A seat belt, sometimes called a safety belt, is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision or a sudden stop. As part of an overall occupant restraint system, seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle or other passengers (the so-called second impact) and by preventing the wearer from being thrown from the vehicle.

An air bag, A.K.A. a Supplementary Restraint System (SRS), an Air Cushion Restraint System (ACRS), or the Supplemental Inflatable Restraint (SIR) (reflecting the air bag system's intended role as a supplement to conventional restraints such as seatbelts) is a flexible membrane or envelope. Air bags are most commonly used for cushioning, in particular for rapid inflation in the case of an automobile collision. Air bags are designed to compliment conventional restraints such as seatbelts and seatbelt pre-tentioners, not replace them. The number of lives saved by airbags is hard to pin down. One study, cited below, puts the number at just under 400 per year (6,000 total), and another study indicates that air bags reduce fatalities by 8% when seatbelts are worn.

(Taken from Wikipedia http://en.wikipedia.org/wiki/Air_bags) 

Active safety

To make driving safer and prevent crashes from occurring, and also to better protect occupants during a crash, cars may have the following active safety features:

• Turn signals and brake lights, including Center High Mounted Stop Lamps (CHMSL)
• Rear end Collision Warning Lamps senses deceleration of lead vehicle and flashes amber warning strobe rearward to warn following vehicles of a pending braking or stopping event
• Variable assist power steering allows assistance to the motorist while parking, but reduces steering effort assistance at motorway speeds
• Headlight wipers/washers
• Mercedes style ribbed tailights to prevent snow and grime build-up
• Dynamic steering response (DSR) corrects the rate of power steering system to adapt it to vehicle's speed and road conditions.
• Traction control (TCS) actuates brakes or reduces throttle to restore traction if driven wheels begin to spin.
• Hill holder.
• Four wheel drive (AWD) with a center differential. Distributing power to all four wheels lessens the chances of wheel spin. It also suffers less from oversteer and understeer than front wheel drive, but more understeer than rear wheel drive.
• Reverse backup sensors, which alert drivers to nearby objects in their path, are installed in some high-end vehicles, but may also be purchased separately.
• Electronic Stability Control (ESC, also known by ESP and other numerous manufacturer-specific names). Uses various sensors to intervene when the car senses a possible loss of control. The car's control unit can reduce power from the engine and even apply the brakes to prevent the car from understeering or oversteering. See car stability
• Lateral Support : Lane Departure Warning System (LDWS).
• Directional headlights, which allow the driver to see obstacles ahead in the roadway while cornering.
• Low center of gravity and other conventional features promoting good car handling and braking, and helping to avoid rollover.
• Comfortable suspension and seating to avoid accidents from driver fatigue.
• Large (relative to weight) high performance tires, suited to the weather and road conditions, contribute to braking and handling. Soft high histeresis rubber, tread and cord design are important. See Run flat tire.
• Visibility for the driver, mirrors, elimination of blind spots and possibly other awareness aids such as radar, wireless vehicle safety communications and night vision.
• Death Brake; there is a move to introduce deadman's braking into automotive application, primarily heavy vehicles, there may also be a need to add penalty switches to cruise controls.
• Four wheel steering gives, at the cost of mechanical complexity, quicker, more accurate maneuvers at high speed and/or decreased turning circle at low speed. It may also help stability.
• Adaptive cruise control (ACC).
• AWAKE and intelligent car features.
• Precrash system
• Seatbelts might also play a minor role in active safety by keeping (via locking of the inertial reel) the driver firm on his/her seat in a high-g turn or deceleration. This has been further developed and patented by Mercedes-Benz in the PreSafe™ technology which provides a synergy between active and passive systems, helping the driver avoid a danger and preparing him/her for an imminent crash.

• Brakes
  • Anti-lock braking system (ABS)
    • Electronic brakeforce distribution (EBD)
    • Cornering Brake Control (CBC)
  • Emergency brake assist (EBA)
  • Brake assist system (BAS)
  • Forward Collision Warning System (FCW)
  • Lane Departure Warning System (LDW)
  • Dynamic Brake Control (DBC).
  • Inboard brakes allow large fade resistant discs or drums, without contributing to unsprung weight and wheel bounce, which degrade braking, handling and ride, and increase mechanical loads.
   Passive safety
  
  

  
  

  Ferrari F430 drivers steering wheel with airbag.

  When a crash is imminent, various passive safety systems work together to minimize injury to the individuals involved. Much research has been done using crash test dummies to make modern cars safer than ever. Recently, attention has also been given to cars' design regarding the safety of pedestrians in car-pedestrian collisions. Proposals in Europe would require cars sold there to have a minimum/maximum hood (bonnet) height. From 2006 the use of "bull bars" (known as "roo bars" in Australia), a fashion on 4x4s and SUVs, became illegal.

• Seatbelts (or safety belts) absorb energy and limit forward motion of an occupant, and help keep occupants from being ejected from the vehicle.
• Airbags: There are many types of airbags, all of which should be considered supplemental restraint systems (SRS), used in addition to belts.
  • Front airbags inflate in a medium speed head on collision to cushion the impact of the head to the steering wheel (driver) or dashboard to the (front passenger) .
  • Side airbags inflate in a side impact (T-bone) collision to cushion the torso and sometimes the pelvis and head.
  • Curtain airbags protect the head and upper body of passengers in a side collision. Newer models may stay inflated for a longer period of time, and may help to keep unbelted occupants in vehicle during a rollover, but should be considered supplemental to belts and never used in place of belts.
  • Knee airbags inflate in frontal impact collisions to protect the driver's knees and are now available in many newer high end model vehicles.
• Crumple zone technology absorbs the energy of a collision by displacing the impact of a crash and diverting it from the internal (passenger compartment) critical structure of the vehicle.
• Side impact bars for protection against side on collisions
• Collapsible steering column, sometimes provided with steel sheet bellows.
• Crash compatibility can be improved by matching vehicles by weight and by matching crumple zones with points of structural rigidity, particularly for side-on collisions. Some pairs of vehicle front end structures interact better than others in crashes.
• Cage construction is designed to protect vehicle occupants. Some racing vehicles have a tubular roll cage
• Reinforced side door structural members
• Fuel pump shutoff devices turn off gas flow in the event of a collision for the purpose of preventing gasoline fires.
• Active pedestrian protection systems [4].
• Driver State Sensor - Research, Utilizing cutting edge video processing technology, the system remotely and unobtrusively measures 3D head pose and eyelid motion parameters of the driver.
• Padding of the instrument panel and other interior parts of the vehicle likely to be struck by the occupants during a crash. Whilst largely being supplanted by airbags, it still plays an important role in preventing injuries.