Environmental Impact of Transit Projects such as the West Seattle Link Extension
One of the FTA's stated goals is to help metropolitan areas meet national ambient air quality standards (NAAQS) by reducing overall vehicle emissions and the pollutants that create smog" and to reduce fuel use and greenhouse gas emissions." So we just need to build more transit, right? But what about construction-related emissions? The recent Seattle Transportation Plan (p. 188 3-98) draft states that, Given the transient nature of construction-related emissions and regulatory improvements scheduled to be phased in, construction-related emissions associated with all alternatives would be considered only a minor adverse air quality effect." However, Sound Transit's draft Environmental Impact Statement (DEIS) estimates that the West Seattle Link extension (WSLE) will generate 614,461 tons of carbon. As so often the answer is: It depends!
I certainly share Seattle's hope that recent regulatory changes encourage or even mandate the use of less carbon-intensive construction materials and machinery, but realistically that transition will not happen overnight. Construction companies won't scrap all their machines and purchase new ones. McKinsey estimates that cement production will only reach 30% of the carbon-emissions reduction required to meet the 1.5-degree Celsius goal. Therefore, I don't think we can just ignore the construction impact but take it into consideration. I don't accept Sound Transit's assertion that short-term greenhouse gas emissions during the construction ... would be temporary" either. Emissions have an immediate impact to the health of residents and our climate; they tend to stick around for a while. How about their assertion that they will be offset by the emission reduction during project operation, well within the project's life span, due to the reduction of regional vehicle miles travel"?
For West Seattle, Sound Transit is proposing elevated and partially underground light rail. The DEIS estimates that constructions will generate 614,461 tons of carbon based on typical averages for elevated and tunneled rail projects. As the WSLE guide rail is much taller than typical elevated light rail lines, the actual carbon emissions are most likely even higher. (For comparison Seattle's total annual transportation needs generated 1,887,000 tons of carbon in 2020.) As KUOW already pointed out before the ST3 measure passed, most of these emissions would be generated at Ash Grove Cement in Georgetown, a marginalized community which already has one of the highest pollution levels in Seattle.
When the WSLE is finished it will only run to SODO and riders will need to transfer to the 1 Line. Like the East Link Starter line, during that time Sound Transit does not expect much ridership. Once the downtown connection is finished, Sound Transit estimates that during peak 100 riders will switch from driving a car across the bridge to using the train for a total of 400 riders daily by 2042. The EPA estimates that each traditional car emits 4.6 tons of carbon per year. If these 400 car owners would sell their car and always use transit, then it may save up to 1840 tons of carbon a year. If we take the construction-related carbon into consideration it may take 334 years before this project would generate a net positive outcome, even longer if some of these vehicle owners had already switched to an EV. In any case this will be beyond the life expectancy of this infrastructure.
Should we just all buy electric vehicles (EV) and forget about transit? There are a few small EVs starting at $25,000, but regular ones sell for well more than $40,000, used EVs are not much cheaper, and their batteries are not as good. For many people this isn't even an option.
Even if you are able to afford and operate an EV, any car, electric or not, needs road construction and maintenance and requires lots of road and parking space. EV's batteries require mining for rare metals around the world and even if we can switch to green energy production the heavier EVs still generate toxic emissions from lubricants, tires and brakes, some of these even more than traditional cars due to their extra weight.
What about other transit modes? If we can use our existing road network to run buses then we may not need to build new infrastructure, painting existing lines red for bus lanes is relatively easy. For most of our RapidRide lines we still rebuilt the roads. If we can make those lines faster it may convince more people to leave their cars at home, then that may still be a net benefit. Trolley or battery buses can use green energy though they still have similar issues as EVs have, but much less per rider. Even current diesel buses emit far lower emissions than individual vehicles per rider. Increasing bus frequency and coverage is far more important than replacing diesel buses before the end of their life with electric ones.
Rail projects are not generally bad for our environment. West Seattle has many hills, other transit modes such as buses or a gondola line would handle that much better, but a rail line will need to get over or around the hills as rail can't handle gradients well. Flat at-grade rail lines have the least carbon impact. Elevated lines are slightly higher. Tunneled lines and stations have the highest carbon impact. Automated rail tends to use shorter trains which reduce station size and carbon impact. WSLE's carbon impact increased considerably when the preferred alternative was changed from elevated to underground. Not only will this increase the carbon footprint for this project, but also increase the carbon impact of any future extension as the line will have to continue in a tunnel until it can surface again. While tunneling may be required to gain the support of downtown businesses to serve high ridership stations in downtown Seattle, Sound Transit only expects 400 additional daily riders for the WSLE - not enough to warrant the environmental impact.
To meet Seattle's climate goals, the city needs to work with our transit agencies to reduce vehicle miles traveled (VMT) by increasing transit ridership. Enticing car owners to switch modes may require new infrastructure, but the carbon impact of any construction needs to be balanced with the VMT reduction. In some cases rail may be justified, but in other cases increasing bus services or other transit modes with a lower carbon footprint such as gondola technology may provide a greater net carbon reduction.