  Overturning tractors are the leading cause of fatalities on farms. Steering
instability contributes significantly to the tractor overturning. This study
investigated tractor overturning accidents caused by the steering instability
using a driving simulator. The general commercial driving simulator CarSim
(Mechanical Simulation Cooperation, MI, USA) was used. Tractor operations on
steep passage slopes were simulated to mimic conditions present for a real
accident case reported in Japan. Simulations were performed on roads with and
without slopes. The tractor overturned only when on the road with the steep
slope. The decrease in the vertical force on the front wheel caused the
steering instability and the tractor to overturn. The steering instability
caused understeer which prevents the operator from being able to control the
tractor properly. Subsequently, the tractor overturned in the simulation. The
tractor driving simulator was capable of reproducing the steering instability
which can lead to the overturning accident.
