Parking lots amplify high temperatures. Why are we still requiring them to be larger than they need to be?

Urban heat islands got national attention this past summer after a record heat wave in the Pacific Northwest killed hundreds. In Portland, where the heat disparities between neighborhoods are among the worst in the country, one thing jumps out when you look at maps of these places: huge parking lots.

When agencies publish guidance for how to break up heat islands, they usually suggest shady trees and lighter-colored roads. But one assumption goes relatively unquestioned: why do we have these huge parking lots in the first place?

“People don’t want to go there because they’re afraid of the blowback or something,”

said Ted Labbe, a Portland-based habitat advocate who helped found the group Depave. In his experience, public officials will often talk about adding trees and rain gardens, but they never start by asking how much parking is really needed.

“Pavement removal is the simplest, lowest-cost, lowest-maintenance intervention you can do,”

said Labbe, but

“surprisingly, pavement removal is not considered a best practice.”

HOW ONE ZONING DECISION TRANSFORMED A NEIGHBORHOOD

Large parking lots are not natural or inevitable. They do not spontaneously appear, like dandelions on the edges of roads. They are the outcome of a series of choices by property owners and the governments that regulate these owners. And those choices have consequences.

Sightline took a deep dive into one of the hottest areas of Portland: Southeast 82nd Avenue and Foster Road, the western anchor of the Lents neighborhood, marked off by the black rectangle in the map below. This area was largely redeveloped after Portland added its first parking requirements in its 1959 zoning code. The new code defined minimum off-street parking ratios for more than 50 types of businesses, from bowling alleys (two parking spaces per lane) to wedding chapels (one parking space per 56 square feet of public floor area).

Parking requirements are based on little or no data. Yet Portland joined in the mid-twentieth century car-centric planning craze that was sweeping the nation. According to urban planning scholar Donald Shoup in The High Cost of Free Parking, a survey of 76 cities in 1946 found that only 17 percent of them had parking requirements in their zoning code. Five years later, 71 percent had adopted them or were in the process of doing so. “Other than zoning itself, few if any other planning practices have spread more rapidly,” wrote Shoup.

Off-street parking in Lents did exist before the minimum requirements went into effect, but the new rules cast those norms in stone. Once new buildings were required to supply enough on-site parking for anyone who showed up in a car, the price that car owners would ever be willing to pay for parking in the area fell to zero. It also became pointless for a new building even to share its parking lot with a neighbor; after all, it was already required to create its own dedicated lot.

Even then, big parking lots weren’t the only way to do business. Businesses on the triangular block between SE Foster and SE Harold still operate in buildings constructed between 1911 and 1950. Today, multiple businesses share the parking lot, which equates to 1 parking space per 1,000 square feet of building area.

But since 1959, parking mandates for new construction kicked off a cycle in which people expected more and more parking. The red-outlined area in the map below, which was redeveloped after parking minimums went into effect, has 3 parking spaces per 1,000 square feet. By 1970, new big box stores were providing 4–5 spaces per 1,000 square feet, above and beyond what was required.

Even way back in a 1954 Planning Advisory Service report on shopping center design, Architect G. Morton Wolfe wrote about the pressure to expand parking lots. “Many years ago it was considered good practice to provide as much parking area as the total area of the bui...