Airbags are passive safety devices, designed to save occupants from injuries in the event of a crash. Modern airbags are meant to work in conjunction with seatbelts to afford additional cushioning during a vehicle collision, and are even designated as Supplemental Restraint System (SRS) for that reason. Various sensors around the car monitor the vehicle’s speed and orientation and continuously send this data to the airbag control unit (ACU). In case of an instantaneous deceleration like a crash, the ACU triggers the ignition of a gas generator propellant, which rapidly inflates a nylon bag in about 20-30 milliseconds. The airbag provides a cushioning effect and absorbs the impact which otherwise would have been felt by the occupant. They might be expensive options, but airbags have saved thousands of lives around the world.
Newton’s first law of motion states that a body in motion tends to stay in motion unless acted on by an external force. Which is why in a crash, a car’s occupant will continue moving forward. Seatbelts are designed to secure the occupant of a vehicle against harmful body movement that may result from a collision or a sudden stop. Seatbelts also absorb energy by being designed to stretch during an impact, so that there is less speed differential between the passenger's body and their vehicle interior, and also to spread the loading of impact on the passengers body. Seatbelts also play an important role of keeping the occupant in the correct place as the airbag deploys to ensure their maximum effectiveness. Most seatbelts are equipped with inertia reels to tighten the belt when pulled fast, but not to tighten when pulled slowly. Modern seatbelts with pretensioners preemptively tighten to prevent the occupant from jerking forward in a crash.
Anti-lock Braking System (ABS)
An Anti-lock Braking System (ABS) is a safety system which prevents the wheels of a car from locking up (stop rotating) while braking. During an emergency braking maneuver, if the wheels lock-up under braking, the car cannot be steered away from the impending collision. The ABS system monitors the rotating speed of a wheel and if it detects that one of the wheels suddenly slowed down (indicating an impending lock-up), eases the pressure on the brake, letting the wheels spin freely again. When the wheel starts spinning faster again, the ABS system reapplies braking pressure. This process is repeated continuously and rapidly (upto 20 times a second). ABS helps reduce braking distances on dry tarmac and especially on wet surfaces, but may slightly increase braking distances on gravel and snow. Studies have shown ABS helps reduce accidents by a large margin.
Electronic Stability Control (ESC)
Electronic Stability Control (ESC) is a system built into some of the high end cars available these days which prevents loss of control of the vehicle by applying brakes automatically as needed. When the ESC detects loss of steering control, it automatically applies brakes to to help “steer” the vehicle where the driver wants to go. Modern ESC systems also work in conjunction with the Traction Control system to limit the engine’s power to the drive wheels to assist in keeping oversteer or understeer under control. ESC systems work even before the driver is aware of any imminent loss of control. For this reason, ESC systems inform drivers by means of a dashboard mounted light or display when the system is intervening to keep the car under control. Many governments around the world are pushing towards making ESC mandatory on all new cars and by 2012, this should be be pretty much commonplace.