The goal of bridges is to span across rivers or valleys, streets or highways, rail yards or railroad tracks. Essentially a structurally supported deck, a bridge is a connector enabling movement between whatever the bridge connects. But a few bridges achieve another goal: If the bridging deck supports activities and structures, it is a destination as well as a connector.

With sufficient length and width, a bridge can become in effect built land, a place for residential, commercial and recreational development, a “reconstituted ground plane” in architectural parlance.

A bridge that connects and creates land and land development opportunities is not a new idea. The Ponte Vecchio in Florence, Italy, first built in Medieval times, is the iconic prototype of a destination bridge hosting income-producing real estate. Three stone arches gracefully step across the Arno River to support a narrow street. Lining each side of the street and surmounting the bridge is a multi-level agglomeration of small shops, work spaces, offices and apartments.

Modern-era bridging strategies are gaining traction in Washington and elsewhere, especially where natural or city-splitting infrastructure barriers exist; where air-rights development is technologically and financially feasible; and where infrastructure owners are willing to grant development air rights. And topping the list of barriers worth bridging are obstructive transportation corridors — expressways and railways — whether elevated, sunken or on-grade.

In D.C., Capitol Crossing will be a 2.2 million-square-foot, mixed-use project built atop a street-level, structural deck spanning across Interstate 395 and its chasm slicing through downtown’s eastern flank. The site is bounded on the north and south by Massachusetts Avenue and E Street NW, and on the east and west by Second and Third streets NW.

Bridging over the sunken, six-lane I-395 freeway will be technically challenging, as the freeway cannot be closed during construction. But the payoff will be creation of three new city blocks on which new office and apartment buildings can be built. The platform and street-level destinations also will help reconnect urban neighborhoods split apart by the freeway.

Burnham Place likewise will be a high-density, mixed-use, air-rights project built atop a structural deck spanning across multiple rail platforms and tracks north of Union Station. Long-range plans envision a total makeover of the transportation complex behind the iconic station, plus a new, north-facing station entrance and plaza at H Street. When the project is done, D.C.’s increasingly vibrant NOMA (North of Massachusetts Avenue) neighborhood will be better connected functionally and aesthetically to Union Station and Burnham Place.

One other unique D.C. bridging project is in the works: the 11th Street Bridge Park. A new pedestrian deck spanning the Anacostia River is to be built on existing bridge piers left standing after demolition of the old 11th Street bridge. The project’s key conceptual goals include: making the bridge an artfully designed destination encompassing recreational, cultural and educational activities; enhancing knowledge of and interaction with the Anacostia River environment; and providing a strong physical connection unifying both sides of the river, most notably Wards 6 and 8.

Outside Washington, a worthwhile model and proof of concept for bridging, both to connect and to create a desirable urban destination, already exists. In Dallas, Klyde Warren Park sits atop a structural concrete deck spanning sunken, city-splitting State Highway Spur 366, the Woodall Rodgers Freeway. Constructing the 1,200-foot-long deck posed technical challenges similar to those facing construction of the Capitol Crossing deck spanning D.C.’s I-395.

Completed and dedicated in 2012, Clyde Warren Park was a long overdue city enhancement, as downtown Dallas encompasses few public parks and relatively little housing. Thus, thanks to construction of a new piece of urban land, the 5.2-acre, three-block-long park finally provides street-level, civic open space in the heart of Dallas.

The park’s amenities are numerous. A spacious performance pavilion and a popular restaurant anchor the center of the park. Unlike many urban parks, well-equipped public restrooms are provided. A children’s play area, botanical garden, dog park, water fountains and ample seating attract visitors, all helping to animate the space. The well-landscaped, well-lighted park is continually programmed throughout the year for concerts, music festivals, dancing, games and small-scale, staged activities such as puppet shows.

At the same time, Klyde Warren Park knits back together the severed urban fabric of the adjoining downtown Dallas neighborhoods, split apart for decades by the sunken freeway. The park reconnects streets and walkways, improving pedestrian and vehicular traffic flow while further activating the park. And developers are building more downtown housing in response to a market perceiving increasing downtown urbanity, to which the park contributes.

Constructing structural decks on which to build is a complex and costly process. Thus, it only makes sense in places with very good transportation access, where market-responsive uses and high densities can be developed, and where highly attractive amenities can be provided. With earth-bound urban land becoming ever more expensive, perhaps building bridges to create new land will become both increasingly necessary and desirable.

Roger K. Lewis is a practicing architect, a professor emeritus of architecture at the University of Maryland, and a regular commentator on “The Kojo Nnamdi Show” on WAMU 88.5.