On a Thursday evening in late June, Clarissa Champlain learned that her 15-year-old son Brodee had been in a terrible crash, the latest teen victim of an e-bike accident.

He had been riding from home to shot-putting practice. The e-bike, a model made by Rad Power, had a top speed of 20 miles per hour, but his route took him on a busy road with a 55-mile-per-hour limit. While turning left, he was clipped by a Nissan van and thrown violently.

Ms. Champlain rushed to the hospital and was taken to Brodee’s room. She could see the marks left by the chin strap of his bike helmet. “I went to grab his head and kiss him,” she recalled. “But there was no back of his head. It wasn’t the skull, it was just mush.”

Three days later, another teenage boy was taken to the same hospital after the e-bike he was riding collided with a car, leaving him sprawled beneath a BMW, hurt but alive. In the days following, the town of Encinitas, where both incidents occurred, declared a state of emergency for e-bike safety.

The e-bike industry is booming, but the summer of 2023 has brought sharp questions about how safe e-bikes are, especially for teenagers. Many e-bikes can exceed the 20-mile-per-hour speed limit that is legal for teenagers in most states; some can go 70 miles an hour. But even when ridden at legal speeds, there are risks, especially for young, inexperienced riders merging into traffic with cars.

“The speed they are going is too fast for sidewalks, but it’s too slow to be in traffic,” said Jeremy Collis, a sergeant at the North Coastal Station of the San Diego County Sheriff’s Office, which is investigating Brodee’s accident.

To some policymakers and law enforcement officials, the technology has far outpaced existing laws, regulations and safety guidelines. Police and industry officials charge that some companies appear to knowingly sell products that can easily evade speed limits and endanger young riders.

“It’s not like a bicycle,” Sergeant Collis said. “But the laws are treating it like any bicycle.”

Two federal agencies, the Consumer Product Safety Commission, and the National Highway Traffic Safety Administration, said they were evaluating “how best to oversee the safety of e-bikes,” according to a statement provided by the highway safety agency.

Communities have begun to alert their residents to the dangers of e-bikes. In June, the police department in Bend, Ore., ran a public service campaign acquainting the public with the e-bike laws that were frequently being broken there. Days later, a 15-year-old boy was killed when the e-bike he was riding was struck by a van.

Sheila Miller, who is the spokeswoman for the Bend police and helped develop the public service campaign, emphasized that not everything that calls itself an e-bike qualifies as one, or is safe or legal for minors. Under Oregon law, which is more restrictive than those in most states, a person must be at least 16 to ride an e-bike of any kind.

“Parents, please don’t buy these bikes for kids when they are not legally allowed to ride them,” Ms. Miller said. “And if you own an e-bike, make sure that everyone who is using them knows the rules of the road.”

Booming Industry, Modest Regulation

The typical e-bike has functioning pedals as well as a motor that is recharged with an electrical cord; the pedals and the motor can be used individually or simultaneously. Unlike a combustion engine, an electric motor can accelerate instantly, which makes e-bikes appealing to ride.

E-bikes are also seen as vital in shifting the transportation system away from emission-spewing cars and the congestion they create, said Rachel Hultin, the policy and governmental affairs director for Bicycle Colorado, a nonprofit advocacy group for bicycle safety and policy. E-bikes and electric scooters are part of the so-called micromobility movement, propelling commuters and other people short distances across crowded spaces.

The number of e-bikes being sold is unclear because, like regular bikes, they do not need to be registered with the government. (Cars, motorcycles and mopeds must be registered through a state’s Department of Motor Vehicles.) Many are sold directly to consumers over the internet, rather than through physical retailers that often track sales. John MacArthur, an e-bike industry expert with the Transportation Research and Education Center at Portland State University, estimated that roughly one million e-bikes would be sold in the United States this year.

The minimal regulation around e-bikes is a selling point for the industry. Super73, a company in Irvine, Calif., that makes popular models, advertises on its website: “RIDE WITHOUT RESTRICTIONS. No license, registration, or insurance required.”

“It’s one of the very unique categories of vehicle that there really isn’t any kind of onerous regulation,” a company co-founder, LeGrand Crewse, said in an interview, noting that helmet requirements were also modest, depending on the state and the rider’s age.

Law enforcement officials have begun to express concerns about the minimal training required of teenage e-bike owners, and about their behavior. Car drivers ages 16 to 19 are three times as likely to be killed in a crash as drivers 20 or older, and bicyclists ages 10 to 24 have the highest rate of emergency room visits for crashes, according to the Centers for Disease Control and Prevention. Some states have begun to raise the training requirements for young drivers, including adding graduated license programs that require extended hours of supervised driving, limit night driving or restrict the number or age of passengers.

The California Legislature is considering a bill that would prohibit e-bike use by people under 12 and “state the intent of the Legislature to create an e-bike license program with an online written test and a state-issued photo identification for those persons without a valid driver’s license.”

“I know the e-bike situation is evolving,” said Sergeant Collis of the San Diego County Sheriff’s Office. “But personally, with all these bikes, you should have at least a permit or a license to ride them at the speed they’re going.”

As a transportation solution, e-bikes seem promising. “I’m really bullish about middle and high schoolers being able to use e-bikes,” said Ms. Hultin of Bicycle Colorado. She noted that e-bikes offered children and busy families more transportation options at lower cost. But she worried that the vehicles could lead to an unsafe mix of untrained e-cyclists and unaware car drivers.

That problem, Ms. Hultin said, was exacerbated by “an algae bloom of noncompliant e-bikes.” She was referring to products on the market that call themselves e-bikes but are not, either because they can go faster than allowed by law or because, once purchased, they can be modified to do so.

One vehicle that has drawn attention for its speed is made by Sur-Ron, whose products have been involved in several recent deaths. In June in Cardiff, Wales, two boys on a Sur-ron bike died in a crash while being followed by the police; days earlier, a boy riding a Sur-ron in Greater Manchester had died after colliding with an ambulance.

In its marketing materials, Sur-ron describes one model, the Light Bee Electric Bike, as “easy to maneuver like a bicycle, with the torque and power of an off-road motorcycle.” Its operating manual cautions the owner to “please follow the traffic rules and with the safe speed (the top speed for this electric vehicle is 20 km/h).”

But the speed restraint — equivalent to about 12 m.p.h. — can be removed by simply clipping a wire, a procedure that is widely shared in online videos, and which law enforcement officials said appeared to be there by design.

“There are all kinds of videos on how to jailbreak your Sur-ron,” said Capt. Christopher McDonald of the Sheriff’s Department in Orange County, Calif., where e-bike accidents and injuries are rising. With the speed wire clipped, the vehicle can approach 70 miles per hour, he said. Several requests for comment were sent through the Sur-ron website but did not receive a response.

Matt Moore, the general counsel for PeopleForBikes, the main trade group for bicycles and e-bikes, said he worried about products like Sur-ron’s. “Some products are sold as ostensibly compliant but are easily modified by the user with the knowledge and presumably the blessing of the manufacturer,” he said. “Unfortunately, there appears to be a lack of resources at the federal level to investigate and address e-mobility products that may actually be motor vehicles.”

Tragedy in Encinitas

The day after Brodee entered the hospital, his family sat at his bedside. They played his favorite music, including Kendrick Lamar and early Wu-Tang Clan. “I read to him for hours,” his mother said. “We wanted to wake up his brain.”

Three days later, as Brodee clung to life, Niko Sougias, the owner of Charlie’s Electric Bike, a popular e-bike shop in town, was driving in Encinitas on Highway 101 when he saw two teenage boys riding Sur-Rons in the opposite direction.

“They were doing wheelies,” Mr. Sougias said. He has grown concerned about the e-bike industry, he said, and does not sell many models that are popular with teenagers.

His route that Saturday followed the path of the boys on the Sur-rons. Moments later, after a turn, Mr. Sougias saw that one of the Sur-Ron riders had collided with an S.U.V., had been thrown from his bike and was under a BMW.

According to the police, the Sur-ron rider had been seen driving recklessly and was found at fault. “He was lucky to escape with his life,” Mr. Sougias said.

Ms. Champlain was at the hospital with Brodee when the boy who had been riding the Sur-ron was brought in. Paramedics stopped by Brodee’s room to check in. “I can’t believe I’m here again for this,” she said one of them had told her; the same paramedic had brought in Brodee by ambulance.

Hours later, Brodee was pronounced dead. He was a beloved young man with a bright future ahead of him. He was fluent in Spanish and had a college-level knowledge of Japanese; he could dead-lift 300 pounds and, in 2020, was named student of the year at his high school. “I had so many people call me to tell me they’d lost their best friend,” his mother said.

Ms. Champlain said witnesses had told her that her son “did everything right,” including signaling to make a left turn.

“There should be more education for drivers with the change that’s happened,” she said. “I’d never seen an e-bike on the road until three years ago. Now I see hundreds.”

“They’re treated like bicycles when they’re not. They’re not equal.”