On a recent summer day, Michael Smithers was cruising on his Yamaha Raptor four-wheeler down Crane Crossing Road near his Plaistow, N.H., home -- one of thousands of American teens doing exactly the same thing that afternoon. But his ride turned tragic.

Officials say a Newton police officer on routine detail motioned the 13-year-old to come over, but that he sped away. Navigating a corner, he was thrown from the vehicle and hit a tree. He died a short time later at Lawrence General Hospital.

His death -- the fifth such fatality among young people from Southern New Hampshire and the Merrimack Valley in the last three years alone -- highlights some of the problems in the complicated world of off-road recreation, especially where children are involved.

The boy was riding an all-terrain vehicle too large for him, based on manufacturers' recommendations; he was riding on a prohibited public road; and he was riding alone, in violation of a new state law.

But Michael was also an experienced driver, and many officials say age is not necessarily the best gauge of how large a vehicle a rider can handle. In addition, he had taken a safety course through the state Fish and Game Department, had been riding alone legally before a July law change and "loved (his) four-wheeler," as a note at his memorial site says.

Many ATV advocates, including local families whose children ride, say that while Michael's death was tragic, ATVs are not the killing machines some people make them out to be.

Some say problems arise when parents don't properly supervise their youngsters or buy machines too big for them.

The Consumer Product Safety Commission recommends that children 12 to 16 should ride ATVs that are between 70 and 90 cubic centimeters (cc) -- a measurement that correlates with engine size. Teens 16 years and older can ride machines over 90 cc.

Street motorcycles average about 500 cc, with Harley Davidsons having an engine size of 1,000 to 1,500 cc.

Michael was riding a bike that measured 660 cc, far above the recommended size guidelines, and he was alone. According to the new state law, children between the ages of 12 and 14 must ride with a licensed adult above the age of 18 -- even if they have taken the safety course. When children turn 14, they can ride unaccompanied only if they've taken the course.

Prior to July 1, Michael would have been allowed to ride by himself because he had taken the safety course. The old law stated that children between the ages of 12 and 14 could ride alone if they had taken the course.

In Massachusetts, children 12 or 13 can drive ATVs if directly supervised by an adult; those 10 or 11 must be supervised by an adult on the land where the operator lives; and those under 14 may also drive in sanctioned races or rallies. Those under 10 are prohibited from driving at all.

Most area ATV dealerships keep an eye on who's buying what machine, and if the size is appropriate.

Bill Atchison a sales manager at Plaistow Power Sports, said each employee must sign a form that states they won't sell people machines that do not comply with the Consumer Product Safety Commission's recommended age/size guidelines.

However, there are ways to circumvent the system. Atchison said. Sometimes the parents don't say the machine is really for their child. Many times, he added, people will buy ATVs through the classified ads in newspapers or through friends.

"They do send mystery shoppers in here," Atchison said of the Consumer Product Safety Commission. He said repeated violations can result in the dealer's inability to sell certain merchandise.

He said sales associates will recommend safety classes and at times get riders in touch with area clubs that may offer additional training. "It only takes one incident like that to give us a bad name," Atchison said, referring to Michael's accident. "He was a great rider, he'll be missed." But some riders say age/size recommendations shouldn't be one-size-fits-all. Bigger teens, they say, can't handle four-wheelers that are too small. In fact, they may damage the machines or themselves.

"You may have a 13-year-old that's 6-foot-2 and if you put them on a 90 cc machine they'll look like a gorilla on a tricycle," said Maj. Tim Acerno of the N.H. Fish and Game Department, which regulates ATV use. "They problem is when you put a child that is too small on too big of a machine. To drive one, you physically shift your weight one way or another. I'm hesitant though to do a size/age restriction legislatively. ... You know your child better than we do.

"They're extremely fun machines, but if used improperly they can be extremely dangerous."

Acerno compares operating an ATV with driving a car -- you have to know what you're doing before you head out on the road. He recommends all riders -- not just youngsters -- take a rider education course in addition to the rider safety course offered by Fish and Game.

It's something that could save your life, Acerno stressed. He said last year there were 25,000 ATVs registered with the state with an estimated 50,000 machines unregistered because they're only used for farm work and not used off of private property.

Last year there were between 60 and 70 reported crashes -- one of which killed a 43-year-old man in Campton.

In New Hampshire, 18 people have been killed in off-road crashes since 1991, including two local teenagers and a 9-year-old Hampstead, boy in the past two years alone. They include: Michael McKinnon, 14, of Salem, who struck a 20-foot long metal chain hanging across Arlington Pond in Salem on Dec. 29, 2000. Billy Doucette, 15, of Windham, who collided with a tree in a wooded area in Pelham on Nov. 23, 2001.

Geoffrey "Geoff" S. Yannalfo, 9, of East Hampstead, who was killed after a dirt bike struck him off Depot Road in Hampstead on Oct. 1, 2000. In Massachusetts, Jeffrey R. York, 16, of Groveland was killed after he struck a tree near his home while riding on an all-terrain vehicle. But those who ride off-road vehicles say riding has become a family activity with many mothers, fathers and children hitting the trails each week for a leisurely ride.

The Oliverios of Londonderry, N.H., are among them. Just about every Sunday the family hits the trails. Chris Oliverio and his wife, Tracey, say riding is a good way to spend time with their four sons. "My personal feeling is that anyone under 16 should be with an adult. My children always ride with me and they've taken the safety course," Chris Oliverio said, pointing out that his two oldest children could technically ride alone. "If you're 16 you can drive a car, so you can drive an ATV by yourself."

Oliverio often leads his family on trail rides, with his boys following behind. Tracey Oliverio takes the last position. He said he's not one of those parents who use ATVs as a "mechanical baby sitter."

His twin 14-year-old sons and his 12-year-old son do ride machines that are bigger than the Consumer Product Safety Council recommends. But, he adds, they've been riding for at least four years and are too big -- and experienced -- for the recommended ATVs. However, the biggest machine they'll ride is 250 cc.

Tracey Oliverio admits that she "fought" her husband when he told her he'd like the boys to learn how to ride ATVs. Her husband has been riding for more than 20 years.

"I fought him for awhile and then I went out riding," she said, adding that she now loves the sport. "But I am still a stickler for the rules. ... We like to know where (the kids) are and keep a visual on them. We don't let them take off."

As Justin and Corey Oliverio, 14, adjusted their gloves and tinkered with their ATVs at one of the entrances to the Rockingham Trail in Derry last week, they talked about riding. Justin said he knows not to go out alone, even when his friends ask him to ride.

"Some (of my friends) tell me how they were doing doughnuts and spinning around and I try to tell them that's not what they're supposed to do," Justin said. "I tell them they should be riding with an adult." Joe Norton of Salem, N.H., who accompanied the Oliverios on their ride last week, said his 14-year-old daughter Amanda also knows not to ride alone. He said either he or his wife, Lori, accompanies her. "She took a safety course through her school -- Fish and Game came down," Norton said. "When she was 12, I made her take the course first and then we bought the machines. I bought her the biggest she was allowed on and we have a lot of fun with it."

Riders say that it's not difficult to operate an ATV, but that there are some things new riders should learn before they take to the trails themselves, such as how to turn and go up and down hills. The Oliverios say besides basic riding skills, all riders should be familiar with landowners' rights and what to do if you're on the trail and encounter an animal, such as a horse.

"Accidents do happen, even with adults around," Norton said. "But most of the time they happen when kids are unsupervised." Acerno said he understands that parents are put in a tough position when their teens want to head off on their ATVs alone. But they need to be aware of state laws and of their child's maturity level, both physically and mentally, he said.

"We tell parents to take responsibility for their children, not just turn them loose," Acerno said. "Look at your average 12- or 13-year-old. Should they be out by themselves?"

He said parent responsibility also comes into play when deciding how big of a machine to buy a teen. Acerno said as an instructor for the ATV Safety Institute, he has to turn away teens if they're on a machine that's too big for them as recommended by the Consumer Product Safety Commission. He said while he understands the recommendations, he thinks the guidelines need to be revisited.