Steering columns are designed to retract during an impact by shearing some plastic pins and allowing the outer column tube to slide down the inner tube. This often happens when the driver impacts the steering wheel. To further reduce the possibility of injury, Volvo's S40 uses a pyrotechnic charge to pull the steering column away from the driver.
With 140 millimetres of travel, the steering wheel can be moved away before the driver hits it, reducing upper body injuries. Sensors in the driver's seat monitor seat position in relationship to the steering wheel and sophisticated software activates the charge to retract the steering column only when necessary. Every collision and every driver is unique. The system is designed to react differently for each situation.