A rendering of the proposed Elizabeth Square development near the downtown Silver Spring Metro station. (Lee Development Group and Housing Opportunities Commission of Montgomery County)

Transit-oriented development, or TOD, is rapidly gaining momentum in the Washington region and will likely become a  key component in this area’s efforts to address traffic congestion, pollution and quality-of-life issues.

TOD has become the dominant public- and private-1sector planning strategy for real estate development and redevelopment throughout the metropolitan area and isn’t limited to downtown Washington. TOD projects are under way or being envisioned in Maryland and Virginia counties.

Arlington County’s Rosslyn-Ballston corridor, with five Orange Line Metro stations, remains the foremost TOD example in this region. Metro stations are the anchors for TOD strategies and tactics guiding the multi-decade makeover of Tysons in Fairfax County; redevelopment of White Flint, Twinbrook and Wheaton in Montgomery County; and planning for New Carollton in Prince George’s County.

[Why — and at what stations — Metro expects ridership to grow]

Transit-oriented development is driven in part by real estate market forces and changing demographics. Studies show  that single-person households are now the most common household type, and that young adults as well as seniors prefer living in pedestrian-oriented, urban-style communities served by transit. Thus, several key attributes typify and characterize transit-oriented development.

Proximity and accessible transit: Being linked to rail stations or bus rapid transit (BRT) stops is the essence of TOD-Intensified development around or near transit nodes is above all intended to modify travel behavior of home owners, tenants, shoppers and workers. It enables and motivates increased use of transit, ownership of one less car or no car, reduced traffic congestion and pollution and more walking and biking.

TOD does even more. It benefits the health of residents. And it increases wealth, since owning one car or no car, using transit and driving less lowers household expenses. By contributing to increased transit ridership, it also augments much-needed transit system revenue.

Multi-modal travel networks: TOD plans invariably call for creation of a rationally configured, interconnected, internal network of streets and pathways serving vehicles, pedestrians and bicycle riders. Such networks must encompass transit nodes or connect to external streets and safe, attractive walkways leading to transit nodes. Providing pedestrian connectivity to the transit network is essential for encouraging transit use.

Higher density and mixed uses: TOD always embodies increased density — more and higher buildings — and a wide range of building types and uses. Virtually every TOD includes commercial office space, housing — apartments and townhouses — and street-level retail and restaurant space.

Sometimes added to the mix are cultural, recreational, educational and health-care facilities, perhaps a civic center or hotel. Usually a number of developers and various architects are involved. Most jurisdictions require that a portion of all new TOD housing — 12 percent, for example — be available at below-market-rates and affordable for households earning less than a stipulated percentage of the jurisdiction’s median income.

To some extent, this helps address the Washington area housing affordability challenge but does little for most of the thousands of households at the bottom of the income pyramid.

Somewhat diverse demographics: Higher density and mixed use theoretically suggest substantial demographic diversity within TOD residential projects. Transit-oriented developments tend to attract millennials, couples of any age and empty-nesters, all attracted to and able to afford the TOD lifestyle.

But TOD neighborhoods generally lack two notable population segments: families with school-age children for whom TOD apartments are too small and who prefer school-centered communities; and low-wage members of the workforce, who normally can’t afford the rents or selling prices of TOD  units.

Parking garages replacing surface lots: Achieving higher TOD density often entails building on surface parking lots, in turn necessitating structured parking either below buildings or in above-grade garages. But increased density is what makes structured parking economically feasible, although not inexpensive. TOD obliges real estate developers and financial backers, along with public sector planners and zoning regulators, to rethink and reduce existing parking requirements.

[Metro advances project to transform New Carrollton]

Yet right-sizing TOD parking structures entails at best making intelligent guesses. No formulas or reliable statistics exist to predict future TOD parking needs, which are expected to diminish as car ownership goes down and use of transit goes up.

Parks, gardens and playgrounds: Every TOD includes a network of diverse public and private open spaces complementing the TOD network of movement and related buildings. Some landscaped open spaces may be passive, informal and intimate while others are active, formal or grand in scale. Again, higher density and taller structures enable creation of more meaningful, functional, attractive open space.

Transit-oriented development will not address and solve all problems facing this metropolitan region, especially the shortage of affordable housing, but it will make it more cosmopolitan.

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