Housing people, businesses and other functions also entails housing cars. But in the future how many cars will we really need, and where should we park them?

Parking inevitably sparks debate about sustainable smart-growth proposals characterized by high density, mixed uses, more affordable housing and diverse mobility choices — walking, transit, biking — in addition to driving cars.

For growing cities and counties experiencing significant redevelopment and new development, especially transit-oriented development, parking is a hot-button issue. Americans love cars and want to park them as close as possible to where they live, work, shop, recreate and pursue entertainment.

But crafting public policy and future regulations for parking is a daunting challenge. Realistic parking space needs associated with property development can vary substantially depending not only on type of land use, but even more so on property location, transportation options and automotive behavior.

An office or apartment building next to a subway station clearly needs less on-site parking than these same buildings situated two miles from a subway station. Likewise, retail or cultural destinations adjacent to transit require less parking than those inconveniently far from transit.

(Roger K. Lewis)

On-site parking needs for a property are affected by the availability and amount of on-street parking. And parking needs associated with housing decrease substantially when residents choose to own only one car or to rely entirely on short-term rental cars.

Variability in parking needs is exemplified by Washington’s 14th Street NW, north of the Logan Circle area. Transformed dramatically in recent years, the 14th Street corridor has become a 21st-century model of desirable urban renewal. The corridor has been invigorated by new restaurants and cafes, new shops and stores, and new or renovated apartment and office buildings. With the Studio Theatre and Whole Foods store as anchoring destinations, the neighborhood around 14th and P hums with activity around the clock.

Yet greatly increased restaurant, retail, commercial and residential development has not been accompanied by a corresponding increase in parking everywhere it’s needed. In particular, along 14th Street for several blocks north of P, public parking is a scarce and expensive commodity.

Moreover, the nearest Red Line and Green Line Metro stations are a half mile or more away, just far enough to be a challenging walk for older folks, for people with disabilities and for parents with very young children in tow. Bad weather makes walking to and from stations even more problematic.

But the parking situation is quite different a mile north in the redeveloped Columbia Heights neighborhood. Its Green Line Metro station on 14th Street is steps away from the multi-story retail edifice housing several spacious stores, including Target. Below this building is a multi-level, public parking garage that is never filled to capacity.

Columbia Heights street network congestion undoubtedly motivates people in the surrounding neighborhoods to walk to Columbia Heights destinations rather than driving and parking, which helps ensure that the garage is never full. Likewise, people from more distant neighborhoods probably choose not to drive, instead coming to Columbia Heights via Metro for shopping, dining or working.

The parking imbalance in the 14th Street corridor could be remedied by building a multi-level parking structure on city-owned property between 14th and 13th streets, a few blocks north of P Street. Either the city or a parking garage operator could construct and manage the garage, which would be self-financing. From such a garage, people could comfortably walk or hop on a local shuttle to reach their destinations.

This remedy would be an urban version in reverse of Metro’s suburban parking strategy, whereby Metro commuters drive to large parking garages at suburban Metro stations around the region. It also would emulate Montgomery County’s practice of building public parking garages embedded within the county’s urban nodes.

A one-size-fits-all zoning approach to accommodating parking doesn’t work. Yet this is how conventional ordinances have been written. Minimum, immutable on-site parking requirements are stipulated as a ratio for each type of use: number of on-site parking spaces per house or apartment; or one parking space per predetermined increment of net usable floor area. Or no on-site parking is required, as along 14th Street.

A fine-grained, flexible, less formulaic planning methodology is necessary to realistically predict and regulate parking. The methodology must take into account not only a wide range of variables, but also highly site-specific variables. It must allow for regulatory judgment and discretion based on contextual circumstances and needs. And it must include public parking garage construction at key locations as part of the smart-growth tool kit.

Changing policies, methodologies and regulatory approaches to better distribute parking spaces will have a positive economic impact. A structured parking space today costs tens of thousands of dollars to build. This cost is passed on to buyers, tenants, clients and customers. Parking is never free. Thus, constructing no more parking spaces than needed lowers development costs and directly benefits consumers as well as developers.

Two other potential benefits can accrue. Parking cars in well-designed, wisely located garages gets rid of unsightly surface parking lots, a desirable aesthetic enhancement. And eliminating pollutant-filled stormwater running off surface parking lots enhances environmental quality.

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