I-5 Lid Feasibility Study


In December 2020, the Seattle’s Office of Community Planning and Development (OPCD) published the I-5 Lid Feasibility Study. While preliminary, the study ultimately concludes that lidding more of Interstate 5 between Madison Street and Denny Way is both technically feasible and can improve quality of life. This study does not recommend a preferred design option. Many next steps are needed to advance the project.

The study says, “Lidding I-5 through downtown presents an opportunity to tackle some of the most pressing challenges facing Seattle. This requires contemplating opportunities to increase affordable housing, support and protect local industries and small businesses, and make vital investments in infrastructure, community facilities and open space.” Further, “The robust fiscal and economic benefits of a lid, in addition to the public benefits described in this study, make a lid project worthy of consideration despite the significant funding challenges.”

This page describes the most important findings from the feasibility study, from the perspective of the Lid I-5 campaign. For further details, the study and supporting documents may be viewed at the links below.


All files are PDF format. Some files are large and may take several minutes to download.

See the OPCD project website for meeting materials. Other documents supporting the Lid I-5 effort are on our library page, and academic studies can be found on our research page.

Image by WSP (click to enlarge)

Key Findings

The study provides a wealth of information and data. Below are some key findings that are important for community members, stakeholders, and decision-makers. More details on public benefits and cost estimates are in the following sections.

Public Benefits

Lidding I-5 could create up to 17 acres of new public land and could address multiple public needs. Likely public benefits are:

  • Advance equity for the 40,000 people who live within walking distance of the study area by reducing freeway noise, increasing park access, adding transportation choices, and possibly creating space for much needed housing and civic functions like community meeting places. These residents are as racially diverse as Seattle as a whole, are mostly renters, and have much lower incomes than the citywide median.
  • Add new park space in Seattle’s most dense and park-deficient neighborhoods, support more affordable housing amid a historic housing crisis, add commercial space for local businesses and startups, and add new capacity for civic and cultural functions (like a Downtown school and community center) as the population increases.
  • Reduce noise and air pollution near I-5 and protect our waterways and marine habitats by treating stormwater runoff.
  • Reconnect the local street grid and improve mobility for thousands of people walking, bicycling, and riding buses and light rail. This includes widening the Hubbell Place connection at Freeway Park.
  • Create thousands of construction jobs and permanent jobs, with potential economic impacts of over $3 billion annually.

Other Considerations

  • Ramps accessing the freeway present a significant challenge to maximizing the possible lid area and creating a quality urban design. Removing ramps could both make it easier to build lids and may improve freeway through-traffic in the Downtown bottleneck. This requires a federal Interchange Justification Report and a transportation network study, which has already been proposed by the Imagine Greater Downtown initiative.
  • Building lids over the current freeway is feasible, and could be staged with minimal traffic disruptions and would not require any long-term closures. However, the freeway’s obsolete design and aging structures would make this challenging. The Washington State Department of Transportation (WSDOT) has determined I-5 in Seattle needs major work to resolve earthquake vulnerabilities and traffic flow problems. It would almost certainly be more efficient to integrate a lid project into a larger preservation or retrofit of the freeway which also changes ramp configurations, both for cost efficiency and streamlined engineering. (Note: Freeway widening is not physically possible in the study area.)
  • The cost of lidding I-5 as a standalone project is comparable to other civic and transportation projects of this scale and public importance. Cost reduction strategies like reducing or eliminating off-site parking are identified below.
  • Cost will vary block-by-block due to the different size, shape, and loading capacity of each block. The study area was divided into Areas 1-4 as illustrated below. The study analyzed all four Areas being constructed in sequence, but it would also be feasible to build any Area independently.
  • The project will not be funded by a single source, due to both its size and the variety of possible uses for the new land. The study made no assumptions about funding sources but identifies a number of public and private options.
  • A scenario that maximizes private involvement would result in significant public revenues, but would not fully offset the initial cost of lid construction in a reasonable time frame.
  • Between Spring and Seneca Street, altering or removing the Freeway Park box garden would allow cleaner lid framing and more usable lid space, but this must be sensitive to Freeway Park’s recent addition to the National Register of Historic Places.
  • Providing a fire and life safety facility on the lid with 25,000 square feet was assumed in all development program test cases, given that the lid will be technically considered a “tunnel.” Requirements for traffic tunnels such as ventilation, fire suppression, and lighting are included in the cost estimates.
Image by WSP (click to enlarge)

Study Approach

There are infinite possibilities for the mix of land uses on the lids, so the study took a “bookend” approach to examine the most basic and the most extreme development options. This formed the basis for three Test Cases that form the core of the feasibility study.

  • The “leanest” approach delivers a core public benefit at the lowest cost, and lidding only the easy sites. Ramps are not removed. This forms the basis for Test Case 1.
  • The “robust” approach assumes a desire to maximize the lid area and development capacity. Ramp removal is on the table. This forms the basis for Test Case 2.
  • Lastly, Test Case 3 is a mid-density hybrid using a mixed approach to development, with public parks and civic uses co-located with with affordable housing and market-rate development.

The graphics below illustrate the assumptions for the leanest and robust approaches, and the consequent maximum load levels. The load levels are directly related to length of spans that must be crossed, which is determined by where columns and walls can be placed on the freeway and between lanes. See the report and the Technical Feasibility Memorandum for detailed structural dimensions and diagrams. The lowest load-level can only support open space and parks. Low-rise load levels can support 7-story buildings. Mid-rise load levels can support 15-20 story buildings. High-rise load levels can support up to 45-story buildings (this is only possible where the buildings can sit above solid ground on edges of the lid).

Images by WSP (click to enlarge)

Public Benefits and Cost Estimates


The benefits to Seattle, the region, and the state are potentially enormous, and will outweigh the cost of initial investment. The following section describes the public benefits in detail.

Development Capacity

The study built three Test Cases to examine potential development capacity and budget implications. Test Case 1 is a public park. Test Case 2 is high-density private development with no public features. Test Case 3 is a mid-density hybrid with a mix of public parks, civic buildings and affordable housing, and private buildings. Policy assumptions around parking, affordable housing, and civic space influenced the test-case configurations outcomes (see the Test Case Memorandum for details).

The graphics below summarize the development potential, with total lid sizes ranging from 11 to 17 acres. The following sections describe what this capacity means for the Seattle community.

Image by WSP (click to enlarge)
Demographics and Who Benefits

Demographic and economic trends in the Center City are resulting in new demand for the services and conveniences that typically exist in dense residential neighborhoods. They also show that a lid project will benefit a broad cross-section of the community. Contrary to popular belief, the Center City neighborhoods are not particularly White or affluent. The area is home to a broad mix of low-income families, people of color, and children.

Image by WSP

Over 40,000 people live within a 15 minute walk of the lid study area, including some 4,800 children. With respect to race and ethnic identity, the area is a microcosm of the Seattle population as a whole; approximately 36 percent of residents citywide and 36 percent of people in this study area are people of color. Over 80 percent of these residents are renters, compared to 56 percent rental tenure citywide.

The study area median household income in 2017 was about $64,000 compared to $85,000 citywide. Over 15 percent of people were living below the poverty level in 2018, which was higher than the citywide 12 percent. Approximately 11,700 households within the study area are considered low-income. The area is home to about 2,150 social housing units, according to section 7.5 of the feasibility report, and 600 of those units are within one block of Interstate 5. The study area has the highest concentration of social housing in Seattle (see, for example, property maps for Seattle Housing Authority, Bellwether Housing, Community Roots Housing, and the multifamily tax exemption program).

The study says, “The lid could provide affordable space to marginalized communities in an area with the highest access to opportunities. Equity is a major priority for Seattle, and with escalating rents, displacement is pushing out the most vulnerable people and businesses from urban neighborhoods. The lid could create physical space and catalyze investment in communities that have been disenfranchised to improve outcomes for populations that have been hardest hit by historical disinvestment, displacement and gentrification.”

Lid project amenities like parks, new street connections, new commercial services, and new cultural offerings could indeed have a direct and positive impact on quality of life for the area’s residents. However, as with any major infrastructure investment, the risk of displacement must be considered and mitigated. The feasibility study offers a very preliminary look at displacement risk using existing City of Seattle data. The map below shows the risk is a mixed bag. Rental rates and property values are already fairly high in the study area.

Seattle’s zoning code does not require parking in the study area, but the feasibility study starts with an assumption that market-rate housing and commercial development would still include thousands of parking spaces, with 90 percent of parking provide off the lid. This means adjacent existing properties would need to be demolished to make room for parking garages. If off-site parking can be made unnecessary through multi-modal transportation policy and market changes in the future, significant cost savings can be realized and displacement can be avoided.

The study notes that new affordable housing could offset displacement risk. Research by Alberta Bleck at the University of California, Berkley, examines how Seattle’s Office of Housing community preference policy could address past harms from the construction of Interstate 5 (which displaced 40,000 people citywide in the 1960’s). Further, Lid I-5 will advocate for the project sponsor to explore other strategies as the project advances. These could include stewarding an equitable community-based master planning process, setting aside space for small and local businesses and startups, targeted hiring and workforce development during construction, “tenant opportunity to purchase” programs, homeownership subsidies, and community land trusts. See a toolkit of strategies by the nonprofit organization Greenlining.

Image by WSP (click to enlarge)
Affordable Housing

The increase in housing costs is one of Seattle’s most pressing issues, driven by the fact that Seattle has added approximately 2.5 jobs for every home built between 2010 and 2018. The study found the lid could lead to a significant increase in the city’s housing supply, in an area where little land is available near the jobs and services in the Downtown core.

The study assumed Test Case 2 would only build market-rate housing, and would pay $150-215 million into Seattle’s citywide Mandatory Housing Affordability (MHA) fund. This would potentially support 390 to 630 affordable housing units (using local per-unit costs provided by Sightline Institute), and those units would be built in neighborhoods across the city.

In Test Case 3, of the new housing on-site 40 percent would be rent-restricted, with a potential of 533 affordable units (assuming average 900 square feet units per the Department of Commerce). Affordable housing could be designated for special needs populations such as veterans, seniors, and the formerly homeless. Test Case 3 also has market-rate units that contribute $32-39 million to the MHA fund.

By way of comparison, the Madison/Bolyson project on First Hill will include approximately 260 homes, and Seattle Housing Authority’s Denny Terrace building in Capitol Hill has 222 units. Any housing component of the lid, whether market-rate or affordable, will depend on the project’s funding plan, community needs, and the design approach.

Park Space

In public outreach by Lid I-5, the need for more public parks and green space has been the number one community priority. Consequently, parks were a major emphasis in the feasibility study. Test Cases 1 and 3 create 8 to 10 acres of new park space, expanding upon Freeway Park and Plymouth Pillars Park. Comparatively, South Lake Union Park is 4.5 acres and Cal Anderson Park is 11 acres. Test Case 2 does not create any public parks.

The Center City has a considerable gap in parks and public open space compared to its population and peer cities. More parks, trails, playgrounds, and sportfields are important for livability and supporting the health and recreation needs of urban residents. This is especially important for the thousands of families living in rent-restricted housing within the study area. A University of California study quantified equity impacts for existing lid parks across the nation, and found that Freeway Park scores highest among lids in the Seattle area, showing more parks here will have a positive equity impact.

Images by WSP (click to enlarge)
Economy and Taxes

Lidding Interstate 5 under Test Cast 2 and 3 would have the greatest long-term economic benefits. The following figures below account for direct, indirect, and induced impacts. Between the two scenarios, 1,200 to 2,600 construction jobs would be generated. Permanent jobs would be between 10,600 and 29,000, mostly depending on the amount of real estate development on the lids. Annual economic activity would be $2.5 billion to $3.7 billion, which is driven by retail activity, commercial and residential leasing, maintenance and operations, service contracts, and other similar transactions.

In comparison, the lid study references the Waterfront Seattle project, which is anticipated to result in ongoing economic activity of $288 million and 2,385 permanent jobs. The Port of Seattle’s improvements at Terminal 5 will lead to an estimated $2 billion in direct business output and 6,000 jobs.

Considering all cases, property values within 1,000 feet of the project could increase $43 million to $129 million. Annual local and state tax revenues in Test Cases 2 and 3 would increase between $62 million and $172 million. These value increases could potentially be captured to help pay for initial construction or ongoing maintenance and operations.

Environment and Health

The lids could be designed to enhance the urban environment and our local utility systems. The consultant team estimates 30 percent of the runoff of the Capitol Hill basin would could be treated or retained on the lids, reducing runoff and pollution to our waterways and marine life, and reducing demand on the sewer system.

A lid could reduce direct exposure to air pollutants within the study area (further quantified by an American Journal of Public Health study). The central Seattle microclimate might also benefit by modifying the 0.8 miles of road surface. Urban heat islands elevate local air temperatures by three to four degrees as compared to the air in neighboring, less developed regions or areas with increased vegetated cover

The study site is burdened with considerable freeway noise that negatively affects quality of life, enjoyment of outdoor spaces, and property values. Ambient noise over 66 decibels qualifies for possible mitigation with sound walls or berms, and an environmental impact statement for another project in the corridor showed that existing noise levels range from 70 to 78 decibels. A lid would act as a likely noise barrier.

Street Connections and Traffic

The construction of I-5 severed nine of 18 east-west connections, particularly Minor, Yale, and Terry Avenues. The loss of these connections disrupted the traditional grid. The recent growth of the Capitol Hill, First Hill, and South Lake Union neighborhoods has made reconstruction of the lost connections increasingly important. And despite the uncomfortable conditions and traffic safety issues in the area, the study found that several thousand people walk and bike across I-5 each day.

Five current and future Sound Transit Link light rail stations are within the 15-minute walkshed of the study site, with the closest being the future Midtown Station off Madison Street. With over 30 routes, King County Metro and Sound Transit provide a dense network of bus routes that serve the study area. New lids could provide more safe and convenient connections for people walking and wheeling, including those taking transit to and from their destinations.

Civic Uses

For public uses within buildings, a specific program was not defined by the feasibility study. These would be spaces such as community centers, cultural spaces, libraries, schools, and fire stations. Public or private theater and performance spaces might also be considered in this category. Presumably, the load capacity for civic uses could swap out with commercial uses (described in the next section). The civic program will be determined by a future master planning process.

Seattle Public Schools has long struggled to acquire land or space for a downtown elementary school, despite school-age children being the fastest-growing population group in the area. The map below shows the gap in school coverage in the greater Downtown area.

The study area also does not have any type of public community center that offers free or low-cost access for meetings and activities for youth, families, and seniors. According to Seattle’s 2016 Community Center Strategic Plan, a community center should be located in every official Urban Center, within one mile of every Seattle household, and each center should serve a residential population of 15,000-20,000 people.

More research on the need for civic uses in the area is included in this research article by Scott Bonjukian.

Image by WSP (click to enlarge)
Commercial Development

The lid could host significant commercial development (retail, restaurants, office space, and hotel rooms). This use would need to be the most carefully considered, because high-end commercial development would not necessarily contribute as much to the public trust as the other benefits described above. However, commercial uses generate significant revenue that could help pay for part of the lid capital cost.

Test Case 1, the public park, includes pavilions for modest opportunities for retail uses to activate streets and public spaces. Test Case 2 includes over 5 million square feet of commercial space. Test Case 2 includes about 2 million square feet of commercial space. Comparatively, the greater Downtown area currently has 79 million square feet of office space.

The future demand for commercial space in the Downtown area is an open question as Seattle grapples with the devastating impacts of the COVID-19 recession. Downtown is still the heart of the region, though: Despite being less than 6 percent of Seattle’s landmass, it accounts for approximately 50 percent of the economic activity in Seattle, including more than half the jobs, about a third of brick-and-mortar retail sales, more than a third of leisure spending (including dining), and half the taxes paid by businesses in the city. As of December 2020, there are 54 residential and commercial projects under construction in the area. See more in the Downtown Seattle Association’s State of Downtown 2021 Economic Report.


The study provides very preliminary cost estimates for developing lids that support each of the three Test Cases. These estimates are based on design that is less than 5 percent complete and they do not consider several external factors. The costs do not include the repair or replacement of Interstate 5 nor the cost of any vertical development on top of the lid.

Notably, the estimates do include appropriate but very significant multipliers above the core construction costs: a 20 percent construction contingency, plus a 30 percent risk factor. The approach to the cost estimates and multipliers is explained in the graphic below.

Image by WSP (click to enlarge)
Initial Construction

The cost estimates for each Test Case are summarized as the following:

  • Test Case 1 (11 acres, public park): $966 million
  • Test Case 2 (15-17 acres, high-density private): $2.3 to $2.5 billion
  • Test Case 3 (15-16 acres, mid-density hybrid): $1.5 to $1.7 billion

A breakdown by Area 1-4 for each Test Case is shown in the following table. The cost varies in each Area because of different designs proposed by the consultant team and the different size and shape of each block. The difference between Test Case 1 and Test Cases 2/3 is so large because the more a lid has to hold up, the more expensive it is to build. Structural requirements to hold up buildings is estimated to be 50 percent more than the cost of supporting parks. Test Cases 2 and 3 have a range of size and cost estimates because they explored removal of the Olive Way ramps to create more lid area. 

Image by WSP (click to enlarge)

The preliminary estimated costs are comparable to other civic projects of this scale and public benefit. Test Case 3 is only slightly more than the I-5 reconstruction effort in the Tacoma, for example, and also less than the total value of the Yesler Terrace redevelopment. Even the most intensive scenario, Test Case 2, is less than half the cost of the entire Waterfront Seattle program. Other examples are shown below.

Image by Lid I-5
Cost Considerations

Beyond the multipliers, the estimated lid costs are influenced by several factors. Construction prices in Seattle have long been higher than the national average, and material and labor costs continue to rise. Importantly, this study area also has unique challenges due to steep topography, multiple ramps in the corridor, and earthquake safety requirements that are not reflected in nationwide lid project data. The engineering is also complex compared to other lid projects. The freeway lanes curve, there are 15 independent bridge structures to work around, and the freeway is supported by 33 different wall structures.

Grade variation cross-section showing an east-west section at the Spring Street bridge with the dashed green and blue lines showing the heights of the adjacent bridges to the north and south (Image by WSP)
Image by WSP

Relatedly, the study did not consider rehabilitation or retrofit of the Interstate 5 freeway itself. According to the I-5 Systems Partnership, the freeway is nearly past its design life, the structures are vulnerable to earthquakes, and the freeway design is obsolete. If lids were built in sync with an I-5 preservation project, major cost efficiencies could be realized and the overall lid capital costs would likely be reduced. Savings could be realized in many areas, such as combined engineering, design and environmental review processes, material and labor prices, and consolidated construction staging and traffic management. The Seattle lids over Interstate 90 and State Route 520, all built during construction of those freeways, demonstrate this approach (see construction photos and videos for the Montlake Lid).

It is too early to determine funding and financing methods, but the feasibility study says funding would not come from a single source. Similar to other infrastructure projects, the magnitude and complexity of this project could require multiple municipal, county, regional, state, and federal sources and could also rely on philanthropic or private sector contributions. The funding sources will also depend on the uses on the lid. Parks, affordable housing and civic uses will require public funding, while private buildings would imply significant private funding.

Potential Cost Savings

Parking is a major cost factor. Seattle’s zoning code does not require parking in the study area, but the consultant team assumes the developers of market-rate housing and commercial buildings would likely still include thousands of parking spaces to meet market demand. Test Cases 2 and 3 assume 90 percent of parking would be provided off-site (not on the lid). This means adjacent existing properties would need to be demolished to make room for parking garages. Not only is this a major equity and displacement concern, but off-site parking represents 20-22 percent of capital costs for Test Case 2, and 10 percent of capital costs for Test Case 3. If off-site parking can be made unnecessary through multi-modal transportation policy and market changes in the future, significant cost savings can be realized and potential displacement can be avoided.

An alternative approach to Freeway Park (Area 2) could save significant costs. In Test Case 2 and 3, the consultant team modeled mid-rise buildings in the park’s gap over the University Street ramp, costing $167-217 million (discounting the Hubbell Place walkway cost). This represents 11-12 percent of capital costs for Test Case 2, and 10-11 percent of capital costs for Test Case 3. While adding buildings so close to the park could aid in activation, it might not be the most appropriate way to leverage this existing open space. One of the reasons for Freeway Park’s perceived seclusion and safety problems is the numerous buildings that have grown up around the park. Further, this site would be fairly challenging to provide vehicular access, with limited street frontage. Expanding Freeway Park would cost less, still reduce traffic noise, add two acres of usable space for a variety of recreational activities.

The gaps in Freeway Park (image by Lid I-5)
Ongoing Maintenance and Operations

The study included a long-term look at operations and maintenance of the lid structure, parks, and any civic facilities that might be included. Annually, Test Case 1 would require $4.3 million, Test Case 2 would require $5.7-5.9 million, and Test Case 3 would require $4.6-4.9 million. These costs do not include air rights payments to the Washington State Department of Transportation (WSDOT) nor any debt payments on construction funding.

The study says there are many options to pay for these costs, such as local funding and private sponsorships. In addition, the residual land value in Test Case 2 is worth $20-26 million per year, and $3-4 million per year in Test Case 3. See page 99 of the Lid Feasibility Study Summary Report for more details.


Projects of this size require consideration for how the lids will be procured, designed, constructed, financed and managed. The governance model should be nimble enough to allow for innovation that can unlock the project’s full opportunity. Before any definition is made about the project-delivery mechanism or governance structure, the project should first undergo visioning and master planning exercises that reflect the role of the community and create clear policy goals.

There would be stakeholder comfort and institutional knowledge to execute a public governance model, which is considered “conventional.” There are indications the Federal Highway Administration considers private-revenue generation over a highway permissible as long as all safety and access considerations are evaluated and met to the degree required by WSDOT. The public-private model shows significant promise, but the State of Washington lacks a local precedent and a model of this nature could require intensive oversight from the public sector.

Image by WSP

WSDOT is authorized to engage in air rights leases under RCW 47.12.120 and has a history of doing so. For instance, the Seattle Municipal Tower was constructed under a 77-year air rights lease. The Washington State Convention Center was similarly constructed via an air rights lease with WSDOT, currently consisting of a fixed payment amount of $475,000 per year. The experience from these arrangements demonstrates the feasibility in executing these types of agreements. An air rights lease payment was not required of other recent lid projects on I-90 and State Route 520 because they were classified as mitigations integral to a transportation project.

A public development authority (PDA) is one possible approach. PDAs are best used for unusual endeavors, where the parent municipality is not the most appropriate body to oversee projects beyond what is normally carried out by the municipality. It is anticipated that a PDA could be used for this project even if the ultimate use of the land on the lid is varied, such as parks, pavilions, low- and middle-income affordable housing, private development, and other uses with multiple ownership entities. Local PDAs and similar organizations operate Pike Place Market, Seattle Chinatown-International District PDA (SCIDpda), and the Capitol Hill Housing Improvement Program (Community Roots Housing).

Public Outreach

The feasibility study project included targeted, equitable outreach led by the Seattle Department of Neighborhoods and consultant team firm Rule Seven (see the outreach report). Outreach consisted of interviews to underrepresented stakeholders including the Equitable Development Initiative, Central Area Collaborative, Downtown Emergency Services Center, Horizon House senior living community, and the Five City Commissions Focus Group (representing the Seattle’s Women’s, LGBTQ, People with DisAbilities, Human Rights, and Immigrant and Refugee commissions). An online survey seeking general public feedback was offered in English, Chinese, Somali, Spanish, and Vietnamese.

Feedback from this effort was very helpful, confirming community interest and support for lidding I-5. There was particular support for additional parks with active programming, green space in general, affordable housing for Downtown workers, and space for human and social service providers. Participants said any new public space should be freely open to the general public, and include practical functions like restrooms and food sales, be physically accessible to people with disabilities, and be designed to make people feel welcomed (Freeway Park’s current design was cited as a safety concern). Several groups pointed out the opportunity for construction jobs, especially for underrepresented minorities in the trades.

Important concerns also arose, such as questions around equity, earthquake safety, air and noise pollution, and homeless encampments and services. There was some opposition to the concept of dense, high-rise development on the lid, especially if that development relies on a significant amount of public money for construction. Similarly, several groups said the lid project should not be designed as a money-making opportunity. However, if new public revenue is generated by the project, some participants said the new dollars should go towards anti-displacement and equitable development efforts.

Many people want to continue to be part of the conversation and to share the idea with their communities. DON’s work built upon the years of outreach by the volunteer Lid I-5 Steering Committee, which has included workshops, presentations, tours, media interviews, and online engagement. Continued outreach to assess values, preferred lid design, and concerns will be needed. Lid I-5 will continue to play a role in outreach. Over the long-term, to widen and deepen public engagement this project will require significant funding and staff resources.

Next Steps

The next phases of the project should include a more extensive investigation of project vision, scope, and sponsorship. Some next steps and actions for project development are:

  • Funding for the I-5 System Partnership to advance system-wide scenario analysis and community connection concepts for the urban Puget Sound highway system.
  • Agency alignment, institutional coordination, and partnership between the City of Seattle, WSDOT, and the Federal Highway Administration (FHWA) on project goals, project boundaries, a coordination mechanism, and policy alignment.
  • Community engagement that provides feedback into the development of the lid project through all future phases of analysis with a commitment to advancing racial equity, ending race-based disparities, and establishing a practice of co-powering with communities of color to define equity-centered processes, investments and outcomes.
  • Downtown Seattle transportation and traffic impact study to analyze impacts to the surface street network and mainline I-5 in order to improve project viability. This would asses impacts on ramp removal or modification, identify access points to I-5 from the study area, construction staging, and functionality during and after the lid is built.
  • Geotechnical explorations and assessment of site conditions to ensure better understanding of project cost and design. This would include structural assessment to determine the future of the independent bridges and assets on I-5 within the boundaries of the project to determine rehabilitation, retrofit, and preservation needs.
  • Development of a Preferred Alternative and Master Plan to clarify a project vision,  a project sponsor, and a lid project purpose and need statement. The project sponsor could initiate a Planning and Environmental Linkage study to identify a preferred alternative for a lid project, which would help streamline compliance with the National Environmental Policy Act and Washington State Environmental Policy Act.
  • Engineering and design (up to 30-percent design) would follow, with consideration of phases of construction and coordination for traffic management and utility impacts. Whether this phase is carried out by the public sector or the public sector with private partners would need to be determined. A fully integrated urban design and engineering approach is commended.
  • Identification of capital project funding opportunities via relevant state, regional, and local levies, including the Connecting Washington Replacement, MOVE Seattle Levy Replacement (after 2024), Seattle Parks & Recreation Levy, and other potential levies based on potential lid uses. The following table lists other potential sources.
Image by WSP (click to enlarge)

Background Information

The following sections provide background information on how the feasibility study was initiated.

Study Funding and Timeline

The study funding was provided by the Washington State Convention Center (WSCC) Addition public benefits package. These benefits were required in exchange for multiple street vacations. Lid I-5 partnered with other groups to form the Community Package Coalition (CPC) to advocate for millions of dollars in funding for affordable housing, transportation improvements, and Freeway Park preservation. The total package was valued at over $90 million, and the feasibility study was funded at $1.5 million.

The many steps to approve and fund the feasibility study included the following.

  • December 16, 2015 – The Lid I-5 team, as part of the Pike/Pine Urban Neighborhood Council, first publicly presents the lid concept at a “lunch and learn” event with Seattle City Council. Over 100 people attend. The team goes on to build public awareness through multiple workshops, tours, books, and media interviews through 2016 and beyond (described elsewhere on this website). These activities also demonstrate to elected leaders and decision-makers that there is support for the lid concept.
  • December 7, 2016 – The WSCC invites community organizations to an open house to share ideas for the Addition project’s public benefits. Lid I-5 attends and advocates for funding a lid feasibility study, tying the idea to the original WSCC which sits over I-5 and the Addition project that sits adjacent to I-5. The CPC forms after this event.
  • February 16, 2017 – The WSCC includes $250,000 for the lid feasibility study in their initial proposal to the Seattle Design Commission. After months of negotiation with the CPC, in October the WSCC agrees to fund the full $1.5 million feasibility study amount proposed by Lid I-5.
  • November 17, 2017 – The Seattle Design Commission approves the WSCC’s public benefits package.
  • May 7, 2018 – The package is approved unanimously by the full City Council, after receiving the recommendation of the Transportation Committee on May 1.
  • August 14, 2018 – The WSCC Addition breaks ground.
  • December 13, 2018 – The request for proposals on the feasibility study is released. The Office of Community Planning and Development (OPCD) worked intensively with the Lid I-5 team to craft the solicitation during the preceding months. A packed pre-submittal conference on December 20 demonstrates intense interest, and OPCD ultimately receives 12 responses from consultants.
  • February 2019 – OPCD awards the feasibility study contract to a consultant team led by WSP (see an excerpt of their proposal). The City’s selection committee includes a member of the Lid I-5 Advisory Council with infrastructure development expertise.
  • 2019 – The consultant team meets several times with the advisory Feasibility Study Committee for feedback and to present findings (public meetings on March 26, June 11, August 22, October 3, and December 11). The 16-member FSC includes nine representatives and technical experts from the Lid I-5 Steering Committee and Advisory Council.
  • December 22, 2020 – The feasibility study is publicly released. It was originally due in April but is delayed by the impacts of the COVID-19 pandemic and review by Mayor Durkan’s office.
  • January 21, 2021 – Final meeting of the Feasibility Study Committee.

Study Consultant Team

WSP is a global engineering firm with an extensive portfolio of bridge, tunnel, and highway work. WSP has an office in Seattle with local experience, and the company has advised on several freeway lid efforts nationwide. They teamed up with a number of firms who provide subject matter expertise:

  • OJB Landscape Architecture (designers of Dallas’ highly successful Klyde Warren Park)
  • HR&A Advisors (economics, with work on several freeway lid projects)
  • Magnusson Klemencic Associates (engineering)
  • BergerABAM (engineering)
  • Framework (urban design)
  • Enviroissues (public outreach)
  • Shiels Obletz Johnsen (real estate project management)
  • Rule Seven (marketing)