Susan Alexander, left, brings passengers Mary and Al Liepold to Reagan National Airport. All three are members of the Silver Spring Time Bank. (Justin Wm. Moyer/The Washington Post)

On a recent spring morning, Susan Alexander left her Maryland home, climbed into her Volkswagen Passat and drove about three miles to pick up two strangers. She battled rush-hour traffic on the Capital Beltway and George Washington Memorial Parkway before dropping them off curbside at Reagan National Airport.

She didn’t earn a dime for her trouble, and that was the point.

There and back, the trip took about 90 minutes — worth about $40 if Alexander, a retired government intelligence analyst, were an Uber driver. Instead, she’s a member of the Silver Spring Time Bank — one of more than 100 such exchanges around the world trying to build community by exchanging time credits for services instead of dollars and cents.

“I have time,” she said. “I like giving the gift of time to other people.”

Though some communities have experimented with local currency, most time banks offer an alternative, powered by 21st-century technology, to the U.S. dollar. About 70 exist across the country — some with a few members, others with hundreds — to give value to work that members say often goes uncompensated in a traditional market economy.

In Alexander’s case, passengers Mary and Al Liepold were grateful for the ride, but it wasn’t charity. Mary, a retired writer and editor for nonprofit organizations, used time credits she banked for editing work and baking. Senior citizens who don’t drive, the Liepolds cashed in their credits to catch a flight to Montreal for a five-day vacation.

Without money changing hands or shifting between virtual accounts, the airport drop-off was more like a coffee klatch than a taxi ride. Driver and passengers chatted about projects they’ve completed for the time bank, and no one raised an eyebrow when Mary said she likes “to avoid the conventional economy.”

“The beauty of this is that you make friends,” Mary Liepold said. “You don’t just get services.”

The Silver Spring Time Bank formed in 2015 and has about 300 members, said co-founder Mary Murphy. Last year, she said, 1,000 hours were exchanged for basic home repairs, dog walking, cooking and tailoring, among other services, without the exchange of money.

“You get to save that money that you would have spent,” she said. “You get to meet somebody else in your community and get to know that person. That’s a bonus that’s part of an exchange.”

A transaction performed partly to make friends would seem to go against classical economics and one of Benjamin Franklin’s most memorable chestnuts: “Time is money.” To those at the forefront of modern time-banking, that’s the appeal.

Edgar S. Cahn, an 84-year-old law professor at the University of the District of Columbia who had worked on civil rights and anti-poverty legislation in president Lyndon B. Johnson’s Justice Department, suffered a heart attack in 1980. He said doctors gave him two years to live, with “maybe two good hours a day.”

“I thought: What do I do with two good hours a day?” he said, having beaten doctors’ expectations by nearly four decades. “I have to teach people to value themselves.”

Cahn became a proselytizer for what he called the “time dollar” — a currency in which an hour of work is worth an hour of work, whether it’s performed by a maid, a mechanic or a mechanical engineer. In 1995, he founded the D.C. nonprofit TimeBanks USA, which developed the software used by many time banks around the world. (The organization charges time banks a one-time $79 start-up fee in actual dollars for the software, and additional fees of about $3 per member each year.)

Cahn said worthy services are routinely completed with no compensation in the market economy, pointing to a 2014 RAND Corporation study that valued informal caregiving for elderly Americans at more than $500 billion a year. Using time as currency “values what it means to be a human,” he said.

“We’re all trained as human service professionals: ‘How can I help you?’ ” he said. “None of us is trained to say: ‘How can you make a difference?’ I need you as much as you need me.”

While the world is unlikely to shift to an international time credit economy, hours have been exchanged in time banks in at least seven countries, including South Korea, New Zealand and France, according to the TimeBanks USA website.

One of the most-active time banks in the United States is the Crooked River Alliance of Timebanks, based in Kent, Ohio. Started in 2010, the alliance has 1,200 members in five branches that have facilitated more than 70,000 hours of exchanges, according to Abby Greer, its founder and director.

“I’m the Bill Gates of time banks,” she said.

Greer said time banks can serve as small-business incubators and a way for seniors to remain active after retirement. They also put value on work that’s not traditionally compensated, like homemaking, she said.

“Everyone’s time is equal,” Greer said. “It changes your thinking about money, wealth, community and knowing your neighbors. All these things have been lost in the past 100 years. The time bank is bringing them back.”

Time banks have also saved their members money.

Alexander, who shuttled the Liepolds to the airport, was giving back after recently spending her time credits to have her home thermostat replaced. She estimated an electrician would charge more than $100 for the job, but fellow timebanker Don Slater, a former NASA engineer turned National Oceanic and Atmospheric Administration contractor, finished the job in about 30 minutes.

Despite his credentials, Slater, 68, called the wage differential between lower-paid jobs and jobs like his former one “ridiculous.”

“We train for different things, we follow different paths,” he said. “While one may be much more visible than the other — more stressful than the other — it doesn’t make it any less important or less significant.”

As Alexander drove 12 miles back home to Takoma Park, Md., after dropping off the Liepolds, she said the trip wasn’t about profit margins, but the promise of future contact.

“It was funny — we hugged goodbye,” she said. “I’ve never met these people before, but it feels like we’re part of the same family.”

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