Intelligent control and human computer interaction is investigated for a powered wheelchair using a simple expert system and ultrasonic sensors. The aim is to make driving easier. Signals from sensors and joysticks are interpreted. The interpreted signals are mixed so that the systems collaborate with the human driver to improve their control over direction and speed. Ultrasonic sensors identify hazards and the system suggests a safer speed and direction. Results are presented from drivers completing a series of timed routes using joysticks to control wheelchairs both with a microcomputer and sensors assisting them and without. Recently published systems are used to contrast and compare results. The new system described in this paper consistently performed better. An additional result appears to be that the amount of support from the microcomputer and sensors should be altered depending on surroundings and situations. The research is part of a bigger research project to improve mobility and enhance the quality of life of disabled powered wheelchair users by increasing their self-reliance and self-confidence.