Location: Seattle, WA

There’s a lesson to learn from Proposition 1’s failure, one that might be less obvious: climate protection and transportation are inextricably linked. Much of the Proposition 1 debate centered on the package’s climate implications for a state that has committed to reduce greenhouse gas emissions to 50 percent below 1990 levels by 2050, and where many cities, including Seattle, have been national leaders.

The opposition argued global warming. So did the measure’s supporters. When Ron Sims withdrew his support, he cited the climate-warming emissions from added traffic as one of his chief objections—he was thinking about his granddaughters, he said, not just the next five years.

“Puget Sound voters are reluctant to expand roads because they lock us into decades of increased climate pollution,” says Eric de Place, Sightline senior researcher. “Driving is already responsible for one-third of Washington’s emissions, so future transportation packages should account for the climate impacts.”

As Puget Sound residents take responsibility for climate protection more seriously, future transportation packages will need to address climate change as a guiding principle. Transportation projects that embrace climate protection should:

  • Stay ahead of the curve by estimating the climate impacts in advance.Emissions estimates should be calculated for every large transportation project. Greenhouse gas accounting is still a new field, so analysts may at first be able to obtain only ballpark figures for the expected emissions from some new projects. But reasonable estimates are still useful. And many aspects of climate accounting are fairly straightforward: we already forecast how many cars a new highway will carry, so why not estimate how much gas those cars will burn?

    Sightline developed a general estimate showing that in congested urban areas a single new lane mile of road adds at least 100,000 tons of greenhouse gases over 50 years. Detailed analyses of direct impacts, especially tailored for local areas, can help planners and voters determine the most responsible solutions for the region.

  • Consider transportation projects an opportunity to improve land use patternsOur transportation choices and land use patterns are closely intertwined. Adding new highways can induce low-density sprawl, which in turn lengthens trip distances and requires car travel for nearly all trips. New roads can tilt development patterns toward car-dependent sprawl for decades to come.

    Planners should begin to examine the greenhouse gas impacts of building and operating a light rail, implementing HOV/HOT lanes, or fostering compact development near transit. In addition, we should study how adding lanes on the urban fringe may lead to new low-density development and increased emissions.

Proposition 1 may have been the last of a dying breed: a transportation package, presented to the voters without a clear accounting of climate impact.

“Transportation is the most important piece of Washington’s climate change puzzle,” states Sightline senior researcher Eric de Place, “Analyzing the impacts of our transportation projects can create real opportunities to move climate protection in the right direction.”


Sightline Institute is a non-profit research and communications center based in Seattle. You can find our report on emissions and transporation projects here: Widening Roads: Short-term Traffic Relief, Long-term Emissions Increase.

November 7, 2007