An all-terrain vehicle (ATV), also known as a three wheeler, four wheeler, quad bike, or quad, is defined by the American National Standards Institute (ANSI) as a vehicle that travels on low pressure tires, with a seat that is straddled by the operator, along with handlebars for steering control. As the name implies, it is designed to handle a wider variety of terrain than most other vehicles. Although it is a street-legal vehicle in some countries, it is not street legal within most states and provinces of Australia, the United States and Canada. By the current ANSI definition, it is intended for use by a single operator, although some companies have developed ATVs intended for use by the operator and one passenger. These ATVs are referred to in this notice as tandem ATVs.
The rider sits on and operates these vehicles like a motorcycle, but the extra wheels give more stability at slower speeds. Although typically equipped with three or four wheels, six-wheel models exist for specialized applications. Engine sizes of ATVs currently for sale in the United States, (as of 2008 products), range from 49 to 1,000 cc (3 to 61 cu in).
Honda made the first three-wheeled ATVs in 1970, which were famously portrayed in the James Bond movie, Diamonds Are Forever and other TV shows such as Magnum PI and Hart to Hart. Dubbed the US90 and later—when Honda acquired the trademark on the term—the ATC90 (All Terrain Cycle), it was designed purely for recreational use. Clearly influenced by earlier ATVs, it featured large balloon tires instead of a mechanical suspension.
By the early 1980s, suspension and lower-profile tires were introduced. The 1982 Honda ATC200E Big Red was a landmark model. It featured both suspension and racks, making it the first utility three-wheeled ATV. The ability to go anywhere on terrain that most other vehicles could not cross soon made them popular with US and Canadian hunters, and those just looking for a good trail ride. Soon other manufacturers introduced their own models.
Sport models were also developed by Honda, which had a virtual monopoly in the market due to effective patents on design and engine placement. The 1981 ATC250R was the first high-performance three-wheeler, featuring full suspension, a 248 cc two-stroke motor, a five-speed transmission with manual clutch, and a front disc brake. For the sporting trail rider, the 1983 ATC200X was another landmark machine. It used an easy-to-handle 192 cc four-stroke that was ideal for new participants in the sport.
Over the next few years, all manufacturers, except Suzuki, developed high performance two-stroke machines, but did not sell as many due to the reputation already secured by Honda. These models were the Yamaha Tri-Z YTZ250 with a 246 cc two-stroke engine and a manual 5- or 6-speed gearbox and the Kawasaki Tecate KXT250 with a 249 cc two-stroke with a 5-speed gearbox. Other smaller or lesser known companies, such as Tiger ATV, Franks, and Cagiva, produced racing three wheelers, but in much smaller numbers. Few of these machines are known to exist today and are highly sought by collectors. There is a fan base for three wheelers 
Production of three wheelers ceased in 1987 due to safety concerns: Three wheelers were more unstable than Four wheelers (although accidents are equally severe in both classes). A ban on sales of new or used three wheelers and a recall of all remaining three wheelers has been proposed by the American Academy of Pediatrics.
Suzuki was a leader in the development of 4-wheeled ATVs. It sold the first ATV, the 1982 QuadRunner LT125, which was a recreational machine for beginners.
In 1985 Suzuki introduced to the industry the first high-performance 4-wheel ATV, the Suzuki LT250R QuadRacer. This machine was in production for the 1985-1992 model years. During its production run it underwent three major engineering makeovers. However, the core features were retained. These were: a sophisticated long-travel suspension, a liquid-cooled two-stroke motor and a fully manual 5-speed transmission for 85–86 models and a 6-speed transmission for the 87–92 models. It was a machine exclusively designed for racing by highly skilled riders.
Honda responded a year later with the FourTrax TRX250R—a machine that has not been replicated until recently. It still today win all sorts of trophies and is a competiter even to big bore ATVs. Kawasaki Heavy Industries responded with its Tecate-4 250.
In 1987, Yamaha Motor Company introduced a different type of high-performance machine, the Banshee 350, which featured a twin-cylinder liquid-cooled two-stroke motor from the RD350LC street motorcycle. Heavier and more difficult to ride in the dirt than the 250s, the Banshee became a popular machine with sand dune riders thanks to its unique power delivery. The Banshee remains popular, but 2006 is the last year it was available in the U.S. (due to EPA emissions regulations); it is still available in Canada, however.
Shortly after the introduction of the Banshee in 1987, Suzuki released the LT500R QuadRacer. This unique quad was powered by a 500 cc liquid cooled two stroke engine with a 5-speed transmission. This ATV earned the nickname "Quadzilla" with its remarkable amount of speed and size. While there are claims of 100+ mph stock Quadzillas, it was officially recorded by 3&4 Wheel Action magazine as reaching a top speed of over 79 mph (127 km/h) in a high speed shootout in its 1988 June issue, making it the fastest production ATV ever produced. Suzuki discontinued the production of the LT500R in 1990 after just 4 years.
At the same time, development of utility ATVs was rapidly escalating. The 1986 Honda FourTrax TRX350 4x4 ushered in the era of four-wheel drive ATVs. Other manufacturers quickly followed suit, and 4x4s have remained the most popular type of ATV ever since. These machines are popular with hunters, farmers, ranchers and workers at construction sites.
Safety issues with 3-wheel ATVs caused all manufacturers to switch to 4-wheeled models in the late '80s, and 3-wheel models ended production in 1987, due to consent decrees between the major manufacturers and the Consumer Product Safety Commission—the result of legal battles over safety issues among consumer groups, the manufacturers and CPSC. The lighter weight of the 3-wheel models made them popular with some expert riders. Cornering is more challenging than with a 4-wheeled machine because leaning into the turn is even more important. Operators may roll over if caution isn't used. The front end of 3-wheelers obviously has a single wheel, making it lighter, and flipping backwards is a potential hazard, especially when climbing hills. Rollovers may also occur when traveling down a steep incline. The consent decrees expired in 1997, allowing manufacturers to, once again, make and market 3-wheel models, though there are none marketed today. Recently the CPSC has succeeded in finally banning three wheeled ATV's with attachments to bill HR4040. Many believe this is in response to Chinese manufacturers trying to import three wheeled ATV's. The Japanese manufacturers were also behind this legislation as they have been held responsible for years to provide ATV Safety training and to apply special labels and safety equipment to their ATVs while Chinese manufacturers did not.
Models continue, today, to be divided into the sport and utility markets. Sport models are generally small, light, two-wheel drive vehicles that accelerate quickly, have a manual transmission and run at speeds up to approximately 80 miles per hour (128.75 km/h). Utility models are generally bigger four-wheel drive vehicles with a maximum speed of up to approximately 72.5 miles per hour (116.37 km/h). They have the ability to haul small loads on attached racks or small dump beds. They may also tow small trailers. Due to the different weights, each has advantages on different types of terrain.
Six-wheel models often have a small dump bed, with an extra set of wheels at the back to increase the payload capacity. They can be either 4-wheel drive (back wheels driving only), or 6-wheel drive.
Sport models are built with performance, rather than utility, in mind. To be successful at fast trail riding, an ATV must have light weight, high power, good suspension and a low center of gravity. These machines can be modified for such racing disciplines as motocross, woods racing (also known as cross country), desert racing (also known as Hare Scrambles), hill climbing, ice racing, speedway, Tourist Trophy (TT), flat track, drag racing and others. Examples of high-performance models (racing) include the Yamaha YFZ450, Honda TRX450R, Suzuki QuadRacer R450, Kawasaki KFX450R, Can-Am DS450, Polaris Outlaw 525 S, Predator and the Outlaw 450 MXR, as well as the original sport models no longer produced, such as the Honda TRX250R, Suzuki LT250R and LT500R Quadracers. And also the two strokes like the Yamaha Blaster and the Yamaha Banshee
ATVs designed for fast trail riding include the Yamaha Raptor 700R/660R, Yamaha Raptor 350, Kawasaki Mojave 250, Kawasaki Lakota Sport 300, Honda Sportrax 400EX, Suzuki QuadSport Z400, Kawasaki KFX400, Bombardier/Can-Am DS650, Can-Am DS-450, Arctic Cat DVX400, Polaris Scrambler 500, Polaris Outlaw 500, Polaris Outlaw 525 (independent rear suspension IRS), Kawasaki KFX700, Polaris Predator 500, Can-Am Renagade 800, ADLY 320U Commander, 320S Taifun, New Force 500S/500L Hunter, Gamax AX 300 Tenet and AX500 EFI Emperor. Three-wheeled performance models included the Honda ATC250R (1981–1986), Yamaha YTZ250 Tri-Z (1985–1986), Kawasaki KXT250 Tecate (1984–1987) and the Tiger 250 and 500 (mid 1980's).
Three-wheelers designed for fast trail riding include the Honda ATC350X and the Honda ATC200X. Dakar Rally Moto Group 3 quads are designed for toughness and adaptability to a very wide range of dry terrain.
ATVs were first introduced in the early 1970s and almost immediately realized alarming injury rates for children and adolescents. According to medical literature, ATVs are as dangerous as Motorcycles, based on mortality and injury scores. More children and women are injured on ATVs, who also present a lower rate of helmet usage.
In the United States, statistics released by CPSC (Consumer Product Safety Commission) show that in 2005, there were an estimated 136,700 injuries associated with ATVs treated in US hospital emergency rooms. In 2004, the latest year for which estimates are available, 767 people died in ATV-associated incidents. According to statistics released by CPSC, the risk of injury in 2005 was 171.5 injuries per 10,000 four-wheel ATVs in use. The risk of death in 2004 was 1.1 deaths per 10,000 four-wheelers in use. Focus has shifted to machine size balanced with the usage of ATVs categorized by age ranges and engine displacements—in line with the consent decrees. ATVs are mandated to bear a label from the manufacturer stating that the use of machines greater than 90 cc by riders under the age of 12 is prohibited. This is a 'manufacturer/CPSC recommendation' and not necessarily state law.
The American Academy of Pediatrics and the CPSC recommended that no children under the age of 16 should ride ATVs. A Canadian study stated that "associated injury patterns, severity, and costs to the healthcare system" of pediatric injuries associated to ATVs resemble those caused by Motor Vehicles, and that public policies should reflect this fact
In 1988, the All-terrain Vehicle Safety Institute (ASI) was formed to provide training and education for ATV riders. The cost of attending the training is minimal and is free for purchasers of new machines that fall within the correct age/size guidelines. Successful completion of a safety training class is, in many states, a minimum requirement for minor-age children to be granted permission to ride on state land. Some states have had to implement their own safety training programs, as the ASI program cannot include those riders with ATVs outside of the age/size guidelines, which may still fall within the states laws.
According to The New York Times on September 2, 2007, the Consumer Product Safety Commission met in March 2005 to discuss the dangers of ATVs. Data from 2004 showed 44,000 children under 16 injured while riding ATVs, 150 of them fatally. Says the Times, "National associations of pediatricians, consumer advocates and emergency room doctors were urging the commission to ban sales of adult-size ATVs for use by children under 16 because the machines were too big and fast for young drivers to control. But when it came time to consider such a step, a staff member whose name did not appear on the meeting agenda unexpectedly weighed in." That staff member was John Gibson Mullan, "the agency’s director of compliance and a former lawyer for the A.T.V. industry" - the Times bases the claim on a recording of the meeting. Mullan reportedly said that the existing system of warnings and voluntary compliance was working. The agency's hazard statistician, Robin Ingle, was not allowed to present a rebuttal. She told the Times in an interview, "He had hijacked the presentation. He was distorting the numbers in order to benefit industry and defeat the petition. It was almost like he still worked for them, not us." CPSC reports of ATV deaths and injuries show an increase in the raw numbers of deaths and injuries that is statistically significant. The rate of deaths and injuries, which takes into account the fact that the number of ATVs in use has risen over the last ten years, has been shown to have experienced no statistically significant change.
The United States government maintains a website about the safety of ATVs where safety tips are provided, such as not driving ATVs with a passenger (passengers make difficult or impossible for the driver to shift their weight, as required to drive an ATV) or not driving ATVs on paved roads (ATVs usually have a solid rear axle with no differential). There also exists a website created by parents whose children died in ATVs accidents.
ATVs accounted for 58% of the SI (spark ignited) recreational vehicles in the US in the year 2000. That year, recreational SI vehicles produced 0.16% of NOx, 8% of HC, 5% of CO and .8% of PM emissions for all vehicles, both highway and nonroad. As a point of comparison, the nonroad SI < 19 kW (~25 hp) category (small spark ignition engines such as lawnmowers) comprised 20% of HC and 23% of CO total emissions. While recreational SI vehicles produce an aggregate of <4% of all HC emissions in the US, based on the relatively small population of ATVs (<1.2M) and small annual usage (<350 hrs), EPA emission regulations now include such engines, starting with the model year 2006. Engines meeting these standards now produce only 3% of the HC emissions that previously unregulated engines did.
In some countries where fencing is not common, such as the US, Canada and Australia, a small percentage of ATV riders knowingly cross privately owned property in rural areas and travel over public/private properties, where their use is explicitly limited to trails. Subsequently, environmentalists criticize ATV riding as a sport for excessive use in areas biologists consider to be sensitive, especially wetlands and sand dunes and in much of inland Australia.
While the deep treads on some ATV tires are effective for navigating rocky, muddy and root covered terrain, these treads are also capable of digging channels that may drain bogs, increase sedimentation in streams at crossings and damage groomed snowmobile trails. Proper trail construction techniques can mitigate these effects. Studies have also shown that ATVs may help in the spread of invasive species such as Centaurea and Lantana. Because both scientific studies and U.S. National Forest Service personnel have identified unregulated Off-Road Vehicles (ORVs) as the source of major detrimental impacts on national forests, the U.S. Forest Service is currently engaged in the Travel Management Process, wherein individual forests are restricting all off-road motorized travel to approved trails and roads. This is in contrast to its previously allowed, unregulated cross-country travel across all national forest lands, except for specifically designated wilderness areas. Although ORVs had been identified 30 years ago as a threat to wild ecosystems by the Forest Service, only after pressure by an unlikely alliance of environmentalists, private landowners, hunters, ranchers, fishermen, quiet recreationists and forest rangers themselves (who identified ORVs as a "significant law enforcement problem" in national forests ) has action been taken. The Travel Management Rule  was initiated in 2004; completion is expected in 2010.
Throughout the United States and the United Kingdom there are many quad racing clubs with enduro and quadcross sections. GNCC Racing began around 1980 and includes hare scramble and enduro type races. To date, events are mainly held in the eastern part of the United States. GNCC racing features many types of obstacles such as, hill climbing, creek and log crossings, dirt roads and wooded trails.
ATV National Motocross Championship was formed around 1985. ATVMX events are hosted at premiere motocross racetracks throughout the United States. ATVMX consists of several groups, including the Pro (AMA Pro) and Amateur (ATVA) series. Friday involves amateur practicing and racing on Saturday and Sunday. Saturday also involves racing for the Pro Am Women and Pro Am Unlimited classes. Sunday involves racing for the Pro and Pro Am production ATVs, but are scored separately. On average weekend over 500 racers will compete.
Championship Mud Racing/CMR saw its infancy in 2006 as leaders of the ATV industry recognized a need for uniformity of classes and rules of various local mud bog events. Providing standardized rules created the need for a governing body that both racers and event promoters could turn to and CMR was born. Once unified, a true points series was established and lead to a national championship for what was once nothing more than a hobby for most. In 2007 the finalized board of directors was established and the first races were held in 2008. Currently, the CMR schedule includes eight competition dates spanning from March to November. Points are awarded throughout the season in several different competition classes of ATV and SxS Mud Racing. The 2008 year included Mud Bog and Mudda-Cross competitions, but the 2009 and future seasons will only have Mudda-Cross competitions. Classes range from 0–499 cc to a Super-Modified class which will allow any size ATV in competition. The ultimate goal of The CMR is “to see the growth of ATV Mud Racing as a competitive sport and give competitors a pedestal upon which they can receive the recognition from national media and industry sponsors that they have long deserved.”