Tractor Rollover Fatalities in
the United States
Matt Solymossy, Graduate Student
Safety 757: Principles of Occupational Epidemiology
Professor Kwangseog Ahn
April 26, 2014
Tractor Rollover Fatalities in the United States
TABLE OF CONTENTS
Abstract……………………………………………………………………………………………………………………………………..3
Introduction……………………………………………………………………………………………………………………………….4
Hypothesis and research Methods…………………………………………………………………………………………….8
References……………………………………………………………………………………………………………………….……..11
Appendix A………………………………………………………………………………………….…………………………………..12
Appendix B…………………………………………………………………………………………………………..………………….13
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Tractor Rollover Fatalities in the United States
Abstract
There is plenty of documentation that proves that rollover protection structures on
agricultural tractors prevent fatalities in tractor rollovers. However, the exposure for tractor
rollover fatalities in the United States is less know. Multiple factors may lead to increased
exposure to a farm tractor rollover fatality. This paper proposes a cross sectional study to
examine what explanatory variables led to the outcome of a farm tractor rollover fatality. It is
proposed that historical data on farm tractor rollover fatalities is examined to determine the
“at risk variables” which increase the likely hood for a farm tractor rollover, and further, a farm
tractor rollover fatality. This research is important because although it has been identified
decades ago that tractor rollover fatalities are the leading cause of accidental deaths on farms,
the fatality rates have not decreased significantly. This research will help identify locations with
the highest prevalence of farm tractor rollover fatalities.
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Tractor Rollover Fatalities in the United States
Introduction
Tractor rollovers remain the deadliest hazard faced by agricultural workers in the United
States. Some tractors are equipped with Rollover Protection Structures (ROPS) that protect the
operator in the event of an overturn. In the agricultural community however, most tractors are
not equipped with ROPS. According the Cole, et al (1), Agricultural tractor rollovers are the
leading cause of fatalities among farmers in the United States.
In the United States, there are “approximately 4.2 million tractors on farms and
ranches.” (5). A poll of US farms discovered that only 51% of US agricultural tractors are
equipped with ROPS (5). This means there are 2.14 million farms tractors operating in the
United States without any rollover protection. There are roughly 100 fatalities per year that
result from tractor rollovers. The United States Bureau of Labor Statistics (BLS) reported that
of the 2,869 agricultural fatalities caused by tractor accidents between 1992 and 2005, 1,412
were the direct result of tractor overturns or rollovers (4). Approximately 49% of agricultural
fatalities are caused tractor rollovers. Compare this to the second leading cause of agricultural
fatalities, which is stuck by or entanglement in other machinery at 18% (5), and it is obvious
that tractor rollovers are by far the greatest hazard in the agricultural community.
All types of farms in the United States utilize tractors for multiple tasks. Tractors are
used to plant seed, cut hay, transport feed to animals, harvest crops, and transport crops to
market. Although tractors are used on multiple farm types, research shows that a greater
hazard exists for crop farmers when compared to livestock farmers. From 2003 to 2007, the
fatality rate for tractor overturns on a crop farms was 7.2 per 100,000 workers. During the
same time period, the fatality rate was only 1.3 per 100,000 workers for livestock farms (5).
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Tractor Rollover Fatalities in the United States
82% of tractor rollover fatalities occur on crop farms. Typically, crop farmers have a greater
exposure to tractor accidents than livestock farmers. Crop farmers utilize tractors work soil,
plant seed, spread fertilizer and manure, and harvest crops on hundreds to thousands of acres
on varying terrain.
Before fatality statistics are evaluated, it is important determined what causes tractor
overturns or rollovers. There are a number of factors that increase the chance of a tractor
rollover. Some these factors include farm topography, age of the tractor, and age of the tractor
operator. For topography, the slope of the terrain is important. Farms located on terrain with
steep slopes are at a greater risk of having and overturn. Appendix A (pg. 13) shows a map of
tractor overturn fatality rates. States in the Appalachian Mountain Range (Pennsylvania, Ohio,
West Virginia, Kentucky, and Tennessee) have the highest rate of tractor overturn fatalities, at
greater than 9.8 deaths per 100,000 workers annually. Appendix A also clearly shows that
farms on relatively flatter terrain have a smaller rate of rollover fatalities. Illinois is an outlier.
Examining % farms <180 acreage on Appendix B (pg. 14), it is clear the average farm acreage in
Illinois is much greater than the other 5 states with high rollover fatality rates. This could result
in greater exposure time on tractors. Next, older tractors have a higher center of gravity and
more prone rollovers than newer tractors. Older operators are also more likely to rollover a
tractor than younger operators. Tractor operators age 75 and older have a fatality rate of 17.8
per 100,000 workers, while operators age 25-34 had a fatality rate of 0.9 per 100,000 workers
(5).
There are a number of factors that increase the probability that an overturn will lead to
a fatality. The obvious factor would be absence of ROPS. Many older tractors used in
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Tractor Rollover Fatalities in the United States
agriculture do not have ROPS installed. In 2006, the percentage of farm tractors equipped with
ROPS was only 59% (5). Some tractors also have ROPS that are adjustable or removable. This
is useful in low clearance situations where ROPS are inconvenient. For example, tractors used
in apple orchards with low clearances have ROPS that can be removed so it does not interfere
with the low branches of the trees. However, this can result in decreased use or nonuse if the
operator fails to re-adjust or re-install the ROPS (4). It’s also important to note that ROPS do
not prevent all fatalities when an overturn exists. Barbara Marlenga, a research scientist at The
National Farm Medicine Center states, "When used with a seatbelt, ROPS are 99 percent
effective in preventing injury and death in the event a tractor overturns. Even if the seatbelt is
not used, ROPS are 70 percent effective"(3).
There have been numerous initiatives conducted to prevent farm tractor rollover
fatalities, none with impressive results. These include financial initiatives, educational and
marketing programs, and engineering advances in ROPS design. In the state of Virginia, a
decade long financial initiative was conducted by the Virginia Farm Bureau that reimbursed
farmers for some of the cost to install aftermarket ROPS on tractors. However, the results of
this program only led to 0.6% increase in ROPS installation (5). The state of New York
attempted a social marketing campaign aimed at educating farmers on the cost/benefit of
installing ROPS on tractors. The social marketing campaign in New York State also included a
rebate program. Even though the cost/benefit analysis showed the cost would be saved in year
3 of the program, farmers still did not go out and install ROPS at an astonishing rate. The social
marketing campaign in New York concluded with only a 0.9% increase in ROPS installation (5).
Another initiative includes ROPS engineering improvements which have made ROPS less
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Tractor Rollover Fatalities in the United States
expensive and more effective. Cost Effective Rollover Protection Structure (CROPS) are an
aftermarket ROPS that can be purchased and installed by the farmer. Traditional ROPS costs
an average of $900 dollars, while CROPS cost approximately one third of that (5). Engineering
improvements have also been made to increase ROPS usage in low clearance situation.
AutoROPS were developed to provide low tractor clearance along with 100% rollover
protection. AutoROPS is a ROPS design that is compressed down to the shoulder height of the
operator. A sensor on the tractor trips springs in the ROPS that deploy the roll bar when a
rollover occurs. On tractors equipped with AutoROPS, the operator does not have to re-adjust
or re-install the ROPS to be protected (1).
Numerous factors need to be evaluated to determine why Farmers do not install ROPS.
The cost of installing ROPS is the major factor. Farms that are smaller in total acreage, produce
less in total annual sales, and family farms are at a greater risk of tractor rollover fatalities (1).
Reasons for this include smaller family farms are less likely to have formal tractor operator
training programs and operate older tractors without ROPS. Small family farms have fewer
resources to allocate towards tractor safety.
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Research Hypothesis and Methods
There are two hypothesis that need to be stated in research proposals, the null and
alternative hypothesis. For this proposal, the null hypothesis is that professionally
manufactured and installed rollover protection structures (ROPS) do not prevent farm tractor
rollover fatalities. The alternative hypothesis is professionally manufactured and installed
rollover protection structures (ROPS) prevent farm tractor rollover fatalities.
Information that would be required to conduct this experiment can all be found using
historical data. To conduct this scientific study, the cross sectional method of epidemiological
research will be utilized. Cross sectional studies “examines the relationship between diseases
(or other heath related characteristic) and other variables of interest as they exist in a defined
population at one particular time (2).” In this experiment, farmers make up the group of
population(s) who will be studied. This group could be broken down into other subgroups for
more detailed analysis as well. For example, farmer could be broken down into the following
subgroups: Dairy farmer, livestock farm, and crop farmer. These different subgroups have
different needs and usage of tractors and varying exposure to rollover accidents based on
length of usage, usage tasks, and usage terrain.
Using this model of an experiment, the outcome variable is easy to identify. The
number of fatalities resulting from farm tractor rollovers is the outcome variable. The
explanatory outcome(s) are more difficult to identify. Age of tractor, age of tractor operator,
type of farm, size of farm, income of farm, and farm location are all potential explanatory
outcomes. Older tractors are not required to have ROPS and so there more exposure to injury
and death in a rollover. OSHA regulation required manufactures to include ROPS with every
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Tractor Rollover Fatalities in the United States
tractor manufactures on October 25, 1976. For this reason, older tractor would be defined as
any tractor manufactures in 1976 or earlier. Annual income of the farm would be important to
know as well. Farmers with less money cannot afford newer tractors with ROPS, or afford to
retrofit there existing tractors. If separating farmer into subgroups, the type of farm where a
rollover occurred is important to know. This way comparisons could be made between the
farm types to show which farmer has the greatest risk. Location of the farm is important
because of the terrain the farm lies on. Steeper terrain increases the likelihood that a tractor
rollover will occur.
Statistics would need to be used to analyze the data that is collected in this cross
sectional study. A good start would be to find the rate of farm tractor rollovers in the United
States. This simply gives us a baseline of the average amount of tractor rollover compared to
the number of farms in the United States. This would then be compared to rates from
explanatory variables previously described. By comparing the rates from farms with old
tractors, older operators, farms with low annual income, farm location, and type of farm, the
areas/types of farms with the greatest exposure would be identified.
As stated previously, data that would need to be analyzed for this study would all be
historical data. This information would include: number of farms in the United States, number
of tractors on farms in the united states, number of tractor rollovers in the United States, the
outcomes of those tractor rollovers (did it result in a fatality), and the whether or not the
tractor involved in the rollover was equipped with ROPS. The number of farms in the United
States can be found looking at the annual United States Department of Agriculture census. The
number of tractor rollovers and the outcomes associated with them can easily be found looking
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Tractor Rollover Fatalities in the United States
at the Bureau of labor Statistics annual Census of Fatal Occupational Injuries report.
Information on the number of tractors in the United States or whether or not the tractors were
equipped with ROPS is estimated using phone surveys by the United States Department of
Agriculture’s National Agricultural Statistics Service.
Outcomes can be predicted from the explanatory variables in this study. First, it can be
predicted that the rate for tractor rollover fatalities is higher for older tractors. Any tractor
manufactured prior to 1976 was not required to have ROPS. Because of this, an obvious
conclusion would be that older tractors do not have ROPS, so the fatality rate in rollovers is
higher. Next, Tractors on farms with low annual income will also have a higher rate of fatalities
than farms with higher annual income. Farms with less monetary resources are less likely to
invest in newer tractors with ROPS or install aftermarket ROPS on their tractors. It could also
be predicted that farms located on steep terrain will have a higher rate of rollover fatalities.
Tractors generally do not rollover on level ground. The steeper the terrain, the more likely that
a tractor will rollover. Predicting whether a dairy farmer, livestock farmer, or crop farmer
would have a higher rate compared to the other is more difficult. All these types of farmers use
tractors for one job or the other. It may be predictable that of the three farm types described,
the crop farmer would have the greatest exposure.
Historical research supports that professionally manufactured and installed rollover
protection structures (ROPS) on agricultural tractors reduces fatalities. Assuming that the
experiment is conducted without any errors, the predicted outcome would reject the null
hypothesis, rollover protection structures (ROPS) do not prevent farm tractor rollover fatalities.
Therefore, the alternative hypothesis would be accepted. The conclusion from this hypothesis
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is that additional resources need to be allocated at campaigns ensuring farm tractors have
rollover protection structures. This could include programs to help pay for installation of ROPS,
educational campaigns, or increased government regulation requiring ROPS on all tractors.
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References
1.) Cole, H.P., McKnight, R.H., and Donovan, T.A. (2009). Epidemiology, Surveillance, and
Prevention of Farm Tractor Overturn Fatalities. Journal of Agromedicine,
14:164-171.
2.) Friis, Robert H. (2010). Epidemiology 101. Sudbury, MA. Jones and Bartlett Learning.
3.) Marshfield Clinic, Wisconsin Doctors, Healthcare, Medical Research. National Farm
Medicine Center | Tractor Safety | Agriculture Safety | Roll Over Protection .
Retrieved from http://www.marshfieldclinic.org/news/news-articles/tractorsafety-program.
4.) McKenzie, E.A., Mahmood, R., Powers, J.R., and Lutz, T.J. (2008) Agricultural Safety
Systems / Implementing and Developing Industry Standards. Professional Safety.
5.) Murphy, D.J., Myers, J., MeKensie, E.A., et al. Tractors and Rollover Protection in the
United States. Journal of Agromedicine, 15:249-263.
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Appendix A (1)
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Appendix B (1)
pg. 14