West Seattle Link and Climate Change

Recent Hurricane Helene and numerous other weather events around the world have reinvigorated the discussion on how to slow down the climate change related to carbon emissions. Transportation is the largest contributor to those emissions, so many efforts focus on it, in particular to reduce individual car usage. Many transit advocates push for more transit infrastructure investments to make it more attractive to switch from individual car use to transit with its associated lower emissions. This was one of the primary goals of ST3, too. Of course, the initial construction of such infrastructure also generates emissions which need to be considered. I reviewed the recently published West Seattle Link Extension Environmental Impact Statement (EIS), as well as the prior Draft (DEIS), and contacted the Puget Sound Clean Air Agency to learn about the trade-offs. Unfortunately, the current preferred alignment will not help the region.

Of course, any infrastructure investment will have some environmental impact. The EIS is supposed to look at various options, including sticking with the status quo (No Build") to see what option has the greatest benefit for the community. This is also referred to as a Life-Cycle Analysis (LCA). With sufficient ridership rail investments (urban or even HSR) usually come out ahead in studies. TransLink (Vancouver, BC) did a full life-cycle analysis for example as part of their business case to improve serving the Burnaby Fraser University campus. (It compared various transit modes and determined that a gondola would be better for this line than other modes currently used in Vancouver.)

The Executive Summary of the WSLE EIS states: The West Seattle Link Extension is expected to reduce dependency on single-occupancy vehicles, slow down growth in vehicle miles traveled, conserve energy, and reduce greenhouse gas emissions. The project is anticipated to reduce daily vehicle miles traveled by approximately 17,000 by 2042, helping to achieve Washington state's greenhouse gas emissions goals. " While the summary talks about the positive impacts, it misleads the public by not even mentioning any adverse carbon impacts from its construction. I had to dig deeper. (my earlier post did a similar analysis for the DEIS)

Car Trips and Carbon Reduction

To estimate the positive impacts of new transit options, the EIS looks at the reduction of vehicle miles traveled (VMT).

WSBLE DEIS West Seattle bridge traffic impact analysis

The DEIS forecasted a reduction of 400 car trips (less than 1%) on the West Seattle bridge every morning (700 in the afternoon) and only provided an estimate of the combined trip reduction of both the Ballard and West Seattle lines. In the EIS they dropped the bridge forecast and only provided an estimate of the daily trips and VMT overall. They did not provide any background on how they reached those estimates. They did mention that if only the Minimum Operable Segment (MOS) from SODO to Delridge would get built, it would not provide quite as much reduction but not as much adverse impact either (it would not include a tunnel).

EIS Vehicle Miles Travel and Daily Trip Reduction

While the table shows a reduction of 15,400 miles per day (about 0.02%), the Executive Summary states a reduction of 17,000 miles once the line connects downtown. I assume they also added the reduction of transit bus miles even though Sound Transit promises that KCMetro will reallocate bus hours to serve more West Seattle neighborhoods.

The EIS then applied the FTA Greenhouse Gas (GHG) Estimator v3 to estimate an annual carbon reduction of 3000 metric tons.

Construction-related Carbon Emissions

The EIS then proceeds to estimate the construction-related carbon emissions including embodied emissions from the production and transport of fuel and materials". Even though the FTA warns that the tool only provides a resource to generate coarse but informative estimates of GHG emissions", in an appendix the EIS compares the carbon reductions with the initial construction related carbon generation.

While the DEIS estimated construction would generate between 158,067 (no tunnel) and 614,461 tons (long tunnel), the EIS now estimates it between 80,508 (50% less) and 509,544 tons (20% less, or even only 206,723 tons if they further discount tunneling related carbon emissions).

For the preferred alignment they estimate now 380,181 tons (or 140,952 tons using the same discount). When they estimate energy consumption, they explain the different classifications between the three estimates (low-cost, high-cost, preferred) in more detail:

As the FTA pointed out, such models are very coarse, they are based on number of stations and miles of either at-grade, elevated, or tunneled. It does not take into account that most of the elevated guideway in the WSLE is more than 100 feet high, far higher and complicated than most elevated rail projects, and includes a 200+ feet bridge over the Duwamish. What the EIS classifies as at-grade" is mostly a trench along Fauntleroy Way and a heavily fortified cut through Pigeon Point with extensive retaining walls, this is not what usual at-grade alignments (such as along I-5 toward Federal Way) typically look like. While an at-grade station such as Stadium Station requires little construction, this is not the case for either the SODO or the Avalon stations. The SODO station is a 4-track transfer station with a mezzanine. The mezzanine allows access from S Lander St and crossing of multiple tracks. The Avalon Station is almost a tunnel station as it is mostly underground with just a few ventilation openings. I would estimate that the preferred alignment would be a lot closer to the High Cost alternative or even higher, because even the High Cost alternative does not consider any such complications. Now that a lot of the details of the stations and route have become available, I had expected that the EIS would have included detailed carbon emissions calculations based on the specific materials and construction efforts in the WSLE project rather than the rough estimates it provides. Rough estimates may be sufficient for generic alignments such as along I-5, but soil conditions, environment, construction complexities, and topography of this project are far more complex. Rough estimation will most likely underestimate the actual carbon emissions.

Net Benefit

Finally, in Appendix L4.6E1 (242-page file!) of the EIS, the annual carbon impact is determined by comparing the annual carbon reduction with the construction-related carbon emissions. The construction related emissions are amortized over the expected 50-year life span of the project.

EIS Appendix L 4.6 E1 determining overall annual carbon emissions

If the rough estimate is accurate, an elevated alignment may have some net positive impact by slightly reducing carbon emissions over the life of the project. For the preferred as well as any other tunnel alignments the VMT reductions will never be able to offset the construction related carbon emissions. Instead, the WSLE will contribute up to 362,750 tons of carbon to the pollution in our region. Most of the carbon will be generated during concrete and steel manufacturing and associated truck traffic, both of which will happen right along the Duwamish River. This area is already the most disadvantaged area of our city, known for its superfund cleanup site, high air pollution and noise levels.

Clean Air Agency Response

When the Puget Sound Clean Air Agency about the carbon footprint of the WSLE project, I received the following response (bold emphasis added):

The intent is to reduce transportation emissions for all overburdened communities, including those located in the Duwamish Valley. I encourage you to look at our overburdened communities map that highlights our communities that facea combination of poorer health outcomes, more air pollution sources, and whose residents face socio-economic barriers to participation in clean air decisions and solutions. It's no coincidence that many of these communities follow the I-5 corridor. Reducing transportation emissions hits all three components of our mission (air quality, climate, environmental justice) because transportation emissions are a major risk driver for all three (the links in the email below highlight this). Of course, zero emission vehicles will be a major component to reduce transportation emissions, but mode shift (including light rail) also has an important role to play. Construction impact is small and temporary (and can be minimized with intentional use of cleaner equipment) compared to the long-term regional gains transit projects yield. This is particularly important for our near-roadway overburdened communities."

Kathy Strange, Air Quality Programs Director

As a follow-up, I pointed out that all of Seattle's transportation related annual carbon emissions are 1.8 million tons. I do not consider carbon emissions of several hundred thousand tons small" when the city's stated target is to become pollution free by 2030. I also explained that the WSLE will not serve these overburdened communities directly. Many riders from those communities will have to do extra transfers which will increase travel time and complexity. Nevertheless, these communities will be most impacted by the construction-related truck traffic and emissions (both carbon and particulate). I did not get a response.

Conclusion

Sound Transit's System Expansion Committee will meet on Thursday (October 10) to discuss the final West Seattle alignment. Will they agree with the Clean Air Agency that construction-related carbon emissions are negligible? I hope they take those emissions into account by either putting the WSLE on hold or at least by choosing an elevated alignment.