Article Text
Abstract
Background All-terrain vehicle (ATV)-related deaths and injuries are a growing public health concern, particularly in rural and suburban communities. More engineering approaches that address vehicle safety and promote injury prevention are critically needed.
Objectives Our study was designed to determine the variability in seat characteristics among 2012 model-year, adult-size ATVs.
Methods Measurements of 67 models were performed using an image-based method. Seat characteristics were compared by manufacturer and by ATV type (sport vs utility).
Results There were significant differences in seat length and seat placement among manufacturers and between sport and utility ATVs. Seat lengths ranged from 19.8 to 37.0 inches, with sport models significantly longer than utility models. Longer seats resulted from the back of the seat extending further beyond the rear axle and/or the seat front extending closer to the handle grips. Seat front to handle grip distances ranged from 3.25 to 16.5 inches. Combined data showed a strong inverse correlation between seat length and the distance from the seat front to the handle grips, but no significant correlation with wheelbase or engine size.
Conclusions We found wide variability in seat length and placement for adult-size ATVs. However, existing seat specifications were identified that may be a good starting point for improved seat design. Optimal design would allow for safe operation while reducing the likelihood of multiple riders and use by underaged operators, both major risk factors for ATV-related deaths and injuries. Ultimately, regulations may be needed to ensure standardised seat design is incorporated throughout the ATV industry.
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Introduction
US all-terrain vehicle (ATV) crashes have resulted in over 800 deaths and more than 130 000 emergency department (ED) visits each year from 2004 to 2007, the last years for which Consumer Product Safety Commission data are considered complete.1 ,2 In 2008, over 400 000 non-fatal ATV-related injuries occurred; more than half of these injuries were treated outside the ED and many crash victims never sought medical care or were treated at other outpatient facilities.3 The total annual cost of deaths and injuries from ATV crashes have been estimated at over $22 billion, doubling from 1999 to 2007.3
A number of risk factors have been identified for ATV-related injuries. These factors include younger age, inexperience, being male, use of alcohol, riding on the road, lack of helmets, age-inappropriate vehicle size and carrying passengers.4–15 The likelihood and the severity of crashes have been shown to increase when multiple risk factors are involved.9 ,16 ,17 Moreover, available models have increased significantly in weight and maximum speed over the past 15 years. Some vehicles weigh over 700 pounds and many are capable of achieving highway speeds, even greater than 80 mph.6
A major contributor to paediatric deaths and injuries involves children riding as operators or as passengers on adult-size vehicles,3 ,6 ,18 both widely reported practices.3 ,19–23 Manufacturer's guidelines designate certain models as being appropriate for youth. Typically, these vehicles have engine displacement sizes of 90 cc or less. However, the Consumer Product Safety Commission found that in 2005, adult-size ATVs were associated with 94% of paediatric fatalities.3 The high speed and large size of adult-size ATVs create increased physical and mental demands, as well as anthropometric mismatches that increase the likelihood of crash and subsequent injury for children.
Another major risk factor is carrying passengers on single-person vehicles.24 Survey reports indicate that riding with passengers on ATVs is a common practice,6 ,19 ,21–23 and that many ATV users and non-users are unaware that having multiple riders on ATVs is unsafe.25 A study of 4684 Iowa school children revealed that of the 77% who had been on an ATV, 92% reported having ridden in the past with more than one rider.26 ATVs require ‘active riding,’ meaning that shifting of the rider's centre of mass is necessary to maintain vehicle stability, particularly when turning or riding on an incline.6 ,19 ,21 ,23 Passengers inherently decrease the ability of the operator to actively ride.
Engineering changes in vehicle design to increase safety have proven highly successful in reducing deaths and injuries for many types of motorised vehicles,28–30 but have not been a common strategy for ATVs. The proven value and limited use of engineering approaches for ATV injury prevention provided the rationale for our study. Specifically, design modifications to make it less likely that a child can drive an adult-size vehicle or eliminating seat features that allow for passengers are strategies that have not been explored. As a first step towards seat design modifications that might limit these unsafe driving practices, we measured seat length and placement for 2012 model-year, adult-size ATVs using a recently developed and validated image-based methodology.
Methods
ATV types
The vehicles included in these studies were single-person, adult-size, 4-wheeled ATVs, both sport and utility, from the 2012 model-year. Utility ATVs were defined as those with rear racks, and sport ATVs were those without (figure 1).3 ,6 Youth-size vehicles, that is, ATVs with engine sizes ≤90 cc and/or designated as a youth model by the manufacturer, were excluded from the study. This decision was based on the fact that there are unique issues surrounding youth-size ATVs and children, and the evaluation of their seat design merits separate discussion. Also not included in this study were side-by-sides, often referred to as utility vehicles (UTVs) or recreational off-highway vehicles. These vehicles are designed for multiple riders and equipped with roll bars and safety belts. Thus, seat design issues are significantly different between UTVs and ATVs.
Measurement methodology
Publically available ATV images were downloaded electronically and measurements were done using tools from Adobe Photoshop.31 A companion methods paper provides detailed steps for the image-based measurements performed, including validation techniques.31 The methodology was validated by comparing the image-based seat lengths, as determined by two independent measurers (20 models). The Pearson correlation coefficient for this comparison was 0.95, p<0.0001. Seat lengths using the image-based technique (12 models) were also compared with direct measurements of the same models at local dealerships. The Pearson correlation coefficient for this comparison was 0.96, p<0.0001.31 Only digital images for which the calculated vehicle length was <5% of the manufacturer's listed length were used for final analysis.
Vehicle measurements/distances
The image-based method was used to create a vertical plane connecting the centres of the front and rear axles.31 To set the grid scale in the plane, the wheelbase length, which is the distance from the front axle to the rear axle, was entered. Measuring tools were then used to determine distances between vertical lines in the plane that defined points on the vehicle. Lengths and distances in inches between these vertical lines were determined as shown below, where D1 was the distance from the front of the vehicle to the back of the seat, D2 was the distance from the front of the vehicle to the front of the seat and D3 was the distance from the front of the vehicle to the handlebars.
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Length of seat=D1−D2
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Distance from seat front to handle grips=D2−D3
In order to standardise the position of the back of the seat, we calculated it relative to the wheelbase using the formula below, where D4 was the distance from the centre of the front axle to the centre of the back of the seat.
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Position of the back of the seat (% of wheelbase) = D4/wheelbase × 100
Data analysis
Data analyses were done using Excel V.12.3.4 (Microsoft, Inc.) and Prism V.4.0c (GraphPad, Inc.). Comparisons of two medians were performed using the Mann–Whitney test, and of three or more medians using the Kruskal–Wallis test followed by the Dunn's post-test of multiple comparisons. Correlation analyses were performed for seat length versus seat front to handle grip distance, seat length versus wheelbase and seat length versus engine size. Correlation data are expressed as the Pearson coefficient (r). Significant differences for all analyses were defined as p<0.05.
Results
Seat length
Measurements of 67 adult-size ATV models from eight manufacturers were performed (table 1). Seat lengths ranged from 19.8 to 37.0 inches, the longest seat length being nearly twice that of the shortest. Sport ATV seats were significantly longer than those on utility ATVs (figure 2A).
An overall comparison by manufacturer showed that the median seat length was longest for Polaris and shortest for Arctic Cat (table 1). There was considerable variability in seat length by manufacturer for both utility and sport ATVs. For utility models, Polaris had significantly longer seats (median, 30.1 inches) than Yamaha (23.4 inches) and Arctic Cat (24.0 inches) (see figure 2B). Among sport models, the longest seats measured were Polaris ATVs (figure 2C). No usable Kymco sport model images were found. The relatively small number of sport models precluded further comparisons by manufacturer.
Front of the seat
The first measure of seat placement was the distance in inches from the seat front to the handle grips (table 2). Distances ranged from 3.25 to 16.5 inches, the longest distance being approximately five times farther from the handle grips than the shortest distance. Overall, Polaris had significantly shorter distances than Arctic Cat and Kymco.
The median distance for sport ATVs (6.17 inches) was significantly less than for UTVs (10.2 inches) (see figure 3A). In all, 18 of the 21 sport models measured had distances from the seat front to the handle grips of 7.97 inches or less, values that were less than half of the longest distance (16.5 inches) measured in the study. All but one sport model (distance 11.6 inches) had distances shorter than the median distance for utility ATVs.
Among utility models (figure 3B), seat fronts for Polaris (median, 5.6 inches) were significantly closer to the handle grips than those for Kymco (10.8 inches), Yamaha (11.3 inches) and Arctic Cat (12.1 inches). For sport ATVs (figure 3C), distances from the seat front to the handle grips also varied widely both by manufacturer and even among models of the same make (Can Am).
Back of the seat
The second measure of seat placement was the distance of the back of the seat from the front axle expressed as a percentage of the wheelbase length (table 3). The back of the seat on sport models extended further beyond the rear axle (median=112% of wheelbase) relative to those on utility ATVs (median=104% of wheelbase). There were no overall differences in this measure by manufacturer.
Figure 4A shows the distribution of the back of the seats for utility and sport ATVs. For utility models, 43 of 46 (93%) seat backs were located within 10% of the wheelbase length from the rear axle, with eight models (17%) at 90%–100% and 35 models (76%) at 101%–110%. In contrast, 18 of 21 (86%) sport models had seat backs located at more than 107% of the wheelbase length. The three sport models with seat backs closest to the rear axle were from Can Am.
Figure 4B,C shows graphical representations of seat placement for the three longest and three shortest seats from utility and sport models, respectively. ATV models with the shortest seats in relation to their wheelbase length were more likely to have the front of the seat start farther from the handle grips and the back of the seat end closer to the rear axle.
Correlations
Combined data showed a strong, highly significant inverse correlation between seat length and the distance from the seat front to the handle grips (figure 5A). There were no significant correlations between seat length and wheelbase length (figure 5B) or engine size (figure 5C).
When analysis was done by vehicle type, there were no significant correlations between seat length and wheelbase length for utility (figure 6A) or sport (figure 6B) models. Although a correlation was found between seat length and wheelbase for some manufacturers (data not shown), the correlation varied widely from strongly positive (Kawasaki, Suzuki) to moderately negative (Polaris, Arctic Cat).
Discussion
Active riding
ATVs have wide, knobby, low-pressure tires, a high centre of gravity, and a suspension system capable of handling rough terrain and cushioning jumps.6 Active riding requires the operators to shift their centre of gravity to maintain the stability of the vehicle, particularly while turning or when travelling on an incline.6 ,32–34
When going steeply downhill, operators must shift their weight back toward the rear axle with their arms extended. This maintains the operator's centre of gravity behind the front wheels and reduces the risk of a forward rollover. In contrast, operators lean their upper body forward toward the front wheels to keep proper centre of gravity when travelling uphill. On steeper uphill inclines, standing and leaning forward over the handle grips helps keep the centre of gravity in front of the back wheels and reduces the risk of rolling over backwards.35 An operator’s ability to use their weight to counteract changes in the vehicle's centre of gravity is critical for safe ATV operation and seat design must consider these dynamics.
Seat design and multiple riders
Risks associated with carrying passengers
Multiple riders increase the likelihood of a crash. A passenger represents a second centre of mass that must shift appropriately and sufficiently, in combination with the operator's mass, to prevent loss of vehicle control. Frequently, passengers are not able to see and react to changes in terrain and direction. This failure to anticipate operator and vehicle movements can contribute to rollovers, especially during turns and on side hills. Passengers seated behind an operator, and near or beyond the rear axle, increase the risk of a backward rollover on uphill inclines.36 On the other hand, passengers behind the operator could contribute to a forward rollover when going downhill, by preventing the operators from sufficiently shifting their weight back.
Passengers sitting in front of the operator may increase the likelihood of a backward rollover when going uphill by preventing the operator from moving/leaning sufficiently forward. In addition, passengers in front of the operator can interfere with vehicle steering. The presence of an ATV passenger also increases the likelihood of a victim falling off or being thrown from the vehicle during unexpected accelerations and sharp turns. Finally, regardless of seating position, extra riders can distract the operator from the complex decision-making processes required to handle unexpected features of the terrain.
Seat length
Most ATVs are designed for a single rider and the vehicles have safety warnings to this effect. Unfortunately, safety warnings have been shown to be of limited value for injury prevention,37 and studies show that more than half of injured ATV users either did not know whether their vehicle had warning labels or stated that it did not.6 Despite safety warnings, many ATV seats appear long enough to accommodate multiple riders. Youth in focus group studies felt that longer seats seemed to invite multiple riders and that riding with others facilitated socialising.4 These findings suggest that many ATV models may too easily accommodate more than one rider and may provide significant temptations to do so.
We found significant variability in seat length for utility and sport models both between and within major manufacturers. Moreover, there was no correlation between seat length and vehicle size, regardless of whether size was defined by wheelbase or by engine displacement (cc). There are no reported studies on seat length requirements for active riding. However, we would argue that if the shorter seat length of some available ATV models is sufficient for active riding and safe vehicle operation, then significantly longer seats serve no legitimate functional purpose.
Back of the seat location
ATV operators may need to shift their centre of gravity toward the rear of the vehicle on a steep downhill incline. However, the back of the seat does not need to surpass the extended grip of the typical operator. Moreover, longer seats could invite carrying passengers, which would prevent the operator from shifting backward. Passengers behind the operator also increase the risk of a backward rollover when travelling uphill and/or of passenger ejection to the rear of the ATV.
We found that almost all of the backs of utility ATV seats ended within 10% of the wheelbase length from the rear axle. In contrast, only three sport models, all from the same manufacturer, had the back of their seats end over or near the rear axle. Extension of the seat beyond the rear axle accounted in a large part for the significantly longer seats observed for sport versus utility ATVs. We speculate that the extension of sport ATV seats beyond the rear axle reflects the fact that sport models do not have a rear rack, whereas utility ATVs do, which limits seat extension beyond their rear axle. Importantly, our observation that some sport and most utility models have the back of their seats positioned at or near the rear axle suggests that this placement allows for safe operation of the vehicle, including sufficient shifting to the rear when driving downhill.
Seat design and youth riders/operators
Front of the seat location
Longer seats that start closer to the handle grips inappropriately allow for a rear passenger if the driver shifts forward, but could also encourage an adult operator to put a young child on a seat that extends in front of them. Although active riding does not require movement of the buttocks forward on the seat as previously discussed, passengers seated in front of the operator could interfere with shifting of an operator's torso forward on an uphill incline and with steering. Crashes also occur as a result of children in front of adults inadvertently accelerating the vehicle by grabbing the throttle.
Shorter distances from the seat front to the handle grips allow smaller children to sit close enough to the handle grips to operate the vehicle. Many adult-size ATVs in the study had distances short enough to allow younger children to steer the ATV, with the shortest distance being just over 3 inches. Conversely, ATVs with longer distances allow for adult operation, but make it very difficult for children to sit on the seat and reach the handle grips with sufficient bend in their arms to manoeuvre the vehicle. The longest distance from the seat front to the handle grips was 16.5 inches.
Although sport ATVs overall had shorter distances than utility ATVs, both types of vehicles had models with distances conducive to operation by youth. Because of the rear racks, much of the seat length variability noted among utility ATVs was due to seats starting closer to the handle grips. It is currently unclear why manufacturers extend seats for many models closer to the handle grips than is necessary for adult operation.
Limitations
Images of 2012 model-year vehicles were used and thus study results may not reflect the full variability and range in dimensions for all existing ATVs. Selection bias must also be considered when interpreting comparisons between manufacturers because most but not all models had available images that met study inclusion criteria. Similarly, only images of models from major manufacturers were included and results may not be generalisable to newer entrants into the ATV industry. Finally, these studies provide a starting point for optimal seat design, but additional studies including modelling using anthropometrics and vehicle dynamics may be needed to determine the best seat design based on safe adult operation and injury prevention criteria.
Conclusions
Carrying passengers and use of adult-size vehicles by children under 16 years of age are major risk factors for ATV-related deaths and injuries. Longer ATV seats make both of these risky behaviours more likely to occur. Our data show a wide variability in seat length and seat placement among 2012 model-year, adult-size ATVs. These findings illustrate the lack of industry-wide standards for ATV seat design and suggest an inconsistent use of safety considerations across the industry. Standardised criteria for model-appropriate seat length and placement should be implemented. Criteria might include starting ATV seats far enough from the handle grips to allow adequate steering by adult operators but not by children, and having the backs of seats extend no further than the rear axle or even less if the extended grip of the typical rider has been reached. Such steps would be a good starting point for improving seat design in order to encourage safer ATV use. Additional studies supported by manufacturers and by regulatory bodies could help further define optimal seat design. Ultimately, regulations may be needed to ensure that standards for safe seat design are incorporated throughout the ATV industry.
What is already known on the subject
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All-terrain vehicle (ATV) crashes are a serious health and safety concern, particularly in rural communities.
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There are numerous risk factors for ATV-related injuries, including carrying passengers and operation by youth of adult-size vehicles.
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Engineering approaches can be highly successful in promoting motor vehicle safety, but more of these approaches are critically needed for ATV injury prevention.
What this study adds
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A new methodology was applied to study seat design among adult-size ATVs from major manufacturers.
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High variability in seat length and seat placement suggests inconsistent consideration of safety criteria for optimising seat design.
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Some seats are long enough to carry multiple riders and some have seat fronts close enough to the handlebars to allow operation by children.
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Acknowledgments
The Department of Emergency Medicine provided support for these studies. We would specifically like to acknowledge Nathan Miller for developing the image-based measurement methodology. We thank our engineering collaborators who worked on and/or provided guidance with our ATV seat length and placement pilot study including John Steffen, Jonathon Marsico, Thomas Schnell (Director of the Operator Performance Laboratory at the University of Iowa Center for Computer Aided Design) and Daniel McGehee (Director of the Human Factors and Vehicle Safety Research Division at the University of Iowa Public Policy Center). We would also like to thank our colleagues at the Iowa Injury Prevention Research Center for their continued advice and support.
References
Footnotes
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Contributors CAJ conceived the study, supervised the student research assistants and co-wrote the article. GMD helped to supervise the students and write the article. She also formatted the data for presentation and performed data analysis. NSM and KT completed all the measurements reported in the study.
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Competing interests None.
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Provenance and peer review Not commissioned; externally peer reviewed.