Know before you go: the SR 99 tunnel’s new ramp intersections

Posted on Feb 3 2019 1:53 PM

The Feb. 4 opening of the SR 99 tunnel brings big changes to several important intersections at the tunnel’s north and south ends. New intersections can be confusing, so use the renderings below to help familiarize yourself with what you will encounter on the road. You can also preview the intersections via narrated videos.

North end of the tunnel: Harrison Street and Aurora Ave North

What’s changing:

  • New northbound SR 99 on-ramp
  • New southbound SR 99 off-ramp
  • Harrison Street open east-west across Aurora Avenue North

The new tunnel dives underground at Harrison Street, several blocks north of where the now-closed Battery Street Tunnel begins. The new intersection of Harrison Street and Aurora Avenue North is where the northbound on-ramp begins, and the southbound off-ramp ends. Harrison Street  is now also open east-west across Aurora Avenue North.

Rendering of Harrison and Aurora intersection

Note: Construction begins this month on the inside lanes of Aurora Avenue North between Denny Way and Harrison Street (yellow zone at bottom). Learn more about how the North Surface Streets project is rebuilding Aurora Avenue North.

North end of the tunnel: Republican Street and Dexter Avenue North

What’s changing

  • New northbound SR 99 off-ramp

The intersection of Republican Street and Dexter Avenue North is where the northbound SR 99 off-ramp ends. New signals will control traffic coming off the highway. From the off-ramp drivers will be able to turn left toward Mercer Street, head straight toward South Lake Union, or turn right to head toward Denny Way. Stay alert for people using the Dexter Avenue bike lanes on both sides of the street.

Dexter and Republican intersection rendering

South end of the tunnel: Alaskan Way, South Dearborn Street, and First Avenue South

What’s changing:

  • New southbound SR 99 on-ramp
  • New northbound SR 99 off-ramp [NOT YET OPEN]
  • New east-west street, South Dearborn Street
  • New primary path between First Avenue South and Alaskan Way
  • Alaskan Way extended farther south

One of the biggest changes to surface streets is at the tunnel’s south end, just west of CenturyLink field. Alaskan Way no longer ends with a jog under the viaduct onto Railroad Way South. Instead, it continues straight to a new intersection with a new road, South Dearborn Street.

South Dearborn Street is the new east-west connection between Alaskan Way and First Avenue South. This intersection connects SR 99, Alaskan Way and First Avenue. Alaskan Way continues south from this intersection toward East Marginal Way South. Railroad Way South is currently closed from First Avenue South, and when it reopens it will be a local-access-only road.

IMPORTANT NOTE: The northbound SR 99 off-ramp bridge is still under construction and will open one to two weeks after the tunnel opens.

Dearborn and Alaskan intersection rendering

Note: The rendering above does not show the now-closed Alaskan Way Viaduct, which sits in the yellow-highlighted work zone and will be removed section by section over the next six months.

South end of the tunnel: South Royal Brougham Way and First Avenue South

What’s changing:

  • New northbound SR 99 on-ramp
  • New southbound SR 99 off-ramp
  • Colorado Avenue South with two-way traffic to South Atlantic Street

Drivers who previously joined SR 99 northbound from Royal Brougham Way will find striking changes to that intersection. Where once there was a ramp to the viaduct, now there are two ramps to the tunnel. This is where southbound drivers in the tunnel will exit to reach SODO, the stadiums, and I-90 and I-5. This is also where drivers coming from I-90 or the stadiums will enter the tunnel for northbound SR 99.

Royal Brougham Way and First Ave intersection rendering

Note: A shared-use path along Colorado Avenue South will be built in a future phase of the project.

South end of the tunnel: South Atlantic Street and Colorado Avenue South

What’s changing:

  • New surface-street connection to Alaskan Way South
  • Colorado Avenue South with two-way traffic to Royal Brougham Way South

The changes around South Atlantic Street are less drastic but still worth knowing. The Atlantic Street overpass over SR 99 is now a complete connection to Alaskan Way (to the north) and East Marginal Way South (to the south). You can now reach both via South Atlantic Street by taking the ramp labeled below.

Colorado Avenue South (previously called East Frontage Road) is now a two-way street, providing a north and south route between South Atlantic Street and SR 99 on- and off-ramps. A common path from SR 99 southbound to reach I-90 will be to take Colorado Avenue south, then take a left turn onto South Atlantic Street.

South Atlantic Street and Colorado Ave intersection rendering

Note: At tunnel opening South Atlantic Street does not pass beneath the SR 99 overpass to Alaskan Way South. That connection will open later in winter/spring 2019.

 

Order: 4.5