Driving a motorized wheelchair is not without risk and requires high cognitive effort to obtain a good environmental perception to complete tasks such as obstacle avoidance and path planning. Nonetheless, completely autonomous wheelchairs release the users from any cognitive and muscular effort, resulting in a progressive degradation of their residual capacities. Thus, we developed a collaborative driver assistance system that engages selectively, specifically when it detects a positive or negative height object within a defined safety zone. The system first reduces linear speed to assist and prioritize the user in making a decision and ultimately calculates a steering direction that avoids obstacles. An extensible mathematical model is devised by relying on lidar and ultrasonic sensors. Simulations have been carried out, confirming the effectiveness of this proof-of-concept.