State Route 520 Montlake Lid and Land Bridge

Across Washington state, massive transportation infrastructure projects interrupt the social and ecological fabric of our cities and towns. What if there were a way to leverage investment in these projects to create more sustainable, connected places that bring people together rather than divide them? The SR 520 Lid and Land Bridge reveals the importance of design in collaboration with city officials, engineers, and the public to deliver thriving, people-centric places in this context. Creating natural habitat, pedestrian and bicycle networks, park systems, neighborhood open spaces, plazas, and transit facilities on top of, below, around, and in place of heavy grey infrastructure, this project demonstrates a larger project vision for community engagement, renewal and sustainability.

Over 50 years ago, State Route 520 sliced through Seattle’s historic Montlake neighborhood to establish a link across Lake Washington from Seattle and Interstate-5 to the growing Eastside communities. Since then, SR-520 has become a critical commuter route for employment centers on both sides of the water, as well as a seismically vulnerable structure where I-5 connects to the floating bridge. Known as the “Rest of the West,” this portion of the project involves developing and refining the proposed highway lid, land bridge and regional shared use path. From the highway, the lid and land bridge act as gateways to the treasured, historic context of the Montlake neighborhood and adjacent Washington Park Arboretum. Our team conducted a robust public engagement process, coordinating with King County Metro and multiple City of Seattle departments, and gathering input from stakeholders on numerous boards and commissions, and the general public.

Montlake Lid
The design embraces the locally established Olmstedian principle of “subordination,” where each element—lighting, walls, pavement, and landscape—contributes to the whole space. This approach informed design for the retaining walls, which incorporate a horizontal, extruded pattern encouraging voluntary plants and moss to become part of the overall composition. The reconnected street grid takes on the character of adjacent city streets to promote a seamless neighborhood identity and wayfinding. The large central open space offers a flexible green with subtle topography and perimeter plantings to buffer users from the surrounding active interchange. The large plaza is designed to streamline bus transfers, but also host community events and activities.

Land Bridge
The land bridge showcases a new human-scaled strategy that turns urban infrastructure into a place of lasting value. Carrying pedestrians and bicyclists over the highway, the structure and landscape prioritize vegetation over hard surfaces by inverting the traditional relationship of concrete girder to structural deck. The resulting sweeping meadow traverses a dramatic site, featuring a central 14-foot wide path flanked by gently sloping vegetated berms. Users are immersed in a quiet, pastoral environment, shielded from the noise and views of the vehicular traffic below. The gateway experience beneath offers views of a bridge dominated by a lush, attractive landscape. At the northeastern edge of the bridge, the path deviates to a unique, regional outlook framing views of Lake Washington, the floating bridge, and the Cascade Mountain Range beyond.