Jump In Traffic Volumes Points To An Uphill Climb To Reduce Emissions

Photo by Ryan Packer.

Seattle’s average daily vehicle volumes increased by the largest amount in more than a decade in 2018, the most recent year of data available. The annual traffic report just released by the Seattle Department of Transportation (SDOT) counted more than 36,000 additional vehicles on Seattle’s streets per day, on average, compared to 2017–an increase of 3.6%. This outpaced the population growth for that year, which was 2.3%, for the first time in the past decade. Transit ridership growth for 2018 was also lower and well below the increase in traffic volume, as was revealed last month when King County Metro released its 2018 numbers.

Total average daily traffic in Seattle increased by 3.6% between 2017 and 2018, to 1,037,116 average daily vehicles (City of Seattle)
Total average daily traffic in Seattle increased by 3.6% between 2017 and 2018, to 1,037,116 average daily vehicles. (City of Seattle)

Stepping back, the latest numbers show that at last count the volume of cars on Seattle’s streets is pretty much exactly where it has been for most of the last decade. Which is remarkable considering the growth that the city has seen in its population and employment over the same timeframe. Seattle over the last decade added people and jobs without an associated jump in traffic volumes.

More people are biking than ever; fewer people are driving alone to their jobs downtown than ever. Our investments are doing what they are supposed to be doing. And yet more people are driving on Seattle’s streets citywide than ever, too. And that doesn’t bode well for meeting the City’s adopted goals.

Seattle’s Climate Action Plan, adopted in 2013, set a reduction target for passenger vehicle emissions based on 2008 levels: an 82% reduction. At the time this was passed, Seattle only needed to reduce emissions by 7.5% per year to hit the target by 2030.

Climate action plan goals for 2030 call for a 82% reduction in passenger vehicle emissions. (City of Seattle)
Climate action plan goals for 2030 call for a 82% reduction in passenger vehicle emissions. (City of Seattle)

Eight years later in 2016, Seattle had only reduced passenger vehicle emissions by just under 2% total, or 0.2% per year. That means that the yearly target after 2016 needed to increase to 11.4%, an even steeper goal.

While we are still waiting on the latest carbon inventory numbers, these 2018 vehicle volumes suggest that at best we are plateauing, and may even have erased some of that earlier reduction in emissions, given the spike in traffic volumes.

Since 2008, total vehicle miles travelled has been on a steady increase, with slight improvements in fuel efficiency keeping those emissions flat. But Seattle is not seeing an electric vehicle adoption rate anywhere near enough to make a dent. There were 6,700 electric vehicles on Seattle’s streets at the beginning of last year—around 2% of total passenger vehicles.

At this point, it would be hard to call any change from the status quo that is currently prioritizing personal vehicles on our streets too drastic. But that’s only if we take our commitments to combating climate change seriously. Last year, Mayor Jenny Durkan tweeted, “Our city doesn’t have the luxury of entertaining climate change denial.” This target should be easier than other emissions reductions, and we have no time to spare.

We hope you loved this article. If so, please consider subscribing or donating. The Urbanist is a 501(c)(4) nonprofit that depends on donations from readers like you.

Ryan Packer lives in the Summit Slope neighborhood of Capitol Hill and has been writing for the blog since 2015. They report on multimodal transportation issues, #VisionZero, preservation, and local politics. They believe in using Seattle's history to help attain the vibrant, diverse city that we all wish to inhabit. In December 2020, Ryan started a three-month stint as editor of Seattle Bike Blog.

Inline Feedbacks
View all comments
Miranda Marti

I am a Seattleite who gave up single car commuting last year, and it took a multi year career change for me to be able to do it. I have no regrets, but I still vividly remember a sinking feeling I had while reading an article about cruise ship fuel. After thinking of how hard I worked to change my carbon footprint, it really hit home to learn that one cruise ship running its engine for one day basically wipes out the everyday efforts of hundreds, if not thousands, of people trying to mitigate the climate crisis. I worry that carbon emissions from increased cruise traffic at the Port of Seattle could undermine efforts and interest in addressing the climate crisis on the municipal level.


Been working (and bussing) into downtown Seattle for 25+ years. Getting around this region is a “pick your poison” proposition. Some can swallow the limitations of public tranportation, choosing mental freedom over physical. Others would rather suck up the time behind the wheel, preferring the mental trap of focus on traffic while enjoying some physical freedom (can control temps, can pull off for a stop if needed). I am not sure you can change that second group: giving up your preferred control is tough.

Here’s an idea for an article: why don’t you do a survey of large downtown employers and publish a list of employers still subsidizing downtown parking for its employees? I’ve been working for downtown law firms for decades and they are the worst: nearly every attorney that works downtown drives due to $200 a month parking subsidy from the firm. Clogging up the roads simply to sit in their office all day – really this needs to be looked into. How many white-collar professionals have cheap parking downtown courtesey of their employer?

Grace N

Singularly, the most impactful thing Seattle can do to curb emissions is to ban or to enact strict laws to curb cruise ship emissions. Research shows one cruise ship idling for one day has the equivalent emissions to one million cars idling for one day (source: German research group NABU). In 2019, Seattle had over 200 cruise ships berth in our city.