Tractor Rollover Fatalities in the United States
Matt Solymossy, Graduate Student
Safety 757: Principles of Occupational Epidemiology
Professor Kwangseog Ahn
April 26, 2014
Previous literature review indicates 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 known. Multiple factors may lead to increased exposure for 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 likelihood for a farm tractor rollover, and further, a farm tractor rollover fatality. This research is important because although it has been previously identified that tractor rollover fatalities are the leading cause of accidental deaths on farms, the fatality rates have not decreased significantly over the years. This is despite new technology available to protect tractor operators. In addition to supporting the hypothesis that Rollover Protection Structures (ROPS) prevent fatalities, this research will also help identify variables which led to higher prevalence of farm tractor rollover fatalities.
Tractor rollovers remain the deadliest hazard faced by agricultural workers in the United States. Some tractors are equipped with Rollover Protection Structures (ROPS), which protect the operator in the event of an overturn. In the agricultural community however, many tractors are not equipped with ROPS. According to Cole, et al., “Agricultural tractor rollovers are the leading cause of fatalities among farmers in the United States.” (2)
In the United States, there are “approximately 4.2 million tractors on farms and ranches.” (6) A poll of US farms discovered that only 51% of US agricultural tractors are equipped with ROPS. (6) This means there are 2.14 million farm 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 (5). Based on this statistic, 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% (6), 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. Crop farmers specialize in growing grain (corn, beans, wheat, etc…) for human food consumption and ethanol and biodiesel production, while livestock farmers raise animals for meat and/or dairy. 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 (6). 82% of tractor rollover fatalities occur on crop farms. Typically, crop farmers have a greater exposure to tractor accidents than livestock farmers. A livestock farmer typically does not have as many uses for tractors as a crop farmer. Livestock farmers used tractors to transport feed to the animals and only use tractors for short periods of time on predetermined routes. The routes tractors travel on for livestock farming are generally flat, and may even include gravel or dirt roads. Livestock farmers on the other hand, use tractors to plant crops, spread fertilizer, manure, and pesticides, and to harvest crops at the end of the season. On livestock farms, tractors are driven on every acre of land and often includes areas with rough and sometimes steep terrain.
Before fatality statistics are evaluated, it is important determined what causes tractor overturns and/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 exposed to an increased risk for a rollover. Appendix A (2) )(note, appendix did not copy, link copies at end of page) 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 (2)(note, appendix did not copy, link copies at end of page), it is clear that the average farm acreage in Illinois is much greater than the other 5 states with high rollover fatality rates. This could results increased hours operator 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 (6). Older operators have slower reaction times than younger workers and may not be able to sense the tractor is about to roll as easily as younger workers. Older operators are also more likely to experience injuries that are more life threatening than younger operators, who can recover from their injuries better.
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 agriculture do not have ROPS installed. In 2006, the percentage of farm tractors equipped with ROPS was only 59% (6). Some tractors are equipped with ROPS that are adjustable or removable. This is useful in low clearance situations where ROPS are inconvenient. For example, tractors used in apple orchards have low hanging branches that may interfere with a traditional stationary ROPS design. In these types of conditions, removable or adjustable ROPS are beneficial. This may include a roll bar where the operator simply removes a locking pin and folds the ROPS down. However, this can result in decreased use or nonuse of ROPS if the operator fails to re-adjust or re-deploy the ROPS (5). 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”(4).
There have been numerous initiatives conducted to prevent farm tractor rollover fatalities. 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 partial cost to install aftermarket ROPS on tractors. However, the results of this program only led to 0.6% increase in ROPS installation (6). 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 of installing ROPS 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 (6). Another initiative includes ROPS engineering improvements which have made ROPS less 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 (6). Pre-manufactured CROPS can fit on many older style of tractors from well-known tractor manufactures such Ford and Massey Ferguson (1). Unfortunately, CROPS are not available for any other tractor manufactures. 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-deploy the ROPS after leaving a low clearance situation to be protected (2).
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 (2). The main reason for this is straight economics. Smaller farms, which typically include family farms, have less resource available to invest in tractors already equipped with ROPS and to install aftermarket ROPS kits. Farm owner have also made statements similar to this at tractor safety classes, “Why would I pay for ROPS installation on my tractors when the operators don’t wear their seat belts anyway.” Evidence does support that ROPS are effective at preventing fatalities even in incidents when the operator fails to use the seat belt.
Research Hypothesis and Methods
Research proposals typically include two hypothesis, 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 (4).” In this experiment, farmers make up the group of population(s) who will be studied.
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, size of farm, income of farm, and farm location are all potential explanatory outcomes. Tractors manufactured prior to October 25, 1976 were not required to by OSHA to include ROPS. There is no mandatory standard or regulation that requires retrofitting these older tractors with ROPS. 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. 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 rollovers compared to the number of farms in the United States. This would then be compared to rates from explanatory variables previously described. This data could be used to identify the types of farms and tractors with a higher prevalence of fatalities from tractor rollovers.
As stated previously, data that would need to be analyzed for this study would include 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 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 (NASS).
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. Because any tractor manufactured prior to 1976 was not required to have ROPS, an obvious conclusion would be that overturns involving tractors manufactured prior to 1976 have a higher fatality rate in comparison to tractor manufacture after 1976. 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. This is due to the acres that livestock farmers cover on tractors in comparison to dairy and livestock farmers.
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 is that additional resources need to be allocated at campaigns ensuring farm tractors have rollover protection structures. As previously mentioned, rebate programs and educational efforts aimed at increasing ROPS use on tractors has been ineffective, resulting in less than a 1% increase in ROPS installation. By collecting data on the explanatory outcomes listed in this paper, epidemiologist could focus their efforts on the farms and farmers with the greatest prevalence of overturn fatalities. This would be more effective than previous campaigns, which targeted all farmers.
1.) (2012) Agricultural Safety: Cost-effective Rollover Protection Structures (CROPS).
Center for Disease Control and Prevention. Retrieved from
2.) Cole, H.P., McKnight, R.H., and Donovan, T.A. (2009). Epidemiology, Surveillance, and
Prevention of Farm Tractor Overturn Fatalities. Journal of Agromedicine,
3.) Friis, Robert H. (2010). Epidemiology 101. Sudbury, MA. Jones and Bartlett Learning.
4.) 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/tractor–
5.) McKenzie, E.A., Mahmood, R., Powers, J.R., and Lutz, T.J. (2008) Agricultural Safety
Systems / Implementing and Developing Industry Standards. Professional Safety.
6.) Murphy, D.J., Myers, J., McKensie, E.A., et al. Tractors and Rollover Protection in the
United States. Journal of Agromedicine, 15:249-263.