What Is an E-Bike, and How Safe Are They?

E-bikes are increasingly visible on roads and bicycle paths, with a growing number of teenagers among the riders. But the recent deaths of several teenage riders have raised concerns about the safety of some types of vehicles, and about whether they legally qualify as e-bikes. Here’s what’s known about e-bikes and their risks.

What Is an E-Bike?

The Consumer Product Safety Commission, the federal agency responsible for regulating the safety and sale of low-speed electric bicycles, defines an e-bike as a two- or three-wheel vehicle that has pedals and an electric motor.

The motor must be rated below 750 watts, which is roughly twice the power that a professional cyclist can generate. The rider can use the pedals or the motor, singly or in combination. With the motor alone, the bike must not be capable of going faster than 20 miles an hour on a level surface. State laws govern where e-bikes can be ridden, the minimum age for riders and other rules about how the vehicles are used.

To meet the federal regulations, bicycle manufacturers have developed a three-tier classification system for e-bikes.

Class 1: Maximum speed, 20 m.p.h.; the motor may provide power only while the rider is pedaling. (This is known as “pedal assist.”) Age restrictions: None in most states, although some states, such as Oregon, do not permit the use of any class of e-bike by riders younger than 16.

Class 2: Maximum speed, 20 m.p.h.; the motor may provide power independently of the pedals. Age restrictions: none in most states. (These e-bikes in particular attract criticism because, by relying solely on the motor, they can achieve immediate bursts of speed.)

Class 3: Maximum speed, 28 m.p.h. — but only if the pedals and the motor are used simultaneously. These vehicles are intended for commuters and other riders who are interested in traveling farther than a traditional bicycle would easily allow. Use not permitted by riders younger than 16, in many states.

Notably, the federal consumer agency does not recognize the three-class system.

What Are the State Rules?

According to PeopleForBikes, the trade group that helped craft the three-class system for manufacturers, 42 states have laws that are largely in line with the classification system. In most states, then, riders under 16 can use Class 1 and Class 2 e-bikes, while riders of Class 3 e-bikes must be 16 or older.

But enforcing those rules is tricky, according to local and state law enforcement officials. It can be hard to tell by looking if a teenage rider is too young for the e-bike being ridden. And glancing at an e-bike’s motor does not establish whether it can go faster than 20 m.p.h.

That has led some jurisdictions, such as Bend, Ore., to design public service campaigns alerting riders and parents to the laws. In Orange County, Calif., officials have impounded some models, like the Sur-ron, that the county considers to be unlicensed and unregistered electric motorcycles.

Why Is 20 M.P.H. Meaningful?

The origins of that parameter are unclear, safety experts said, but it appears to have emerged from legislative wrangling as a way to balance the risks posed by increased speed.

“That’s the point at which Congress, the Consumer Product Safety Commission and the Department of Transportation decided the break was between a consumer product and a motor vehicle,” said Chris Cherry, a professor of civil engineering at University of Tennessee who advises the federal government on e-bike safety.

By various measures, the risks of serious injury and death rise sharply at around 20 m.p.h., although much of that research involved collisions between cars and pedestrians. For instance, the risk of severe injury to a pedestrian is 25 percent when the car is moving at 16 m.p.h., and it rises to 50 percent at 23 m.p.h., according to the AAA Foundation for Traffic Safety. The risk of fatal injury follows a similar curve. But e-bikes are new, so there is much less data on the relationship between speed and injury risk.

Mr. Cherry said that the 28-m.p.h. limit appears to be derived from an effort to match the European standard of 45 kilometers per hour so that e-bike manufacturers could serve both markets.

But Don’t Many E-Bikes Go Faster Than 20 M.P.H.?

Yes.

E-bikes are allowed to go faster than 20 m.p.h., and up to 28 in the case of a Class 3 bike, if the rider is pedaling while also using the motor.

But those limitations can, in many cases, be bypassed with little effort. For instance, some e-bikes are sold with speed “governors” that restrict the speed at the point of sale to 20 m.p.h. But that electronic governor can be eliminated by cutting a wire or changing the limitation with a smartphone app. Unrestricted, some models can exceed 55 m.p.h. Law enforcement officials and industry experts have said that e-bike manufacturers who sell these products are aware that the speed governors are regularly removed.

“Some products are sold as ostensibly compliant but are easily modified by the user with the knowledge and presumably the blessing of the manufacturer,” said Matt Moore, the general counsel for PeopleForBikes, the trade organization that represents bicycle and e-bike manufacturers. “The real question is what to do about it.”

What Is Being Done About This Loophole?

Good question, safety experts say.

“PeopleForBikes has been pointing out these issues to regulators for some time now,” Mr. Moore 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.”

The federal government appears not to have a clear answer as to whether some of these products have ceased to be e-bikes — which are regulated by the Consumer Product Safety Commission, or C.P.S.C. — and instead have become motor vehicles, which are regulated by the National Highway Traffic Safety Administration.

A spokesperson for the federal consumer protection agency replied in an email that products that go at higher speeds “would be motor vehicles outside of C.P.S.C. jurisdiction” and added that the highway traffic agency “has jurisdiction over motor vehicles.”

The highway traffic agency responded to inquiries from The Times with a written statement: “Due to emerging e-bike designs that can vary in speed capability, in how they combine motor power and pedal power, and in other design factors, NHTSA is evaluating, in conjunction, with C.P.S.C., how best to oversee the safety of e-bikes.”