Charlottesville zoning officer Craig Fabio pedaled into a driveway on River Street and peered inside a stack of tires. “No rims,” he said, pulling out his cellphone to photograph the evidence. “It’s a violation. Breeds mosquitoes.”

If Fabio had been driving a car, he might have sped past the tire pile without seeing it; and if he had seen it, he couldn’t have investigated until he found a place to park. Instead, he was riding an electric-assist bicycle, using both pedal power and its battery-operated motor to cruise at a practical 10 to 15 mph. His $1,800 Giant Twist Freedom model is one of two e-bikes the city provides to its zoning officers to increase efficiency while diminishing congestion and greenhouse-gas emissions.

Popular elsewhere in the world — about 20 million a year are sold in China, where they are licensed and regulated like cars — e-bikes are slowly gaining ground in the U.S. market. Some buyers like their green credentials; Charlottesville bought its e-bikes after signing the U.S. Conference of Mayors Climate Protection Agreement. (The city considered Segways, but e-bikes were cheaper and allowed officers to get across town almost as quickly as they could by driving.)

Others see them as an ideal commuter vehicle, because they allow the rider to work as hard as he or she wants — typically, that means using the electric motor to help out on the ride to the office and switching to pedal power for a workout on the way home.

The typical e-bike has a mountain-bike-style frame, with a motor located inside an unusually large rear hub and a lithium-ion battery pack, usually mounted on a back rack. The switch between pedals and battery differs depending on the model: Some can be ridden on pure battery power; others, including the Twist Freedom, made by Giant Bicycle, are “pedal assisted,” meaning the electric boost kicks in only if the rider is pedaling.

Depending on how much the rider pedals, a typical five-hour charge will last for about 40 miles — and if the batteries die, the 50-pound e-bike can usually be pedaled (or walked) home.

Young and older

David Goodman had never heard of e-bikes until he dropped into the Green Commuter bike shop in Takoma Park last year to pick up some saddle bags. But the 33-year-old anesthesiologist walked out of the store with an electric-assist Europa that would give him “help up the hill” on his three-mile commute to Holy Cross Hospital.

“I saw it and realized it’s great that there is something to help with the pedaling, something that would make my commute sweatless,” he said. “I let people at the hospital try the Europa out, and there’s always a smile on their face when they’re done riding. For me, it’s all about the fun factor and the easy way to get some exercise.”

Joe Reyes, who owns the bike shop, said he sells two or three e-bikes a month, mostly to commuting professionals such asGoodman.

“One customer calculated that on his $1,400 e-bike, in Metro savings he’ll pay for it in a year, and he doesn’t add in the exercise element,” Reyes said. “You’re providing about 75 percent of the power, so you’re still getting some exercise. . . . You don’t have to get to work all sweaty, and then on the way home you don’t have to use the electric assist, but it’s always there on tap if you need it.”

The bikes are also drawing attention from an older crowd.

“By far, our number one market is baby boomers who are out of shape, just got out of surgery or for some other reason are just getting back on the bike,” says engineer Jason Seybold, a founder of E+ Electric Bikes, a high-end e-bike manufacturer in Dulles. The company has a small showroom where customers can get a look at its line of nine bikes, which start at $2,500 and are notable for having the battery installed inside a hub. The company’s choices include an Emergency Medical Services model: Equipped with a bag big enough to hold a paramedic’s equipment, it’s meant to be used at large outdoor events, where medical staff might need to maneuver quickly through crowds.

Two years ago, Lionel and Claire Metz bought e-bikes for use around their home in Albemarle County, Virginia. Lionel, 87, values the moderate outdoor exercise it provides, something he needs after three years of medical problems that included prostate surgery. Claire, 63, said that she rarely misses a day on her e-bike, often cruising a 20-mile loop.

“There’s a library full of research on the benefits of movement,” Colin Milner, chief executive of the International Council on Active Aging, says. “So a product like this would certainly accommodate someone who has issues with their joints, or is overweight, or has other health issues. It’s a good beginning.”

Salzman is a Charlottesville writer specializing in alternative transportation and related issues.