by Sally Colby
I want to ride on the tractor!
It’s hard for adults to refuse a child’s request to ride on a large, powerful machine. Many farm kids grew up doing just that, spending summers on the tractor with a parent or grandparent until they were old enough — or tall enough — to drive on their own.
Despite the statistics showing numerous tractor accidents involving only the driver or the driver plus one extra, too many children and adults are still the second passenger on farm equipment and mowers. What’s worse is that some adult drivers take unnecessary risks and operate tractors in an unsafe manner, often with dire consequences.
More farmers travel with farm equipment on roadways. Potentially dangerous situations include slow moving vehicles with heavy loads moving across traffic without using proper signals, wide machinery, left turns across traffic to enter narrow field lanes and swinging into the left lane to make a right turn into a field.
A litany of statistics reinforces the fact that people aren’t using tractors safely, and that extra riders simply don’t belong on tractors. A grandfather and grandson took a fun tractor ride and went over an embankment — the grandfather was killed; a tractor overturned sideways when the bucket was raised while traveling across a rough slope; and a tractor flipped onto its side when the operator was assisting a motorist with a stalled car on the side of the road. But for some reason, photos of mangled equipment and helicopters for emergency transport seen on the news and social media aren’t enough to deter tractor drivers from unsafe practices.
Dr. Aaron Yoder, formerly of Penn State University and now assistant professor in the Department of Environmental, Agricultural & Occupational Health College of Public Health at the University of Nebraska Medical Center, explains that many tractor mishaps are the result of instability. Yoder says nearly 50 percent of tractor fatalities are the result of tractor overturns, and countless other accidents are unreported.
“The tractor causes about half of all ag occupational related injuries, and half of those are rollovers,” said Yoder. “We’re looking at one-quarter of all occupational injuries that happen in agriculture.” Northeast states have higher tractor overturn incidents due to rolling terrain and the necessity for tight turns in small fields.
Tractor stability and overturns are related to center of gravity (CG). “The center of gravity (on a tractor) is typically somewhere between the operator’s ankles and knees; about 10 inches above and about 12 inches in front of the rear axle in a two-wheel drive tractor,” said Yoder. “In a four-wheel drive tractor or front wheel assist tractor, the center of gravity is further forward.”
Stability baselines are important in understanding how tractor overturns occur. Baselines are determined by visualizing a line to connect all the wheels of the tractor when the wheels are on level ground. The line connecting the rear tire ground contact points is the rear stability baseline, and the lines connecting the rear and front tire on the same side are the right and left side stability baselines.
“If the center of gravity comes outside the stability baseline, physics tells us that the tractor is going to overturn,” said Yoder. “It won’t overturn if the CG stays inside the stability baseline.” Tractors operating on slopes or going over bumps results in a change in the center of gravity. Yoder added that wide front-end tractors allow more space for the center of gravity to shift, which is why they’re more stable.
Yoder says if the tractor is moving too fast for a turn, centrifugal force becomes a contributing factor to accidents. If power is applied to the tractor’s rear wheels too quickly, the front end of the tractor is lifted off the ground, which can pull the center of gravity behind the tractor or behind the rear stability baseline. Another factor in rollovers is operators pulling loads that are not hitched to the appropriate location on the tractor.
Centrifugal force can push a tractor over when the tractor is driven too fast during a turn or during road travel. This can occur if the driver swerves to avoid something in the roadway or tries to move to the side for passing traffic. If the tractor is bouncing as it’s moving down the road and the tire turns as it hits the ground, drivers often instinctively overcorrect, but that action can lead to an accident.
Yoder explains that centrifugal force can be intensified if the CG is already closer to the side stability baseline when the tractor is being driven on a hillside. “The tractor tires can rotate,” he said. “That provides forward motion. But if for some reason the rear tire gets stuck in the mud, or sometimes people chain them to things like fence posts to pull them out, the front end of the tractor can rear up. The ‘point of no return’ happens in less than a second; typically 3/4 of a second.”
The point of no return occurs when the center of gravity is directly above the axle. “If it goes further, the tractor is going to turn over rearward and there’s nothing we can do to stop it,” said Yoder. “If we can disengage the rear axle before this happens, the front end will come back down.”
Rear overturns are more likely to be fatal than side overturns because the operator is sometimes thrown out of the way in a side overturn. “In rear overturns, you’re basically trapped,” said Yoder. “Your natural reaction is to grab the steering wheel tighter, which holds you in place.”
Yoder explains that when a two-wheel tractor is pulling a load, the rear tires push against the ground. At the same time, the load on the tractor is pushing down against the movement of the tractor. This brings up the concept of angle of pull. “The angle of pull is that angle we’re looking at from whatever we’re pulling where it contacts the ground up to the attachment point, or right on the drawbar,” said Yoder. “To prevent rear overturns, decrease that angle of pull.”
Lowering the angle of pull can be accomplished through lowering the drawbar or attachment point, or by raising the attachment point on the object being pulled. Yoder says the goal is to minimize the angle of pull with better attachment points and lengthening the tow rope, but that can be a disadvantage in certain tasks, such as pulling fence posts out of the ground.
“Unfortunately, sometimes people will attach to higher points on the tractor,” said Yoder, “which makes the angle of pull greater and a more likely rear overturn.” Yoder added that some older tractors have drawbars hooked to the three-point hitch, which can become a hazard if the appropriate stay braces aren’t in place.
When used correctly and with a seatbelt, ROPS (roll over protection system) are highly effective in preventing serious injury and death. “The rollbar keeps us in a protective zone if we have a rollover,” said Yoder. “They don’t prevent tractors from rolling over. Wearing the seatbelt definitely helps protect you more in the case of a rollover.”
If your tractor isn’t equipped with ROPS, check your state for cost-share programs.
Not worth the risk
by Sally Colby