Indoor shopping malls often are mobbed and their parking lots full during this holiday season, yet the viability of some malls and mall architecture seems in doubt. Recently, The Washington Post reported on plans to eventually demolish the White Flint shopping center on Rockville Pike in Montgomery County and completely redevelop its site. In the past few years, only a couple of large enclosed malls have been proposed in the United States. Meanwhile, many malls and shopping centers are falling on hard times, some of them falling apart.

What explains these trends? Are people’s shopping needs and habits changing? Are national economic conditions or competition from Internet sites the cause? Perhaps national retail chains and retail real estate developers, in an attempt to stimulate market demand, are cooking up alternative design formulas just for the sake of novelty.

In many locations, the enclosed shopping mall seems to be giving way to the popular “town center” concept, which seeks to create a pedestrian-friendly, outdoor environment with animated streetscapes and citylike, street-block patterns. Some town centers, like Bowie Town Center, have been built from scratch, while others have been created through the successful redevelopment of buildings and neighborhoods, including Bethesda Row in Montgomery County and Shirlington in Arlington County.

Larger stores can exist within the fabric of a retail town center, but big-box and department stores must usually remain peripheral, if they are present at all. Town centers also can be made denser and encompass other uses — offices and housing — above or alongside retail uses. Town centers’ parking garages and surface lots are generally embedded within block interiors and behind stores instead of facing streets in front of stores.

Of course, many new town center developments are occupied by the same national chain stores and franchises that are in conventional enclosed malls. Indeed, the town center’s retailing formula generates the same challenge as the old enclosed shopping mall formula: Rents typically are too high and unaffordable for most locally owned, community-oriented shops and stores. This problem also arises when older buildings are repurposed and modernized to include upgraded or new street-facing retail space.

Retail architectural paradigm shifts are not the result of developers and retailers merely deciding to try something different. Rather, these shifts are a response to social, demographic, cultural and geographic changes that are an integral part of changing American history.

After World War II, the enclosed regional shopping mall emerged because of two interdependent American phenomena: construction of the interstate highway system and rapid growth of low-density metropolitan suburbs.

Starting in the early 1950s, residents and many businesses fled cities, populating the expanding outer suburbs. Downtown department stores and smaller shops had ever fewer customers, but suburbanites still needed a place to shop, and the regional shopping center satisfied that need perfectly.

With affordable cars, cheap gas, a growing network of arterial roads and a seemingly endless supply of inexpensive land, the regional shopping mall was a logical invention. Equally logical was the real estate and mall design formula: acquire land with access to a major highway; assemble enough acreage to build a very large, weatherproof structure surrounded by parking lots; construct long concourses (often two levels high) lined on each side by scores of shops; and plug the ends of concourses with anchor department stores. To complete and enhance the formulaic picture, provide a food court, pump up concourse light levels, design enticing storefronts, pipe in music and pleasant scents, and install seasonal decorations, including Santa Claus.

This formula proved extremely successful throughout America.

Today, however, middle-class flight from cities has ebbed. Adult children of the generations that inhabited post-war suburbia often choose not to stay in the the suburban settings where they grew up. Even their parents, tired of maintaining a house bigger than they now need, are heading back toward or into cities. Others (the young, middle-aged or elderly) are choosing to live in denser, walkable communities, where there is more to do and where shopping does not require driving several miles. This is one reason why town centers are being built, even in suburban locations, and why huge shopping malls are not.

Traditional nuclear families (mother, father, two kids) are now less than half of all American households. Coupled with falling home values, mortgage foreclosures and unemployment, demographic reality is contributing to the depopulation of many suburban and exurban communities. A shopping mall cannot survive without population growth and customers who can afford to shop.

Also, for essentially aesthetic reasons, more people prefer not to shop in fading, older retail facilities that may be poorly maintained and perhaps half-empty. This suggests that Americans’ taste and appreciation of good architecture is improving.

Of course, many enclosed shopping malls are not in jeopardy. Because of strategic location, better design, a healthy mix of retail tenants and tributary market stability, many existing malls will remain successful.

Some mall sites will undergo intense redevelopment, such as that planned for the Columbia, Md., regional shopping mall and surrounding property. Howard County has approved a plan and zoning for a radical transformation of Columbia’s “downtown,” centered on the mall. Plans envision a new street-block pattern, mixed uses, higher density, taller buildings and thousands of new housing units.

Like Columbia’s mall, Tysons Corner’s two shopping malls aren’t going away anytime soon. But Fairfax County’s plan for Tysons will urbanize the malls’ unattractive, dysfunctional suburban environment. Finally, in a citylike Tysons Corner, shoppers will be able to walk safely between retail destinations.

Roger K. Lewis is a practicing architect and a professor emeritus of architecture at the University of Maryland.