The streets of Washington, D.C., roared with the sound of thousands of motorcycles on Sunday during the 20th annual "Ride for Freedom," sponsored by the Rolling Thunder veterans group.
Over the years, the ride has grown steadily. Tens of thousands of bikers now come to the capital to make noise and draw attention to veterans' issues, including the plight of the missing in action.
The growth of the ride mirrors the growth of motorcycle ridership nationally. And as the number of motorcycles on the road rises, so does the number of motorcycle deaths.
A recent government report found motorcycle deaths have more than doubled in the past 10 years. Nearly 4,800 people died last year in motorcycle accidents and 87,000 were injured.
Mary Peters, the U.S. secretary of Transportation, is one of the six million Americans who rides motorcycles. She is campaigning to get every American who rides a bike to first put on a helmet.
"Of the motorcycle fatalities over the last year, 700 of them would likely not have died had they had a helmet on," said Peters. "I hope I'm setting the right kind of role model by wearing all my safety equipment, that I check out my bike before I leave, that I ride with others so that we are more visible."
But the government says 14 percent of motorcycle helmets will not actually protect a rider in a crash. Marketed as "novelty" helmets, they look like the real thing, but offer little protection. Peters encourages every rider to use only a helmet certified by the Department of Transportation.
A research lab in Los Angeles tested certified and uncertified helmets. It found a certified helmet will prevent concussion in a fall from six feet. Uncertified helmets were not effective in a fall of just three feet.
"When you put [the novelty helmet] on your head, it will protect you from the rain, but don't fall on it because there is nothing there that will absorb any impact," said Harry Hurt of the Head Protection Research Laboratory.
So why do so many riders opt for less safety?
"Some people just believe in flouting the system," said Harry Avila, a Harley Davidson rider. "They think they're cool."
Other people, Peters believes, just don't know any better. Those are the riders she is hoping to reach.
ABC's Lisa Stark contributed to this report.