tapering back down to around 1.5 percent in 2022.

So why the creepy Twin Peaks guy? Simple: the new forecasts essentially represent a return to the failed 2006 forecasts, which predicted endless growth in traffic that would quickly pay for the construction costs for the new span:

TNB traffic actual and 2 forecasts

The creepy Twin Peaks guy is perfectly correct: it is happening again. Without justification, state transportation officials are projecting a rapid increase in traffic volumes that they expect will help solve the problem of underfunded construction projects—despite the fact that there’s essentially no evidence that traffic will suddenly start growing the way it did back in the 1950s. If anything, the new forecast is even more preposterous than the old one, since it predicts faster growth in traffic than the 2006 forecast, despite clear evidence that traffic across the span is at a standstill, or perhaps declining.

The abject failure of “endless growth” traffic forecasts isn’t just an academic issue. It’s actually starting to wreak havoc on transportation budgets all across the Pacific Northwest. Unrealistic traffic growth forecasts pack a double whammy: transportation planners who rely on them feel obligated to accommodate all that new traffic by building massive highway megaprojects; but the failure of the traffic to appear means that there’s just not enough revenue to pay for the overbuilt roads, bridges, and tunnels.

That, in a nutshell, is at the heart of the region’s transportation budget “crisis.” We have built, and are still building, more high-cost road projects than we actually need, even as revenue from gas taxes and tolls just isn’t showing up to pay for it all.

520 Traffic Projections vs Reality

And another thing: to my eye, the Tacoma Narrows Bridge forecast looks very much like the beginning of the state’s bizarre predictions for traffic across the 520 bridge…which for years and years projected that traffic would start growing quickly, even as actual traffic levels stayed roughly flat. Yes indeedy, it is happening again.

Of course, it’s possible that the forecasts could turn out to be correct: even stopped clocks are right every so often. Still, by predicting endless traffic growth, state transportation officials are just making transportation budget woes worse. By forecasting rising revenue that’s unlikely to appear, the “endless growth” forecasts encourage a mentality of “build now, pay later.” For the public, that’s a risky gamble, since it means that future generations will have to keep paying for our bad infrastructure bets today.

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  1. Jack Whisner says:

    The law of demand cannot be repealed or ignored. It has been neglected before: WPPSS and nuclear power and deep bore tolling.

  2. Scott Walker says:

    I very much appreciate the work that Sightline and Clark are doing to change the discussion regarding transportation from car-centric to all modes. But besides the task of pointing out the massive mistakes of the DOT and who will pay, how does one get a handle on their throttle? The RTPO’s were supposed to have oversight, but since the DOT holds and controls the information and assists in agenda setting, that doesn’t work. Meanwhile, DOT continues to spend us into stranded investments while we need to spend into a different transportation future. I see no answer short of the governor stepping in with the bully pulpit. Any thoughts?

  3. Alan Locklear says:

    Planners used to be infamous for making forecasts that were nothing more than extrapolations of current trends. Now they appear to be ignoring current trends and simply pulling predictions out their –ahem– posteriors.

  4. Tim says:

    The same thing is happening north of the border.

    Port Mann: http://www.abbynews.com/news/116879748.html
    That’s based on a traffic forecast of 150,000 daily users paying tolls – 20 per cent more than the 125,000 who crossed for free in 2007 and about seven per cent more than the 140,000 the bridge is expected to carry this year.
    That break-even date, however, depends on the number of daily paying drivers climbing to between 175,000 and 180,000, and tolls exceeding $200 million. By 2021, the bridge is expected to carry 189,000 vehicles per day.

    Actual vehicle crossings have dropped from when the bridge was free and only 5 lanes wide now it is tolled and 8 lanes wide.

    The Golden Ears bridge is loosing $35-$45 million dollars a year. This is being taken away from Transit. http://bc.ctvnews.ca/golden-ears-bridge-losing-up-to-45m-annually-1.1474467

    Now the government wants to build a new 10 lane crossing for the replacement of the 4 lane George Massey Tunnel. http://www.cbc.ca/news/canada/british-columbia/bridge-to-replace-george-massey-tunnel-says-premier-1.1862247

    The highway builders are going gangbusters over here!

  5. Mud Baby says:

    In the past, Seattle Public Utilities has done the same face plant with respect to projecting future water demand, as shown here (scroll down to Figure 1):


    The fact that SPU’s ratepayers are much better at conserving than SPU is at forecasting may be a sign that the people who run SPU have drunk the “endless growth” Kool-aid.

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