With car safety technology constantly being updated and new features being launched every year, Jake Venter takes a close look at the most important safety features a car should have.
People often ask me: “What’s the safest car on the road?” I usually answer that if you tell me exactly what kind of accident you’re going to have, I may be able to name the make and model.
This answer emphasises that although a great deal of research is based on the most frequent kinds of accident, it’s a fact that no two accidents are the same. The causes, as well as the results, are often unique.
A number of manufacturers make the claim that their cars is the safest on the road, but such a bold statement is difficult to prove. What criteria should be used? Accident statistics plotted against brand names introduce uncontrolled variables such as traffic density, road surface variation and driver ability into the picture. The number and quality of the active and passive safety items on a car would be a good indication of the safety level. On that basis, Mercedes-Benz must come out on top. This company was the first to introduce crumple zones, anti-lock braking system (ABS) brakes and Electronic Stability Programme (ESP) cornering control, to name just a few of their innovations.
For close to a hundred years most people were under the impression that having an accident in a car with a strong and rigid framework was safer than in a less rigid car. The first person to challenge this perception was Béla Barényi (1907–1997), an Austrian/Hungarian engineer who was put in charge of the future development department at Mercedes-Benz in 1939. He retired from this post in 1972 and when he died, had over 2 500 patents to his name. Many of these had to do with automotive safety, and he is credited with inventing crumple zones, the non-deformable passenger cell, collapsible steering columns and many others.
Barényi realised that a rigid structure transmits the shock load that accompanies an accident almost immediately to the passengers, while a correctly designed deformable structure will crumble progressively. This will not only dissipate energy, resulting in reduced shock loads, but also slow down the transfer of these loads to the people inside the car. In many types of accidents, this slowing-down process reduces the deceleration felt by the passengers from over 40g to less than 12g (g = the acceleration due to gravity).
Cars in the 1959 Mercedes-Benz ‘Fintail’ range were the first designed with definite crumple zones at the front and rear, but the passenger cage was made as rigid as possible. Practically all modern cars have similar crumple zones.
On its own, this feature saves lives, but the level of safety is increased significantly when it is combined with passive safety items such as airbags and seat belts.
These items are the first line of defence against injuries. Airbags deploy at about 300km/h and can injure adults and kill small children. Consequently most airbags only deploy if the occupants are wearing seat belts capable of pulling the occupants backwards. Occasionally an airbag will not deploy because at present they’re mainly designed to cope with frontal and side impacts. They’re no good in the case of most rollovers or rear-end crashes.
Improving car control
Active safety items aim to make it easier for the driver to control a car. Every new model comes equipped with more of these items. The most worthwhile improvements in the last 20 years have been:
ABS brakes have made it possible for even beginners to survive emergency braking – a manoeuvre that often results in complete loss of car control. Whenever the system senses that one wheel shows a sharp reduction in speed compared to the others, it pulses the brake pressure in the hydraulic fluid line going to that particular wheel. The result is that drivers can brake as hard as they like but the wheels will not lock.
Many braking systems also employ a speed sensor inside the brake servo to sense that the driver is braking in a panic. The system then activates the brakes to the maximum extent. This system, called brake assist, was introduced because research has shown that many people panic during severe braking and do not apply full pressure to the pedal.
Wheelspin control is another spin-off that uses the speed sensors on the wheels. This applies the brakes on any wheel that rotates significantly faster than the others.
ESP goes even further. This system employs a yaw (rotation about a vertical line through the centre of gravity) sensor to determine whether the car is cornering normally or the driver is on the point of losing control. The car is then returned to the driver’s control by braking only one of the wheels.
Some of the more expensive cars are available with a number of features that improve vision. These include active rear-view mirrors, rearward-facing camera, adaptive headlamps, night vision, collision warning sensors and lane centring.
Finally, one should remember that all these extra features are expensive to develop and produce. This means that they first appear on expensive models. Once the rich people have paid for the development, these features become available on cheaper models.
Words: Jake Venter