Role of motion cues in straight-line driving of an agricultural vehicle

Driving simulators open new opportunities for research in a wide range of areas including human factors and ergonomics. The main concern regarding driving simulator research is the validity of the results. In order to obtain the same driving behaviours as those in a real world experiment, it is necessary to provide the driver with the same sensory cues that he/she uses in real world driving. Therefore, one would like to know which sensory cues are used by the human driver. This study investigates the effect of motion cues in straight-line driving of a tractor. Field experiments were conducted in which experienced tractor drivers drove a tractor in parallel swathing mode with the help of a lightbar guidance system. Driving simulator experiments were then performed in which experienced tractor drivers drove in two sessions: in one session motion cues were provided whereas in the other session motion cues were not delivered. Analysis showed that in the absence of motion cues, the drivers significantly increase their control activity and their performance deteriorates. It is also shown that drivers are unable to respond to the full range of disturbances on the tractor and the guidance system and that they automatically reduce the open-loop crossover frequency by reducing their gain, in order to avoid high tracking errors. In the presence of motion cues, drivers adopted a more relaxed driving style by reducing their gain and lead time constant. Using a multi-loop feedback control scheme it is shown that if the driver uses both tractor lateral deviation and yaw rate as feedback variables, he/she can drive the tractor without any lag or lead equalization. The results show that driving simulators for agricultural vehicles require a motion subsystem to allow valid duplication of the real field driving in parallel swathing mode. The implications of the results of this study for developers of guidance systems are also discussed.