PHILADELPHIA — Cities across the United States are struggling with a common problem.

No, not the economy. (Although that’s a good guess.)

It’s the car.

In the last 50 years, American cities have embraced the private car with abandon, constructing highways and byways that encircled them, divided them and changed their very nature forever.

Make no mistake; the car and the infrastructure to support it has been tremendously helpful. It is impossible to think of driving through a town as dense as New York or as sprawling as Los Angeles without multi-lane express roads. You’d have to clear your schedule for the day just to make it from one end to the other.

But it’s the “with abandon” part that’s the problem. Cars are part of the solution, yes, but they are not the only solution. And that’s precisely the challenge city officials face today as they attempt to develop vibrant cities in the face of generations-old car culture, according to Next American City editor at large Diana Lind.

“They’re responding to urban highways,” she said. “Cities are finding ways to knit urban fabric back together.”

Speaking at the second annual TEDxPhilly conference on Tuesday, Lind listed several American cities that were working to balance the transportation ratio.

Among them:

• Denver, where a light rail partnership changes the dynamic from suburban sprawl to transit-oriented development.
• Washington, D.C., where the “Circulator” bus offers easy transport to the city’s array of downtown attractions.
• New York City, where thousands of miles of bicycle lanes and select no-auto zones have “done a lot to prioritize the pedestrian.”
• Cleveland, where officials took over a parking structure for cultural events and seek to tear down a highway that blocks the waterfront.
• Dallas, where the Woodall Rodgers Deck Park mitigates a major freeway dividing the city’s downtown and uptown districts.
• New Haven, where an elevated highway is being dismantled in favor of a level boulevard.
• Providence, where a highway was moved and replaced with the WaterFire public art project and an economic opportunity zone for technology startups. “They realized that having a highway in the middle of downtown is actually a huge waste of space,” Lind said.
• Oklahoma City, where the aging Crosstown Expressway was dismantled in favor of a park.
• Portland, Ore., where city officials have redirected funds meant for the Mount Hood Freeway to the MAX Light Rail system.

“They are realizing that it’s no longer environmentally sustainable to have so many people driving,” Lind said — not just in terms of emissions, but in terms of traffic and balancing multiple modes of transportation.

In a time of economic distress, it makes even more sense, Lind said. The average car owner spends $8,000 a year on his or her vehicle; that money doesn’t flow into the local economy.

For a city like Philadelphia, where Lind lives and where half the population has a household income of $35,000 or less, that’s unacceptable.

The solution? Take advantage of the lifecycle of aging infrastructure and, when sections of highways are due to be rebuilt, rethink the need for them in the first place.

“Have we learned nothing from our mistakes in the past?” she asked. “Do we have no ideas for the future of our city?”

It’s been done before. After the 1989 Loma Prieta earthquake, the city of San Francisco faced the tremendous task of rebuilding the structurally-damaged Embarcadero Freeway. Instead, they tore it down, replaced it with a people-friendly boulevard that encouraged development. The surrounding area has since rebounded, Lind said, with higher property values, more tourism and more housing for city residents.

The same phenomenon occurred in New York City when it rebuilt the elevated West Side Highway in 1989 as a surface roadway, giving New Yorkers access to parks, piers and picturesque views on the West Side of Manhattan.

So why not replace Philadelphia’s aging Interstate 95, which blocks much of the city’s access to the Delaware River, when its lifespan is exhausted? All 51 miles of Philly’s section of I-95 are in phases of structural obsolescence, Lind said, and it’s almost surely better to encourage industry, education and the public to reclaim the waterfront.

“Instead of reverting, we should try something that reflects the direction the country is going in,” Lind said. “So that in 2026, when it’s the 250th anniversary of the Declaration of Independence, we are creating a city that will last another 250 years.”