All-terrain vehicles are like large tricycles or minature carts with either three or four wheels usually 50 inches or less. The driver straddles the vehicle and steers with handle bars. A motorcycle engine drives the machine. Three wheelers are no longer manufactured because of high risk of roll overs, but many are still in use. Known as ATVs, these machines were created specifically for off-road travel. ATVs are generally equipped with wide, knobby or paddle-like tires and can carry one or two people at a time. There are approximately 2.4 million ATVs currently in use in the United States. ATVs are the fastest growing segment of the off road vehicle sector.
ATVs have a poor safety record, in part, because people drive them recklessly across the landscape. Almost 2800 deaths have been attributed to ATVs (about 200 to 300 annually) since 1985. The risk of death, approximately .8 to 1.0 per 10 000 ATVs, has remained fairly steady since 1987. Annual emergency department visits for treatment of ATV-related injuries reached a peak of 108 000 in 1986 and declined after that to the present level of about 54 500 annually.
Like dirt bikes, ATVs and the trails they create can be a major source of sedimentation. California researchers estimate that dirt bikes and ATVs produced as much as 72,000 metric tons of sediment in a single winter season.
Another study in the San Francisco Bay area found that two and four wheel vehicles increased surface strength and density, which caused increased runoff and decreased water infiltration, reduction of soil moisture and reductions in organic carbon. These impacts prevented revegetation, and the increased sediment yield and runoff were found to affect adjacent sites.
ATVs are also a major factor in the spread noxious and invasive weeds. Based on research by the Montana State University Extension Service, a single dirt bike or ATV can spread 2,000 seeds over a 10-mile radius.
Yet another area where ATVs (as well as other ORVs) affects natural system is disturbance to wildlife. In one study the effects of both pedestrian and ATV (four wheeler) effects on movement patterns of elk in the White River, Colorado, area. The mean distance moved by the elk in response to the ATV was more than twice the pedestrian mean. Longer flight responses, especially in fall, winter or spring when wildlife energy reserves are low can add considerably to the stress wildlife feel at these times of year.