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Bicyclist Bob Krzewinski remembers the hit-and-run vividly: On a Sunday morning in 2006, a driver slammed into him from behind on a residential street, just a block from his home in Ypsilanti, Michigan. The force of the blow sent him tumbling and knocked off his glasses.

The driver of the white car slowed down briefly before peeling off — leaving the dazed Krzewinski lying on the ground with a badly injured left arm.

Related: Five Bicyclists Killed in Horrific Hit-and-Run ID'd

"I like to tell people that I saw the very worst in human behavior before I saw the very best," the 62-year-old former airline pilot told NBC News on Friday, referring to bystanders who rushed to his aid. "That driver basically left me for dead."

Krzewinski missed work for five months while undergoing physical therapy. But he was lucky that he didn't become one of the growing number of adult American men dying in bicycle crashes involving motor vehicles — despite a major decline in the overall number of cycling deaths.

Bicycle safety is again in the spotlight after five people were killed and four others were injured Tuesday near Kalamazoo, Michigan, after being hit by a driver who had reportedly been driving erratically. Two of the five who died were men, and all were older than 50.

An analysis of bicycle deaths by the Insurance Institute for Highway Safety, based on U.S. Department of Transportation data, found that 551 adult male bicycle riders died in crashes involving a motor vehicle in 2014. That's the highest number of fatalities for the category since at least 1975.

Sixty-eight adult women riders also were killed in vehicular crashes, the data shows. That number also has been trending up in recent years, though not as sharply as for male riders.

Meanwhile, the deaths of male and female riders younger than age 20 in motor vehicle crashes have fallen dramatically over the decades. In 2014, 81 young males and 13 young females were killed, according to the analysis.

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Overall in 2014, 720 bicyclists were killed in crashes with motorists, a 4 percent decline from 2013 and a 28 percent decline from 1975.

So why are older male riders seemingly more susceptible to those accidents?

Krzewinski speculates that older riders like himself are avid cyclists who go out more regularly and in organized packs.

But there's no easy answer for why one group is being killed at higher rates than others, transportation experts say.

"How much (a particular group) bikes might be a factor. Or how often they wear a helmet. But the data isn't there to accurately say," said James Gallagher, of the Pedestrian and Bicycle Information Center, which is part of the University of North Carolina's Highway Safety Research Center.

Gallagher said analyzing bike accidents is difficult because some states don’t compile information from reported crashes with the same diligence that they apply to motor vehicle accidents. Also, crashes involving a single rider or occurring off road often are not reported to police, he said.

Even so, the accident near Kalamazoo appears to be an anomaly.

"That was a very, very strange thing to happen," Gallagher said. "I can't recall anything of that magnitude."

The 50-year-old driver of the car, Charles Pickett Jr., who police say had initially fled the scene, has been charged with five counts of second-degree murder and four counts of reckless driving causing serious impairment. Police have not given a reason for why he allegedly slammed into the bicyclists.

With the rise in commuter riding and bike-sharing programs, some cities have recently sought to improve bicycle safety through safer riding initiatives and by creating bike lanes that separate cyclists from motor vehicle traffic.

In Philadelphia, which has the highest percentage of residents biking to work of any major U.S. city, advocates are calling for more red-light cameras to deter speeding drivers as well as protected bike lanes, reported NBC Philadelphia.

Gallagher noted that some states also are enacting "safe passing" laws that require drivers to keep a certain distance — typically 3 feet — away from riders or get ticketed.

Bicyclists commute during the morning rush hour past cars in Seattle. Elaine Thompson / AP, file

Thirty-six states and Washington, D.C., have such laws, according to the League of American Bicyclists.

The state of Michigan does not have a "safe passing" law, but on Thursday, a Senate bill was introduced that would classify pedestrians, wheelchair-bound people and bicyclists as a "vulnerable roadway user." Drivers who injure such people would be subject to a year in jail or a $1,000 fine.

Krzewinski said such laws can be helpful, but safety comes down to a simple requirement: minding the rules of the road. He hopes to get that message across on Wednesday during a "Ride of Silence" around Ann Arbor in honor of those recently killed this week in his state.

"Yesterday I was at a trail crossing, the pedestrian light came on and a car shot through the intersection and didn't even stop to make a right turn," said Krzewinski, describing his latest brush with danger.

But drivers of motorized vehicles don't bear all the responsibility, he added.

"Cyclists have to pay attention to what they're doing and motorists need to understand they can take out someone in seconds," he said. "It's up to us to avoid these traumatic incidents."