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Photographer: Spencer Platt/Getty Images Photographer: Spencer Platt/Getty Images

The rate of cycling deaths among American children under the age of 15 has fallen 92 percent since 1975. That doesn't mean the roads are safer—it may just mean kids are riding bikes less.

The Centers for Disease Control reported today that the total rate of cycling deaths in the U.S. declined 44 percent from 1975 to 2012, a decline driven entirely by fewer deaths of kids. For adults, who are increasingly commuting on two wheels, the rates actually rose over the same period.

One big shift that may explain the decline: Kids are far less likely to ride their bikes to school than they were a generation ago. In 1969, 48 percent of American kids in kindergarten through 8th grade biked or walked to school. By 2009, that rate was just 13 percent, according to data in a 2011 article in the American Journal of Preventive Medicine.

"We’re not sure that the roads have become safer," says Jason Vargo, assistant scientist at the University of Wisconsin-Madison's Global Health Institute and the lead author of the report. "We may be just putting people out on the same roads that are as dangerous as they were before."

The percentage of kids who wear bike helmets has also increased, from 3.8 percent in 1991 to 12.1 percent in 2013, according to data from the Youth Risk Behavior Survey. Kids may also be spending less time riding around than they did in the 1970s, since video games and computers have entered the American household.

States varied widely, both in the rate of bike deaths and how that number has changed over the past four decades. Florida, Delaware, Louisiana, Arizona, and California had the greatest rates of cycling mortality. And while the death rate in most states has dropped substantially since the '70s, it barely budged in Florida:

The CDC analysis is drawn from a database of road deaths maintained by the National Highway Traffic Safety Administration that includes 29,711 cyclist deaths over 38 years. The records only count fatalities that involved a motor vehicle or occurred on public roads. Because they're expressed as mortality rates for the entire population, they don't account for changes in how many people ride bikes, how often they do it, or how far they travel.

Cyclists still die on the roads at twice the rate of vehicle occupants, though just 1 percent of all trips in the U.S. are made by bike. Vargo says he did the research to find out whether the increasing popularity of cycling—which many advocate as a public health intervention—is exposing people to greater risk of death.

He suggests that it doesn't have to be so, if cities and states promote cycling hand in hand with safety improvements, such as bike lanes, speed limits, speed bumps, helmet laws, and education for motorists and cyclists alike. Bike-friendly cities such as Portland, Ore., Austin, and Madison, Wis., have seen cycling rates increase without corresponding jumps in road deaths, Vargo says. "The local success stories really don’t suggest that more cycling leads to high fatality rates," he says. "The national numbers may hide that."