Manufacturers take care to ensure that their safety systems are effective for occupants of different sizes and for those sitting in different positions. However, the very best levels of protection can be achieved when the interaction between occupant and restraint systems is optimised. Several manufacturers have developed systems designed to allow a vehicle's protection systems to operate most effectively during an impact.
Some of these systems react immediately following or during the impact to optimise occupant safety. For example, they may not directly restrain the occupant but may control the occupant's movement so that the restraint systems work most effectively.
Other systems may predict when an accident is about to happen and in a split second prepare the vehicle and its occupants for the collision. Predicting the accident can be done in a number of ways: vehicle dynamics and driver actions can be monitored for panic reactions, or radar sensors can detect obstacles in front of the car. The actions which the systems take can also vary but, typically, slack will be removed from seatbelts, seating positions may be quickly adjusted to optimise airbag performance and windows shut to prevent ejection. In such cases, the actions taken are reversible in the event that the accident is avoided.