Young Riders Not Big or Heavy Enough to Ride ATVS

The disproportionate percentage of injuries and deaths suffered by young riders on adult All-Terrain Vehicles (ATVs) illustrates the risks of this mismatch, but a group of Illinois emergency medicine doctors and medical researchers have conducted a study pinpointing one of the causes: young riders don’t have the physique to control adult-sized ATVs.

Researchers from the University of Illinois, College of Medicine, Saint Francis Medical Center, Bradley University; and the Neurological Institute sought to measure how the physical characteristics of riders, including height, weight and fingertip-to-fingertip length (wingspan), influenced their ability to safely control the ATV and avoid ejection. The researchers instrumented two ATVs, a Polaris Trailblazer 250 (a sport model), and a Honda FourTrax 250 (a utility model), to measure a rider’s body position in three maneuvers associated with crashes: the J-hook, the brake test, and the bump. Researchers were studying the lateral, longitudinal, and vertical dynamics in five riders of varying heights, weights, and wingspans, who had average experiences driving passenger vehicles, but no experience riding ATVs.

The study, published in the November issue of Neurosurg Focus, concluded:

“Individuals with light weights and small wingspans, such as those in the pediatric population, are under considerable risk of injury when operating an ATV due to lateral, longitudinal, and vertical operational instability.”

The researchers cited the grim toll ATVs have taken over a five year period, from 1997 to 2001, with injuries outpacing the increase in ATV use by a considerable margin. According to the US Consumer Product Safety Commission study, the number of ATV riders increased from 12 to 16.3 million (36 percent); the total number of riding hours went from 1.575 to 2.364 billion (50 percent), and the number of ATVs in use rose from 4 to 5.6 million (40 percent). Injuries, as measured by emergency room visits, however, shot up from 52,800 to 110,100 – a 109 percent increase.

These injuries occur disproportionately in riders less than 16 years of age. The study’s authors point out that children in this age-set make up only 17 percent of all ATV riders, but account for 31 percent of injuries and 26 percent of fatalities in 2001. Injured children have a high incidence of central nervous system trauma. Moreover, 85 percent of child riders rode adult-sized ATVs, and 87 percent of those injured were riding on an adult-sized ATV. In a two-year CPSC analysis of 1999-2000, 93 percent of fatalities occurred on adult-sized machines. Rollovers were associated with 40 percent of the fatalities; ejection accounted for 15 percent.

In recognition of these hazards, injury prevention advocates in Massachusetts succeeded in persuading lawmakers that children cannot safely ride ATVs. In July 2010, the state became the first in the nation to ban children under age 14 from riding ATVs, unless it is under the auspices of an organized race or event supervised by an individual 18 years or older. Teens between the ages of 14 and 16 are limited to riding ATVs or other recreational utility vehicles with an engine capacity of 90 cubic centimeters or less. ATV owners are required to register their vehicles. Although the new law will soon celebrate its first anniversary, the state has done little to enforce it, and has failed to publicize it.

Since 2009, the importation and sales of three-wheeled ATVs was banned and manufacturers have been required by the U.S. Consumer Product Safety Commission to file and implement voluntary action plans. These plans include commitments to provide safety information and guidelines regarding the appropriate age for child and adult-sized machines. The manufacturers also consented to instruct dealers not to market adult machines to child riders and conduct under-cover monitoring to ensure that dealers are complying.

In the Illinois field study, the researchers tracked the center of gravity of the ATV and the rider, allowing them to determine the weight distribution, lateral, longitudinal, and vertical displacements, and a rollover risk estimate. The J-Hook test was an adaptation of the National Highway Traffic Safety Administration designed to assess a vehicle’s lateral stability and rollover propensity. Researchers instructed riders turning to the left to suddenly veer right to gauge lateral movement under centrifugal forces – a common injury scenario involving young riders who roll the ATV while traversing level ground.

The brake test measured the longitudinal displacement of a rider in a sudden deceleration. The rider accelerated from a stop along a linear path at a certain minimum speed, and then braking suddenly at a pre-set location. This test allowed researchers to measure the longitudinal displacement of the rider while braking.

The bump test measured a rider’s vertical bounce when driving over a 3.5 inch-high bump, based on “the premise that riders’ safety is severely compromised once they are in a position in which their legs are completely extended. Any displacement beyond this boundary could cause their feet to leave the foot pegs—a condition conducive to ATV/rider separation. Similarly to longitudinal displacement, without restraint, excessive vertical displacement from the ATV seat can easily lead to rider injury.”

The field tests determined that wingspan is associated with the ability to stabilize an ATV during the J-Hook test:  “Much of this effect is probably due to the need for the ATV rider to actively engage the vehicle to mitigate against rollovers. To maintain stability, a rider must coordinate the counterintuitive shifting of his or her body weight in the opposite direction of a turn. For these procedures, a large wingspan is certainly beneficial,” the study said.

The brake and bump test demonstrated that weight was associated with less risk of ejection – but it varied according to the design characteristics of the ATV. For example, the Honda utility ATV has a more stable design, sitting lower to the ground, with a firmer suspension. The Polaris sport ATV sits higher off the ground, with a bouncier suspension and a greater distance from its foot pegs to its seat, forcing the riders’ legs in a more extended in the sitting position. The result, “a rider will have less allowable bounce before their legs will reach full extension on the Polaris.” In the bounce test, “a weight of 75 lbs. marks the weight value at which a rider becomes unsafe on the Honda when riding over a 3.75-inch bump. On the Polaris, however, this weight value is 85 lbs.”

These findings align with the conclusions of CPSC mechanical engineers, who “have noted that a child who is too light or too heavy for the vehicle may affect the center of gravity and lead to instability.” But, this testing shows that weight is not the only determinant:

“As demonstrated by our testing, ATV rider stability and safety are also based on rider wingspan and weight, which may not be adequately addressed in the new top speed–related age requirements. Based on our findings, we recommend that ATVs designed for children should have both size and weight limitations for riders included as a stratification measure.”

“The implications of this study are enormous, especially for the pediatric population, because they have been found to be 4–12 times more likely to be injured riding an ATV than adult riders,” the study’s authors said.