What makes a car safe? – Part 1

Car safety is always a hot topic, but what actually makes a car safe? In Part One of a three-part series, we look at passive safety - or how your car protects you when you hit something.

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Car safety is always a guaranteed hot topic, but how do you actually judge the safety of a car? What does it even mean? And what can you do to make your current car safer? In the first of a three-part series on car safety, The Car Expert looks at this important issue.

Whenever road accident data is reported in the media, or in the event of a particularly ‘newsworthy’ tragedy on our motorways, the question of car safety is brought up.

The automotive industry has made some spectacular technological advances over the last century, and one of the biggest and most important areas of development has been car safety. But what makes a ‘safe’ car?

The broad umbrella of car safety is usually divided into two categories: active safety and passive safety.

  • Active safety is the car’s ability to avoid having an accident.
  • Passive safety is the car’s ability to protect its occupants once it is actually having an accident.

For example, anti-lock brakes are an active safety feature, while airbags are a passive safety feature.

Today we are going to look at passive safety.  In the next blog we will look at active safety; and in the final piece we will look at what you can do with the car you are already driving to make it safer.

Passive safety

Most people tend to associate ‘car safety’ with ‘passive safety’ – ie: how well the car crashes rather than avoiding the accident in the first place. This is not surprising, because most government regulations and high-profile programs like the EuroNCAP safety ratings concentrate heavily on how cars protect their occupants in an accident. Equipment like airbags and seat belts are heavily regulated, and cars have to achieve certain levels of performance when crashed into barriers and poles at certain speeds. Active safety systems are gradually being incorporated into EuroNCAP ratings, but the majority of the attention still focuses on slamming vehicles into solid objects.

The improvements made in passive safety over the last thirty years are staggering. Spend some time watching videos of crash tests on YouTube or www.euroncap.com (like the one above) and you will be shocked at the violence of a full-speed car crash.  And for anyone who thinks that an airbag is a big soft pillow which reaches out of the steering wheel to lovingly embrace you in an impact, you will be unpleasantly surprised to see how explosively an airbag deploys.  “Explosive” is an appropriate word, too, because your airbags and seat belts use pyrotechnics (ie – explosions) to yank your seat belt tight and trigger the airbags around you in milliseconds once you commence having an accident.  An airbag may save your life, but it may also give you a broken nose or cheekbones in the process.  A seat belt will hold you securely in place but could snap your collarbone as it does so.

Seat belts save lives (it’s not just a slogan)

Modern seat belts are a technological marvel compared to the original idea of a fixed-length belt which simply strapped you to the seat.  A 21st century seat belt will allow you flexibility to move around as you need to under normal driving circumstances, but precisely manage your movement in the event of an accident.

As a collision occurs, the seat belt rapidly pulls you back into the seat to ensure you are in the best position possible during the main phase of the impact. It will then progressively let you out again to control how quickly you (and all your internal organs) slow down as the car itself breaks up around you.  Without a seat belt, you and anyone else in the car continue moving as the car stops, which generally means hitting the dashboard with massive force or being thrown through the windscreen at high speed. Death or serious injury is far more likely, which is why it is astounding that some people still refuse to wear a seat belt.

Seat belts and airbags are designed to work very precisely together. Airbags deploy in specific directions, at specific speeds, and the seat belt makes sure you are held in the right place to benefit from that. There’s no point having an airbag go off to absorb your impact if you miss it because you were thrown around the cabin instead. Airbags on American cars are generally designed to be much bigger and more powerful than on European cars, because fewer Americans wear seat belts and the airbag has to try and stop an unrestrained occupant instead of a properly-belted one. Thankfully, seat belt usage in American has improved significantly in recent years, although it still lags behind the rest of the civilised world. In fact, in New Hampshire there is still no law requiring seat belts to be worn!

Designed to crumple

Modern cars are also designed to crumple in very specific ways, to absorb and divert as much impact energy as possible away from the cabin.  The cabin itself is heavily reinforced so it does not crumple, which is why car pillars have become much thicker in recent years, while at the same time window lines have become much higher. If you look at a car from the 1960s or 1970s, you will see it has lovely thin pillars and lots of glass all around, which is great for visibility but won’t stop anything trying to come through into your cabin. The chunky, almost armoured look of many modern cars might not be as pretty, and it definitely impedes visibility, but it will protect you much better during an accident.  Doors are heavily reinforced with smaller windows and higher windowlines, to protect you in a side impact. Fuel tanks have to be mounted in a certain way and constructed so that they don’t rupture and spill fuel everywhere in an accident to reduce the chance of fire. Headrests are carefully designed to protect your head and neck from whiplash in a rear impact.  The steering column has to collapse in a certain why so it doesn’t impale the driver in a frontal impact. The engine will break away from its mountings and slide under the car, and virtually every component on the car is designed to break in a certain way to absorb impact energy and deflect it away from the cabin.

This crumpling and energy absorption is why you still hear the old cliché that “new cars fall apart too easily” compared to older cars. That is absolutely false – older cars are far less safe in an accident precisely because they don’t crumple in a progressive and controlled manner. If that older car runs into a wall/tree/other car at 40 mph, it effectively stops instantly and all the energy is transferred to the occupants inside, so you keep moving at about 40 mph, usually into the dashboard or through the windscreen.

Crash test standards are getting ever tougher. EuroNCAP has consistently upgraded its ratings over the years, making a five-star result in a 2015 test significantly harder to achieve than a few years ago.  When looking at a car’s crash-test results, it is important to check which test protocol was used. Ratings are given for the protection of both adult and child occupants, as well as pedestrians, in the newer protocols.

All of the above is merely a glimpse into the technology behind how your car behaves in a crash. In the next part of this series on car safety, we will look at how your car helps you avoid a crash in the first place, which is where a lot of development is currently taking place.

This article was first published in November 2011, and has been comprehensively updated in July 2015 for freshness, accuracy and relevance.

A Mini undergoing a crash test
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Stuart Masson
Stuart Massonhttps://www.thecarexpert.co.uk/
Stuart is the Editorial Director of our suite of sites: The Car Expert, The Van Expert and The Truck Expert. Originally from Australia, Stuart has had a passion for cars and the automotive industry for over thirty years. He spent a decade in automotive retail, and now works tirelessly to help car buyers by providing independent and impartial advice.

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  1. Recalling my previous experience of crashes destroying cars, I am a little skeptical.

    The first was a head on crash, both vehicles doing 60mph (oncoming driver passed out drunk a second or two earlier), it undoubtedly confirmed the brilliance of seatbelts. I credit the ancient (also very heavy) model of diesel engine it was fitted with for being the difference between life and death for the light squidgy things attached to it like my wife, myself and the car body. The only thing that could’ve made it any worse would be an additional explosion to the face.

    We were prepared for the second crash. A Range Rover, complete with a seperate ladder frame chassis. The other driver had momentarily been blinded by the low winter sun. His airbag injuries weren’t too bad although it was a lower speed crash. My car was stationary. His car was squashed like a bug. His doors just opened. I doubt his car could’ve dissipated much more energy before the cabin started to deform. The suspension damage immobilised it.

    My wife, daughter, unborn baby and myself resumed our day completely unharmed. Our Range Rover had a purely cosmetic dent to rectify.

    On the way home that night, with the external temperature at -3.5 degrees, we stopped at the crash site and my wife gave the other driver my portion of fish and chips (they all ate theirs while I was driving). We received a thankyou bunch of flowers in the post!

    We were hit from the rear, there are crush cans between the bumper and chassis on the front, the rear is just unyielding steel covered in plastic and aluminium. The force of the impact had opened the sunroof blind a few inches.

    I love the seatbelts, but would happily trade airbags for a separate ladder frame chassis.

  2. Dear sir, I am siva from india, I have a new concept and designs for SUV & SEDAN type vehicles,my design concept vehicles can resist a major impact load during head to head collision of vehicles and I will help to our passengers by increasing the reactions time to drivers and others,shall I submit my design to you sir,before that please reply me for further discussion.

  3. A good overview but as often the case, the devil is in the detail. Although EuroNCAP tests have the ATD (test dummy) sat upright and all slack removed, this is hardly ever the position in ‘real world’ accidents. Although RoSPA state that there ‘should be no slack in the seat belt’ in reality there is significant slack in every day use, the slack creeping in to the lap belt after just a few minutes of driving. So although seat belts do save lives, they would save many more and reduce injury significantly if slack was removed from the seat belt so it sat across the hips and NOT across the stomach. Pretensioning devices can help but once the occupant is moving forward during a collision with just 3-4 cm of slack in the lap belt, it is impossible to get them back into the safer ‘no slack’ position. So the EuroNCAP ratings are providing a false sense of security to car buyers. It should be made clear to all that the results gained from these crash tests only apply if the occupant is sitting with the spine firmly against the seat back and with NO slack in the lap belt. So often occupants get internal organ injury from the lap belt on the soft tissue of the stomach… and even ‘submarine’ under the seat belt at higher impact speeds.

  4. What you haven’t mentioned is that all the safety kit that goes into cars these days has made them very expensive. So poorer people drive around in unsafe cars while rich fat cats get better protection.

    • It is unfortunately true that developing new safety systems is massively expensive, and that more expensive cars tend to get the latest and greatest safety systems. However, this technology does trickle down to the rest of the new car market fairly quickly and then onto the used car market shorty thereafter. If you look at the average safety rating of all new cars on sale 5 years ago compared to today, it is hugely different. Used car follow the same level of improvement, so a 3-year-old car today is goign to be safer than a 3-year-old version of the same car 5 years ago. So everyone does benefit, but obviously it takes time to filter through.

What are your thoughts? Let us know below.