Tractor roll-over demonstrations show severity, reality of accident


ROCK SPRINGS, Pa. – Parents pushed toddlers in strollers closer to the barrier fence and pointed to their older children to watch as a New Holland tractor rolled over a hillside at Ag Progress Days last week.
No one was injured in the mock accident created by Penn State agricultural engineers, but plenty of onlookers got a feel for the importance of preventing accidents like this.
The demonstration was conducted several times daily during the event’s three-day run. Visitors crowded around to hear Penn State specialists explain how tractor rollovers can occur and how they can be prevented.
Why it happens. According to ag safety specialist Dennis Murphy, a tractor can roll over when its center of gravity moves outside the stability baseline as the machine operates.
The baselines are imaginary lines drawn between the tractor’s tires, front to back and side to side, as the tires rest on the ground.
“Anytime the center of gravity moves above a stability baseline, the tractor will fall right over from its own weight,” Murphy said.
Oh, no! The crowds’ gasps proved they were frightened or in awe as they watched the remote-controlled tractor drive across the 20-degree slope and hit a pile of dirt to simulate a bump.
In less than a second, the tractor was laying on its side, supported only by the front edge of the hood and the roll-over protective structure, or ROPS.
“Anytime you’re on a hillside, your center of gravity moves over. You’re just waiting for the high side to hit a bump or the low side to hit a washout or groundhog hole and you’re going over,” Murphy said.
Not the only way. In another demonstration, Murphy and his colleagues showed how tractors can overturn rearward from rear-axle torque or drawbar leverage.
In their demonstration, the specialists showed the tractor pulling an immobile tree stump.
When chained to the tractor’s drawbar, the stump caused the front of the tractor to raise off the ground less than a foot, and the rear tires slipped.
However, when they chained the stump to the tractor at a point higher than the drawbar, the load meant trouble.
According to a Penn State fact sheet written by Murphy, unsafe hitching at a higher point on the tractor increases tire pressure against the ground.
When that pressure is higher, the tires can’t slip as much and rear axle torque lifts the front end.
Almost always killed. A tractor can overturn before the driver has time to react.
Murphy said this type of accident almost always results in death as the tractor crushes the operator. But it doesn’t have to be that way, with a little education and the right protective equipment on the tractor.
“In three-quarters of a second you’re on your back and the rollbar stops you,” Murphy said as bystanders watched the demonstration.
“The safest place to be is in the tractor seat,” he said.
Safe zone. The dummy buckled into the seat stayed upright and was fully protected during both situations by the roll-over protective structure.
“This should really show you all the value of the ROPS,” Murphy said.
“The only way to stay in the safe zone is to wear a seat belt,” he said, noting most farmers don’t buckle up during their workday.
Murphy also notes the ROPS isn’t designed to prevent roll-overs, but to prevent the operator from being crushed during an overturn.
Satisfied. Murphy says his demonstration seemed to impact all the families who watched.
“We’ve gotten a real good response from it. We see a lot of parents explaining to their kids what we’re saying, reinforcing it and putting it in their words,” he said.
According to university statistics, three people were killed in Pennsylvania in 2003 due to tractor roll-overs.
(Reporter Andrea Myers welcomes reader feedback by phone at 1-800-837-3419, ext. 22, or by e-mail at


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