The aim of the report was to identify shortcomings and potential risks of vehicles operated by joysticks designed for drivers with severe disabilities, especially concerning the human-machine interaction. A small group of drivers with severe disabilities are able to drive a car provided it is fitted with a joystick for acceleration, braking and steering. Owing to the design of the joystick which consists of an angle-operated lever fastened at one point and the lack of natural feedback from the brake system and front (steering) wheels, the task of driving can be unnecessarily difficult and arduous. Above all three risks can be identified: 1) The lack of feedback from steering causes the driver to make faster movements of the joystick than the servo-unit can manage thus causing time delays in the steering system. 2) Since the joystick is angle-operated and the transfer function of the brake is not always optimal it may be difficult to handle the brake in a controlled and comfortable way. 3) The most obvious risk is that the accelerator/brake control and the steering control may influence each other (interference), mainly since it is not possible to provide tactile separation of the control directions of the joystick. A manoeuvring test was carried out by five joystick drivers and a control group. The possibilities of carrying out fast lateral manoeuvres and fixed controlled decelerations with the joystick were evaluated. Furthermore, a possible interference phenomenon was studied among joystick drivers. The results partly verified the identified risks, even so it was not possible to link the results to traffic safety consequences in an adequate way. Consequently, it is not known whether cars equipped with joysticks for severely disabled drivers create a risk from the traffic safety point of view. (A) The report has also been published in Swedish (VTI meddelande 860)
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