A sign on a parking meter in Arlington. (John Kelly/The Washington Post)

Each week, In Theory takes on a big idea in the news and explores it from a range of perspectives. This week, we’re talking about car-free cities. Need a primer? Catch up here.

Donald Shoup is a professor in the department of urban planning in the Luskin School of Public Affairs at University of California, Los Angeles.

For most of the past century, all our cities have been built to suit the car. Other than historical anomalies like Venice, it remains unlikely that we will see any carless cities soon. Nevertheless, speculating about carless cities can help to show the benefits of having fewer cars and parking spaces.

Because cities with fewer cars will need fewer parking spaces, city planners can abandon their most expensive zoning regulation: off-street parking requirements. Requiring all new buildings to provide ample off-street parking spreads the city over a larger area, reduces density and makes cars the default way to travel. Parking requirements also undermine public transit and make life harder for people who are too poor to own a car.

I argue in “The High Cost of Free Parking” that minimum parking requirements subsidize cars, increase traffic congestion and carbon emissions, pollute the air and water, encourage sprawl, raise housing costs, exclude poor people, degrade urban design, reduce walkability and damage the economy. To my knowledge, no city planner has argued that parking requirements do not have these harmful effects. Instead, a flood of recent research has shown that parking requirements have these effects and more. We are poisoning our cities with too much parking.

Parking requirements reduce the cost of owning a car but raise the cost of everything else. For example, parking requirements raise the price of food at a grocery store for everyone regardless of how one travels. People who are too poor to own a car pay more for their groceries to ensure that richer people can park free when they drive to the store.

Cities require parking for every building without considering how the required spaces place a heavy burden on the poor. A single parking space, in fact, can cost far more to build than the net worth of many American households. In recent research, I estimated that the average construction cost (excluding land cost) for parking structures in 12 American cities in 2012 was $24,000 per space for aboveground parking and $34,000 per space for underground parking. By comparison, the median net worth (the value of assets minus debts) was $7,700 for Hispanic households and $6,300 for black households in the United States, based on data from the U.S. Census Bureau, in 2011.

One required space in a parking structure therefore costs at least three times the net worth of more than half of all Hispanic and black households in the country. Nevertheless, cities require several parking spaces per household by imposing parking requirements at home, work, stores, restaurants, churches, schools and everywhere else.

Many families have a negative net worth because their debts exceed their assets: 18 percent of all households, 29 percent of Hispanic households and 34 percent of black households had zero or negative net worth in 2011. The only way these indebted people can use the required parking spaces is to rent or buy a car, which they often must finance at a high, subprime interest rate. In a misguided attempt to provide free parking for everyone, cities have created a serious economic injustice by forcing developers to build parking spaces that many people can ill afford.

City planners cannot do much to counter the inequality of wealth in the United States, but they can help to reform parking requirements that place heavy burdens on minorities and the poor. Removing minimum parking requirements may be the cheapest and simplest way to achieve a more just society, and will produce a cascade of benefits for cities, the economy and the environment. Best of all, cities don’t need to wait until cars disappear before they remove their unwise parking requirements. They can remove their parking requirements now.

Explore these other perspectives:

J.H. Crawford: The car century was a mistake. It’s time to move on.

Randal O’Toole: Transit is dead. Let’s prepare for the next mobility revolution.

Shivani Radhakrishnan: How jaywalking became a crime

Jarrett Walker: Why cars and cities are a bad match

Aaron Renn: Self-driving cars will change more than just traffic. Here’s why.