Martin Gerstell treasures his Thursday morning volunteer stint at the National Gallery of Art, where he fields questions at the main information desk. He patiently responds when visitors ask about the current exhibits, whether the paintings are real, where the bathrooms are.
Usually, fellow volunteers give him a ride from his assisted living residence in northwest Washington to the museum downtown, and home again. But when they can’t, Mr. Gerstell, 94, uses the Uber app his granddaughter installed on his iPhone.
“They appear very quickly, and they’re very helpful,” Mr. Gerstell said of his Uber drivers, who fold and stash

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