The advocacy group Seattle Subway suggests it’s time to start thinking ST4, three years after voters passed ST3. Here’s the map of possibilities they’re circulating:

Again, this is a volunteer group, not formally affiliated with Sound Transit or any other government agecy, but the prospect of where light rail goes next has been raised many times as the West Seattle extension is planned, so we’re publishing their pitch:

In 2016 Seattle took a bold step toward carbon-neutrality by voting to expand the Link rail system—acting in the face of a climate crisis that chokes our blue summer skies with wildfire smoke, combined with a growing influx of new residents to our city.

Planning and building rail extensions takes decades, however, and a completed ST3 system will still leave frustrating gaps in Seattle’s densest neighborhoods, like Belltown and First Hill. That is why we must start working on ST4 now to expand Link service and move toward a vision of Seattle that is fully connected by high-quality transit.

Our next rail expansion vote on ST4 should come in 2024. More people than ever will be riding Link in 2024 as major stations open in Northgate, Bellevue, Redmond, Federal Way, and Lynnwood. Critically, we will still have a window to design major ST3 stations and infrastructure for transfers and future expansion, since they must be planned that way from the start. The only way to avoid short-changing the potential of our investments in ST3, including a brand-new downtown subway tunnel, is to plan ahead with a Seattle-focused ST4 plan.

“Seattle is growing fast and started out decades behind on rapid transit,” said Keith Kyle, executive director of Seattle Subway. “When projects can take dozens of years to deliver, we don’t have time to wait around on getting started. We need to leverage the investments we’re already making to create a true Seattle Subway.”

Seattle residents should have the option to catch a train in Georgetown, Wallingford, or White Center and enjoy a smooth ride to Lake City, Crown Hill, or Fremont. We live in one of the most beautiful cities on the planet but spend far too much time stuck in bumper-to-bumper traffic, spewing carbon emissions from our vehicles.

“Improving Seattle’s public transit system serves everyone,” said Seattle Subway political director Ken Anderson. “Growing our Link network brings environmental, economic, mobility, and quality of life benefits to every person who doesn’t drive or is sick of wasting their time stuck in gridlocked traffic.”

To pay for this expansion, we have identified two existing funding sources with strong potential: The City Transportation Authority (CTA) and the Seattle Transit Benefit District (TBD). The CTA can be used in its current form, but can be greatly improved with state action. Please join us in urging your state legislators to improve the CTA.

“Seattle residents have a chance to make an impact on national and global issues like inequality and climate change by voting locally to expand transit access,” said Kjersti Egerdahl, board member of Seattle Subway. “Seattle can show leadership by developing a strong ST4 ballot measure.”

To make this vision of ST4 a reality, Seattle Subway is working alongside a coalition of partners to build grassroots support, talking to local elected officials, lobbying for small changes in state law, and preparing to run a ballot measure in 2024.

“The more stations Sound Transit builds, the more Seattle votes with our feet,” said Ben Broesamle of Seattle Subway’s Board of Directors. “As we continue to build today, we need to stay focused on the future and create more connections for everyone in the region.”

We stand at a crossroads to determine the future of rapid, low-carbon transit in Seattle and across the region. If you share our goal for transportation progress, come join Seattle Subway. Help us write our upcoming series explaining why each new ST4 line needs to be built. Help us connect with people at farmers markets and community events around Seattle to grow this movement. Help us by calling, emailing, and writing your elected representatives and Sound Transit officials to let them know you want more rail expansion.

Traffic is over, if you want it. Today, we invite you to join the ST4 movement— for the environment, for generations of Seattleites to come, and for yourself.

Seattle Subway is an all-volunteer nonprofit advocating for high quality rapid transit.

Just in case you haven’t been paying attention – ST3, approved by voters in the three-county Sound Transit district, includes extending light rail to the West Seattle Junction, opening in 2030. The planning process has moved into the environmental-studies phase, with a draft Environmental Impact Report due out for public comment late next year.