Car buyers are now prioritising safety more than at any time in the past. Where once it was left up to the manufacturers to provide whichever safety features they deemed appropriate, now buyer expectations dictate that no stone be left unturned. And nowhere is this more apparent than in the compact and sub-compact segments which for many years saw little safety development, this having historically been the preserve of larger "family" cars.
In the modern world however, even small-car buyers are keen on maximising the safety credentials of their ride, so what kind of safety features should buyers have at the top of their lists, and how do they work?
Well, safety features are generally divided into two categories – active and passive. An active safety feature is something that is designed to help prevent an accident. For example, ABS, ESP and TCS (see below) are all active safety features ie. they are all active prior to an accident occurring.
Conversely, passive safety features are designed to limit the effects of a collision once it has occurred. While many such features are built into the structure of the vehicle (eg crumple zones, laminated glass etc), there are also many electronic or mechanical systems that deploy as the collision is occurring (eg airbags, seatbelt pre-tensioners and active head restraints).
A great many new systems are currently under development including lane-departure and driver alertness warning systems, blind-spot monitoring systems, and even radar guided cruise control and pedestrian avoidance systems. Complicated stuff to be sure, yet all these systems will one day be available, if not the norm on mainstream cars we will use every day. For now though, these types of safety devices are still limited to high end models and so we will concentrate our attention elsewhere.
Let's start with an overview of some active type safety features. These include
Most active safety features are part of the braking system, so this is a good place to begin.
Braking in most modern cars is constantly monitored by sensors at each wheel. These sensors send information to the on-board computer which compares
the speed of all four wheels with each other, as well as the speed of the vehicle itself.
From this it can determine if one wheel is locking up (under braking) or is likely to lock up and then takes action appropriately to prevent this from happening.
The system allows maximum braking effort at each wheel until it is on the verge of locking, then temporarily releases it allowing it to regain traction,
then re-applies the braking effort again in order to arrest the car. Meanwhile maximum braking is provided to all wheels with sufficient traction and the process
of monitoring wheel speed and modulating brake pressure continues at all four corners until the car is stopped. The purpose of ABS is to shorten stopping distances
on any type of road surface, and also to allow the driver to maintain control of the vehicle under emergency stopping conditions.
(If the front wheels are locked up, the driver has no ability to steer the vehicle around an obstacle.)
On the other hand, Traction Control (TCS) is designed to limit wheelspin at the driving wheels.
Less of an issue with front wheel drive cars, excessive wheelspin on a powerful rear-drive car can cause the vehicle to spin out of control.
Either way, if the driving wheels lose traction, particularly in a fast bend, the car is less predictable and may veer off its intended course, possibly causing an accident.
The TCS therefore uses the information from the wheel sensors to detect wheelspin, then cuts engine power to manage the traction at the driving wheels.
Early ABS and TCS systems were limited to this type of functionality, but with the advent of better technology, ABS, TCS and a number of other clever systems have morphed into a far more capable and cohesive operation - ESP.
ESP (Electronic Stability Program) not only monitors braking and traction, but also the direction and yaw of the vehicle, when compared with the driver's intended direction of travel.
It sits dormant while the driver has everything under control, but if the car's heading varies from the predicted course (ie the car experiences oversteer or understeer), the ESP steps in to prevent total loss of control.
ESP uses the same wheel sensors as found in the aforementioned ABS system, however there is also a steering input sensor and a yaw sensor, which enable the system to determine where the driver intends the vehicle to go, and which way the car is actually pointing. When a potential problem is detected, the system can cut engine power (or in sophisticated systems, redirect it elsewhere) and/or apply brake pressure to one particular wheel in an attempt to bring the car back into line. Of course the driver has only the ability to brake all four wheels at one time, thus highlighting one of the main advantages of ESP.
Another advantage is the computer's ability to react extremely quickly, in most cases, before the driver even thought there was a problem. Furthermore, given that most drivers either underreact or overreact, ESP's ability to correct for driver error means it is fast becoming the must-have item for many car buyers.
Other functions built in to a typical ESP system include CBC (Cornering Brake Control) which can brake the inside wheels when traveling round a corner; EBD (Electronic Brake-force Distribution) which apportions brake effort from front to rear in such a way as to maximise the vehicle's stability under heavy brake application and EBA (Electronic Brake Assist) which increases the brake pressure in an emergency stop to shorten the stopping distance and increase the likelihood of ABS intervention (most drivers don't brake hard enough to activate the ABS). Some systems, notably those on taller SUV style vehicles, include an anti-rollover protection system which monitors the vehicle's stability in a vertical plane and acts to prevent the vehicle getting into a situation where a roll-over is likely. Some SUV's and larger passenger cars also have a trailer-sway control function.
It should be noted that not all ESP systems are created equal. They are tuned for different types of driving conditions and vary greatly in their level of sophistication. Suffice to say though, that any ESP system is better than none.
Aside from some of the relatively new active safety features mentioned earlier, that pretty much covers what most second hand cars are likely to have fitted, so let's take a look at some passive ones.
The most commonly discussed passive safety feature these days is of course the airbag. Where once having one airbag was something to crow about, now it is common to have front, side, curtain and even knee airbags.
These are designed to deploy in the event of a severe impact in order to protect the occupants from coming into contact with hard objects like the steering wheel,
windscreen pillars and dashboard, or in the case of curtain airbags, shattered glass fragments. At the heart of this concept is the cushioning effect airbags have on a rapidly moving body,
therefore slowing the rate of deceleration and minimising both external and internal injuries.
Like ESP systems, all airbags are not created equal. Airbag technology has improved dramatically over the last ten years, meaning there are many different shapes, sizes, rates of inflation, tethering (to control the shape of the front face of the inflated airbag) and sensors that detect which seats are in use.
Airbags generally operate in concert with another clever device – the pre-tensioning seatbelt. These activate by electric or pyrotechnic means in order to tighten the seatbelt against the occupant in the early moments of the impact. Without these devices, the body would move rapidly forward in the seat, until the seatbelt suddenly locks causing the body to come to an abrupt halt against the inside of the webbing. This causes the internal organs to smash into the inside of the skeleton causing them to be severely damaged. With the pre-tensioners activated, the body can take better advantage of the car's crumple zones which allow a more controlled rate of deceleration, thus helping to minimise injury. Some seatbelts also offer a feature called a load-force limiter. These basically allow a certain amount of load to be taken by the seatbelt until a load threshold is reached, at which point they allow a bit of give (like a very heavy spring) so as to prevent bruising where the body has been pressing against the webbing.
Of course, well before the advent of the SRS (Supplemental Restraint System combining airbags, seatbelt pre-tensioners & load-force limiters), cars had for decades been manufactured with specially designed crumple zones. These are energy absorbing areas within the structure of the vehicle which when subjected to an impact, deform in such a way as to absorb the crash energy. As time has gone by, these crumple zones have become more advanced, and now not only absorb, but also redirect crash energy away from the vehicle's occupants. The use of high-tensile and ultra high-tensile steel has helped to improve the crashworthiness of modern cars without adding unwanted bulk. This is achieved through the creation of a very rigid passenger safety cell which is stronger and less deformable than the front or rear crumple zones. Side intrusion beams have also been fitted into car doors since the early nineties and help keep the car's structure intact when hit from the side.
Collapsible steering columns have also been commonplace for some decades though some vehicles now also feature a detachable pedal system designed to prevent injury to the driver's feet in a frontal impact.
In the last ten years or so, an anti-whiplash system has become popular in the form of active head restraints. This is when the head-rest on front seats moves forward during a collision from the rear so that it stops the head from being forced backwards by the impact.
Many cars now feature a fuel pump shut-off system to prevent a fire or explosion after the occurrence of a collision, and some cars are even clever enough to automatically unlock any locked doors and turn the interior light on.
Safety ratings can be found for many later model cars and are provided by either ANCAP (Australian New Car Assessment Program) or its European counterpart EuroNCAP. These ratings give an indication of the strength of the car, its ability to redirect crash energy away from its occupants and therefore minimise risk of energy, and its ability to avoid the accident in the first place. Each car is scored taking into account a number of frontal, offset and side impact tests, as well as what levels of safety equipment are fitted.
Car buyers should research the safety rating of the car they intend to buy to see if it stacks up against the competition. Try looking on www.rightcar.co.nz or look up the ANCAP or EuroNCAP websites.
There are of course many more safety features built into modern cars that we haven't mentioned here, most of which we take for granted. As a bare minimum though, buyers should look for ABS brakes and at least a driver's airbag. If the budget allows, ESP is a highly valuable feature, while side and curtain airbags would be a great addition too. Aim for the latest model car you can afford - even if it has done slightly higher mileage - the rate of improvement in safety features is huge, so a car that is a few years newer may well offer a substantially higher level of protection.
When all is said and done, the best safety feature a car can have is a safe driver, so drive to the conditions, be safe out there, and try to avoid testing out those airbags.
