Americans care a whole lot about parking. Which is why the same questions arise when new master plans, new zoning provisions and new real estate projects are proposed: How much parking really will be needed in the future, when will it be available and where should it be located?

The answers do not come easily.

Counties and municipalities must juggle many factors when adopting new parking policies and standards. And controversy is inevitable whenever planners envision future parking requirements less stringent than those of the past. Thus, much of the challenge is justifying changes to existing standards.

For each type of land use within a jurisdiction, zoning ordinances typically dictate minimum on-site parking requirements. These usually are specified as ratios: number of parking spaces relative to occupiable square feet within a retail or commercial building — for example, one space for every 1,000 square feet; or number of spaces per dwelling unit in a residential building.

As if zoning weren’t enough, lending institutions seek to further protect their real estate investments by insisting that developers provide enough parking to satisfy what they perceive to be consumer and tenant expectations. Sometimes lenders’ requirements even exceed zoning requirements.

Typically formulaic, one-size-fits-all minimum parking ratios are based on generalized, long-standing assumptions about parking needs and, in the case of commercial real estate, predictions of probable peak demand. Many of these decades-old assumptions are becoming invalid.

Yet predicting parking demand in decades to come is both a challenge and an opportunity. Future development based on “smart growth” principles will change travel attitudes and habits. More telecommuting, teleconferencing and Internet shopping, along with skyrocketing fuel costs, likewise will affect travel behavior. These changes will lead to reduced parking demand while providing environmental and health benefits.

More high-density, mixed-use, transit-oriented development (TOD) in cities and suburbs will produce walkable neighborhoods and districts. As an alternative to driving, people will be able to get around conveniently on foot and on bicycles, or ride buses, streetcars or trains. This means fewer parking spaces, even in places like Tysons Corner.

Another issue is the true cost of constructing parking. For a structured parking garage, the costs of excavation, foundations, walls, ramps, driving aisles, lighting and safety systems for ventilation and suppression of fire and smoke can cost $30,000 to $40,000 per space. And costs will keep rising. These costs must be fully paid by parking space users — building tenants, workers, visitors, shoppers, housing residents — or be subsidized using public-sector funds. But cities and counties cannot afford to continue subsidizing parking, especially when funds would be better spent supporting transit options.

Combining high density and diverse uses — commercial and residential in particular — reduces parking demand for another reason. Parking for workers in office buildings is most needed during weekdays and much less on weekends. Retailers need parking for customers during weekday lunchtimes and Saturdays. Residents and their guests need parking spaces mostly at night and on weekends.

Zoning regulators traditionally calculated total parking spaces required within large developments by adding up the spaces required separately for each type of use, as if each use existed alone. But when dense, diverse uses coexist, some parking spaces can be shared, thereby serving double-duty and lowering total demand. Ride-sharing can lower the demand even more.

Smarter development, coupled with proactive parking demand management, is more healthful because it encourages people to get more exercise. By replacing sprawling, on-grade parking lots, it is also environmentally healthier. Stormwater running off thousands of acres of impervious parking lot surfaces is a major source of chemicals and particulate matter polluting the region’s streams and rivers, and ultimately the Chesapeake Bay.

Of course, a surface parking lot is by far the cheapest form of parking to build, with each space costing a small fraction of the expenditure of a space in a structured parking garage. This is why it is financially impractical to build multi-level parking garages serving low-density, low-rise suburban or exurban real estate. Whether underground or above-ground, parking garages make economic sense only in high-density developments.

Anticipating and planning for future growth, jurisdictions crafting new master plans and land use regulations recognize that business-as-usual parking standards ultimately will prove wasteful and expensive. To encourage more walking and less driving, some cities and counties are even considering stipulating maximum rather than minimum allowable parking spaces, especially in locations well served by transit. They realize that such fine-grain planning and regulation are necessary because actual parking needs vary from site to site, that one-size-fits-all parking requirements no longer make sense.

Whatever public policy and regulatory choices are made in the jurisdiction where you live, one thing is clear. Both the opportunities and incentives not to drive and not to pay for parking will increase. Consequently, it’s not too soon to start looking for some good walking shoes.

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