The braking and stability control systems provide continuous feedback to the system regarding the longitudinal and lateral acceleration and deceleration. At speeds above 30km/h, if these systems identify a critical manoeuvre, typical of a driver response to a likely collision, Proactive Occupant Protection uses electrical pre-tensioners to remove slack from the front seatbelts. By doing so, they prevent the occupants from moving to a position in which they are more likely to be injured if a collision occurs. The electrical pre-tensioners used by Proactive Occupant Protection are reversible and different from the single-use pyrotechnic pre-tensioners deployed during a crash. If no collision occurs, the electrical pre-tensioners retract and driving resumes as normal. Two levels of seatbelt tensioning are available from the system, depending on the criticality of the situation. The lower level can be disabled by the driver but the higher level always acts in highly critical situations.