Project Overview

Background

In 2016, the City of Shoreline completed the 145th Street Multimodal Corridor Study and developed a preferred design concept for the corridor from 3rd Avenue NW to Bothell Way NE/Lake City Way (SR 522). Through an extensive public process and thorough technical analysis, the City tailored the planned improvements to maximize benefits while minimizing negative community impacts.

As a result of this study, Shoreline has received federal funding to complete design on two sections of the corridor: this interchange project and the portion of the 145th Street corridor from Aurora Avenue (SR 99) to I‑5. Both projects are now being designed.

Additionally, the City of Shoreline has received federal funding for design of a pedestrian/bicycle bridge across I‑5 at 148th Street that will connect directly to the new Shoreline South/145th Station. Sound Transit is also in the process of designing improvements to the 145th Street corridor from Lake City Way to the I‑5 interchange to support bus rapid transit.

Photo showing a long line of eastbound cars backed up on the bridge over I-5 on 145th Street.

145th Street, looking west across the bridge over I-5

Photo showing traffic congestion and a group of pedestrians crossing the street on the bridge over I-5 on 145th Street.

145th Street, looking east across the bridge over I‑5

Design

In 2018 and 2019, in collaboration with WSDOT, Sound Transit, City of Seattle, and King County Metro, the City of Shoreline evaluated several alternative design concepts. Through this process, the City and our partners worked to identify a design that would increase safety and efficiency for all travel modes, including cars, freight, transit, pedestrians, and bicyclists. Working in collaboration with multiple stakeholders, the City conducted digital modeling of traffic flows and intersection performance, and even tested a full-scale mockup of the roundabout design using Metro buses.

Initially, the City and our partners considered widening the 145th Street bridge to accommodate people walking and biking, constructing a new northbound I-5 button-hook on-ramp, and installing new traffic lights at the intersections at 5th Avenue NE and the I-5 ramps on the west side of the freeway. However, our analysis showed that multi-lane roundabouts would offer a greater improvement in safety and roadway capacity. Compared to signalized intersections, roundabouts will:

  • Improve safety for drivers by decreasing speeds and routing traffic in the same direction, reducing the severity of crashes.
  • Improve safety for pedestrians and bicyclists by separating them from vehicle traffic at well-marked and lighted crosswalks and reducing crossing distances.
  • Promote continuous traffic flow, reducing overall travel times and minimizing delays along the 145th Street corridor.
  • Eliminate the need for left-turn lanes on the bridge, creating space for a two-way, 10‑foot bike lane and a 5-foot sidewalk along the north side of the bridge.
  • Eliminate the need to widen the existing bridge, substantially reducing construction costs.
  • Reduce lifecycle operating and maintenance costs for the two intersections.

These improvements will address today’s and future transportation needs and improve safety and access along the corridor for decades to come.

Elements of the Project

The existing bridge over I‑5, which will connect the two roundabouts, will have ADA-accessible sidewalks on either side of it, allowing a seamless crossing for pedestrians. The pedestrian crossings will also include flashing beacons to increase safety. Bicyclists will use crosswalks to navigate the roundabouts and a two-way bike lane, separated from motorized traffic, to safely cross the bridge. The 148th Street Non-Motorized Bridge will support connectivity and safe access to the future Shoreline South/145th Station.

Overhead image showing the elements of the 145th Street & I-5 Interchange project, as well as four adjacent improvements planned by the City of Shoreline and other agencies.

Legend:

 Sidewalks

 Rapid-flashing beacons

 Two-way bike lane

 Connection to Jackson Park Trail

 Sound Transit, Shoreline South/145th Station roadway improvements

 City of Shoreline, 145th Street, Aurora Ave N to 1‑5 Improvements

 Sound Transit, Stride Bus Rapid Transit

 Seattle Department of Transportation, future traffic revisions and cycle track

 

Click on image to enlarge.

Interchange Fly Over

This video illustrates how all modes of travel will move through the roundabouts, including how drivers will travel through the roundabouts along with buses and trucks, and the routes pedestrians and bicyclists will use. The traffic shown in the video reflects the actual, projected traffic volumes at peak commuting hours, and how that volume of traffic will move through the proposed roundabouts.

The visualizations presented in the video are conceptual only and do not represent all elements of the final design of the interchange improvements.

Roundabouts Around Washington

Roundabouts are connected to many interstate on- and off-ramps in Washington. The 145th Street Interchange roundabouts will be multi-lane and similar in appearance to the examples shown in this slideshow.

Overhead photo showing the roundabout’s five entry/exit points and associated pedestrian crossings, and landscaping in the center islands and medians.92nd Ave NE/Points Dr NE/NE 33rd St/SR 520 westbound off-ramp, Medina, WA
Photo showing the landscaping and truck apron in the center the roundabout as a car drives through.92nd Ave NE/Points Dr NE/NE 33rd St/SR 520 westbound off-ramp, Medina, WA
Photo of cars driving through, and exiting, the roundabout.W Lake Sammamish Pkwy SE/I-90 westbound ramps, Bellevue, WA
Photo of a multilane roundabout with two lanes of traffic entering and two lanes of traffic exiting the roundabout.W Lake Sammamish Pkwy SE/I-90 westbound ramps, Bellevue, WA
Photo focused on the landscaping in the center of the roundabout.NE 36th St, Redmond, WA
Photo focused on the welcome sign in the center of the roundabout.E Valley Mall Blvd/I-82 ramps, Union Gap, WA
Photo focused on the welcome sign and the directional signage in the center of the roundabout.E Valley Mall Blvd/I-82 ramps, Union Gap, WA
Photo focused on the landscaping, welcome sign, and directional signage, in the center of the roundabout.SR 202/I-90 eastbound ramps, North Bend, WA

Roundabout Rodeo

To ensure that buses will be able to safely navigate the roundabouts, the WSDOT Regional Transit Coordination Division assisted King County Metro in organizing a “Roundabout Rodeo” with Seattle Department of Transportation (SDOT) and the City of Shoreline. This exercise is a proven method for testing the functionality of a proposed roundabout design. The design was laid out on the ground using paint and traffic cones. Metro operators were able to successfully drive in, around, and out of the roundabouts. This video captures the event in action.