Milepost 31 is an award-winning information center that highlights the people and projects that shaped Pioneer Square, and provides an inside look at the SR 99 Tunnel Project. There, you'll find more than just construction photos and brochures. You’ll find history, artifacts and interactive exhibits designed to broaden your understanding of the land beneath you. You’ll explore the neighborhood’s changing landscape, from earth-moving efforts of the past to the massive tunnel project that will soon move State Route 99 underground and reconnect Pioneer Square to the waterfront.
Location and hours
- 211 First Ave. S., Seattle
- Admission is free.
- 11 a.m. to 5 p.m. Tuesday - Saturday (closed on state holidays)
- The center will be closed on Sat, April 22
- Open until 8 p.m. on the first Thursday of each month during the Pioneer Square Art Walk - see below for details.
Visitors to Milepost 31 can browse through four sections:
You Are Here: Similar to the "you are here" points on maps, this section orients visitors to Milepost 31. It tells the story of the land upon which you are standing from the perspective for several different historical figures.
Moving Land: This section examines how the natural forces of glaciers, earthquakes and volcanoes have transformed Seattle's landscape during the past 20,000 years. Visitors will also learn about our own effects on the land, from the filling of the tidelands in Pioneer Square to the various regrade projects across the city.
Moving People: This section tracks transportation over time, with an emphasis on Pioneer Square. Visitors will see how people-moving has changed - and in some cases stayed the same.
Moving Forward: This section is all about tunneling. Visitors will learn about the history of tunneling technology, tunneling in Seattle and, of course, the SR 99 Tunnel Project. In addition, exhibits show visitors how the project - along with the Elliott Bay Seawall Replacement and Waterfront Seattle - will transform the future of Pioneer Square.
Why the name “Milepost 31”?
Mileposts mark progress. They help you track where you are on your journey, reminding you of the places you’ve passed through on your way to somewhere else.
But what if a milepost is so interesting that it becomes a destination? Located on SR 99 at the western edge of Pioneer Square, Milepost 31 is that kind of place. It marks a spot on the highway (milepost 31 on State Route 99), but it also marks the spot where, before mileposts existed, mile-thick glaciers gave way to native civilizations. It’s where Seattle’s first neighborhood saw the rise of the city’s most notorious stretch of highway - the SR 99 Alaskan Way Viaduct - and where crews building the world’s largest diameter bored tunnel to replace the viaduct will first cross into the soils beneath Pioneer Square.
One of the best ways to keep up with all the happenings at Milepost 31 is to join the Milepost 31 Meetup page.
First Thursday speaker series
WSDOT hosts a monthly speaker series in conjunction with the First Thursday Art Walk in Pioneer Square. Check back soon for information about the next event.
If you have questions about Milepost 31 please call the program hotline at 1-888-AWV-LINE, which is answered by staff between 8 a.m. and 5 p.m. on weekdays.