Put a Lid on It! Five Principles for Designing Freeway Lids

In nearly every major city in the United States, urban renewal-era planning connected downtowns to newly developing suburbs with multi-lane highways, in the process destroying acres of city fabric. In rare instances, the highways tunneled under the city; more frequently they were elevated or placed in depressed channels to segregate the fast-moving traffic from “impediments” (that is, people). The result? Urban neighborhoods were divided and separated from the city center. Large swaths of the city were transformed into “no man’s land,” undesirable for pedestrian occupation, housing or commercial development.

Klyde Warren Park in Dallas © NBBJ/Sean Airhart

Today, from Duluth to Dallas to Denver (and many places in between), the channeled urban highways that cut through downtowns are being “lidded”. A freeway lid is just what you would imagine—a concrete shelf constructed over the road. The lid is capable of supporting parks, housing, office buildings, even local city streets. They have the potential to reconnect neighborhoods and to offer much-needed open space or development possibilities right in the heart of the city.

Recently we participated in a community-based design charrette to explore design ideas for lidding portions of I-5 through downtown Seattle. A number of recurring themes surfaced, including five essentials for designing a great highway lid:

Bikes and pedestrians want the dedicated infrastructure that cars already have

Direct, convenient routes designed primarily for cars are ubiquitous, but pedestrians and cyclists desire the same kind of paths designed specifically for them. Highway lids offer an opportunity within the city to provide greenways and viable off-street routes for non-motorized traffic. Like many cities, Seattle has public park gems, such as Volunteer Park and Discovery Park, but it lacks the comprehensive network of linear parks and greenways that are desirable to cyclists and pedestrians for off-street circulation.

…but the cars aren’t going away

In typical urban renewal fashion, highways tend to split cities with a disregard for neighborhood cohesiveness and local dynamics. Highway lids offer ample opportunity for new parks and pedestrian routes, but they also offer an opportunity to reconnect the street grid and correct the wrongs of past planning practices. In the case of Seattle, I-5 currently creates traffic choke points along its entire length, which could be mediated with more cross-highway connections. Design proposals will have to balance the needs of connecting the street network with the opportunity to create pedestrian-focused circulation.

People want great public spaces with fun programming

Current planning practices focus on programming for public spaces. Some of the most successful parks and plazas in the U.S. and abroad, such as the High Line in New York City or Klyde Warren Park in Dallas, have non-profit organizations dedicated to managing public events and inventing entertaining programming for a wide variety of users. Examples include rotating public art installations, movie nights, food trucks and lawn seating, farmers markets and craft fairs, and active uses like tai chi and yoga. Large, uninterrupted areas of open space offer the most flexible environment for dynamic, engaging programming.

…but private development can provide dollars and amenities

Verdant parks and sparkling fountains garner the most enthusiasm from the public, but it is dense private development that makes those public spaces financially possible. A good mix of office, housing and retail amenities will draw people to the site and ensure that public spaces will be vibrant with human activity. Good lid design needs to balance the need for large, flexible public spaces with development opportunities, and smart urban design guidelines should ensure new development is equitable and affordable.

Rose Fitzgerald Kennedy Greenway in Boston (with installation, “As If It Were Already Here,” by artist Janet Echelman) © NBBJ/Sean Airhart

No more mono-functional planning

Mono-functional planning—in this case, privileging the car by allowing a highway to cut through the city—was a mistake perpetuated in cities across America. Though a huge swath of green space in the city seems desirable, dedicating the entire lid as one large, public, open space is just another type of mono-functional planning that does little to physically reconnect neighborhoods. Conversely, dedicating the entire lid for private development misses the opportunity to design a city that caters to a plurality. Physical spaces (and development practices) must be designed to include a maximum range of users across class, race, religion, gender, physical ability and so on. This is no small task, and it is one of the most important challenges for planners and urban designers today.

Highway lids offer an opportunity to correct the planning mistakes of the past while also increasing the vibrancy and livability of the city. Going forward, lid design has to be more thoughtful, intricate and community-focused than the planning practices that put the highway there in the first place.

Thanks to Daren Crabill, Wyatt O’Day, Claire Showalter, April Soetarman, Amy Taylor and Keith Walzak for their input and participation in the I-5 charrette.