Car safety features explained

Browsing the options list of a new car, it can be tempting to opt for high-end entertainment kit and convenience-boosting technology, over advanced safety features.

While it’s never nice to think about the worst that might happen on the road, ensuring your car has the right safety features can make all the difference in an accident.

Thankfully, new cars have never been safer. Manufacturers are continually developing vehicle safety technology to not only mitigate the effects of a collision but, in some cases, avoid one altogether.

Much of this technology is included as standard, but often varies from model to model. For instance, side airbags for rear passengers are often only offered as an optional extra, so it’s worth considering carefully.

Vehicle safety kit can be classified in two ways: ‘active’, which will intervene before an accident to improve safety and ‘passive’, which operates to protect passengers once a crash has happened.

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Video: Active safety features explained

Watch our video explaining how the latest active safety technology works and why it's worth having on your new car.

Electronic stability control (ESC)

Electronic stability control, or ESC, is one of the most important recent developments in vehicle safety. ESC is software that can automatically reduce engine power and, depending on the individual system fitted, operate individual brakes, should it detect the car is about to lose stability or is at risk of a skid.

Independent studies have shown that ESC could prevent up to a third of all road accidents. It’s such an important development that manufacturers are now required by law to install ESC on all new cars.

Other acronyms used by manufacturers include ASC, DSC, DTSC, ESP, ESP+, VDC, VSA and VSC. Each may have a subtly different method of operation, but all operate to keep the car on its intended path, should the wheels be at risk of losing grip due to slippery conditions or the driver's inputs.

Autonomous Emergency Braking

Autonomous Emergency Braking (AEB) is a new, but major, leap forward in preventing vehicle collisions. Usually available as an option, but increasingly fitted as standard, autonomous braking systems use a variety of sensors and cameras to monitor the road ahead. AEB will audibly alert the driver to an impending collision. 

If the driver doesn't take any action, the AEB system will automatically perform an emergency stop to reduce the effects of the collision. At lower speeds, many automatic braking systems can prevent an accident altogether. 

If your car has AEB, you can often enjoy reduced insurance premiums over a comparable model without it.

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Electronic brake-force distribution (EBD)

This development of anti-lock brakes (ABS) automatically distributes brake force between the wheels. This helps to minimise stopping distances while bringing the car to a halt, predictably and in a straight line.

Adaptive cruise control

A development of conventional cruise control that uses radar to maintain a set distance from the car in front. 

Should that car slow down, the system will automatically reduce the vehicle’s speed to match. If the car moves out of the way, adaptive cruise control will accelerate back up to the pre-set cruising speed. 

Advanced versions even work in slow-moving traffic and can bring the car to a standstill before automatically setting-off again.

Lane-keeping technology

Basic lane-keeping systems simply warn the driver if they let the car stray too close to the edge of their lane on the motorway without indicating. This is done either through an audible warning or through haptic feedback (e.g. a vibrating steering wheel).

More advanced 'active' systems will automatically make steering adjustments to keep you within lane, though most will stop working after a couple of minutes if they detect the driver is not holding the steering wheel or making any attempt to keep the car within its lane themselves.

On some (higher-end) models, active lane keeping is often packaged along with adaptive cruise control (see below). This can alleviate the burden of long motorway journeys, but it's worth stressing the systems are meant as driver aids, and not as a form of autonomous driving.

Visibility aids

You would expect that good all-round visibility is among the first aims of any new car design. Unfortunately, with modern cars there is always a conflict between the need to strengthen the cabin to withstand serious crashes and the need to see out from the driver's seat. 

This means that modern cars tend to have poorer visibility thanks to oversized pillars, though largely compensate with cameras and/or proximity sensors to alert the driver to obstacles they might otherwise miss. 

The most advanced systems utilise an array of hidden cameras to stitch together a 'top-down' view of the car, which can make manoeuvring into the tightest of parking spots a doddle.

Speed-limiting devices

Many cars fitted with cruise control also come with a feature to prevent the car being driven above a pre-set speed. Speed-limiting devices can normally be set to any speed and will gently reduce engine power when it is reached. Many systems will deactivate if the driver floors the accelerator, so they can still react to developing situations on the road.

Smart seatbelt reminder

As a nation we’re pretty good at buckling up, but not using seatbelts is still a major factor in road traffic injury statistics. The best systems don’t just remind the driver to buckle up, they sense which seats are occupied and alert the driver if any other belts haven’t been fastened.

Attention monitoring systems

These systems monitor the driver's responses, looking for signs that might indicate tiredness. They vary between manufacturers - some sound an alarm while others vibrate the seat or give visual warnings to alert the driver that it is time to take a break.

Blind spot warning systems

Blind spot warning systems can reduce the likelihood of an accident when changing lanes by alerting drivers to unseen adjacent vehicles. This is normally done via a light in the door mirror, which is often backed up by an audible alert should the driver not see it and make an attempt to change lane.

Active headlights

Basic active headlight systems have additional lights that come on to the left or right for cornering, lighting up the bend as you go. More sophisticated systems have active beam control - linking the direction of the head lamp beam directly to the steering.

The most advanced systems not only allow the head lamps to turn as the wheels do, but use cameras to detect cars ahead. If the system senses them, it adjusts the headlight beam automatically to provide maximum illumination without dazzling other road users.

Tyre-pressure monitoring systems

Having under- or over-inflated tyres can upset the car's handling and lead to an accident. Tyre-pressure monitoring systems (TPMS) warn of incorrect tyre pressures, helping you maintain them at the correct setting.

There are two basic types - 'direct' and 'indirect' pressure monitoring. Direct tyre pressure monitoring involves the use of a sensor inside each tyre to measure the pressure and send a signal to the driver via a warning on the dashboard.

Indirect tyre pressure monitoring systems do not have sensors. Instead they use the anti-lock brake system (ABS) sensors to monitor wheel speed. If the system senses a change in a wheel speed relative to the other wheels, it calculates that the rolling circumference must have changed and assumes this is due to a change in tyre pressure.

Accidents can happen regardless of how well equipped your car is. For advice on how to handle a collision, read our guide on what to do if you have a car accident.

Active safety features quiz

Passive safety features explained

A strong body shell

The starting point for vehicle safety; a well designed car body shell resists and dissipates crash forces well and provides better protection for those in the cabin. Look for cars with a good Euro NCAP crash-test score. Check out the car’s detailed category scoring and not just the headline star rating.

Dual-stage airbags

Airbags can make the difference between an occupant receiving minor injuries and serious injury or death in a 40mph head-on crash. Sensors in the car monitor deceleration rates and then fire the airbags to cushion any impact between the occupant and the car's interior.

Dual-stage airbags have sensors that trigger different responses for crashes of different severity. For example, they inflate less rapidly in lower severity impacts, reducing the chance of airbag-related injuries, while still cushioning the impact. Sensors in the seat also take into consideration how far forward the passenger is sitting, and can inflate the airbag accordingly, to provide the best protection.

Good head restraints

Poorly designed or adjusted head restraints account for many whiplash injuries, which usually occur if you are shunted from behind.

Make sure that a car’s head restraints can be raised high enough to suit drivers and passengers of all heights – the top of the head restraint should sit level with the top of the person’s head, and the head should be no more than an inch away from the restraint when the occupant is sitting comfortably for it to be effective. Front head restraints are tested by Euro NCAP to check their resistance to whiplash injury.

Seat-mounted side airbags

These help protect the pelvis, chest and abdomen in a side-on crash. Seat-mounted side airbags are preferable to door-mounted airbags as they stay in the correct position should the seat move. Side airbags are normally fitted as standard for front-seat passengers but may only be offered as an option in the rear.

Side curtain airbags

These usually drop down from the roof lining above the windows to protect the heads of front and rear passengers in the event of a side-on crash. If you're buying a seven seat car such as an MPV, it's worth checking that the curtain airbags extend to the third row, as this varies between manufacturers.

Knee airbags

Historically, advances in car safety have focussed on crash survival, but now manufacturers pay attention to how the deformation of a car’s interior in a collision can leave passengers with life-changing injuries – particularly to the legs of front-seat occupants.

The development of the knee airbag means drivers would be cushioned from immovable objects such as the steering column and the leading edge of the dashboard, preventing injury to their lower limbs and pelvis. It’s just one of the many developments that could mean the difference between walking away from an accident and being stretchered out.

Pre-tensioned and load-limited seatbelts

Seatbelt pre-tensioners take up any slack in the belt when they detect a crash is imminent, keeping you fixed in your seat. Load limiters, on the other hand, prevent injury by allowing the belt to stretch slightly as the crash takes place so that not too much force is placed on the passenger’s body, particularly their ribcage.

Isofix child seat mounts

Isofix is a system for fitting child seats that uses mounting points built into the car seats, rather than the seatbelt. It has become the accepted standard for fitting child car seats, with nearly all manufacturers offering it, at least as an option.

The main benefit is that they make the seat easier to install, so there's less risk of getting it wrong. An incorrectly installed child car seat means it may not give full protection to the passenger in a crash. Three-point Isofix systems come with two lower anchorages, and a third anchor point which can be a ‘top tether’ or a support legs. The type you choose will depend on your car - a car with an under-floor storage cubby is unsuitable for a child seat with a support leg, for instance.

However, in crashes Isofix seats aren't automatically safer than belted seats. This is because the Isofix mounts create a stiff joint, through which crash forces are more readily transmitted to the seat shell and its occupant. With a belted seat, the compliance or 'give' in the belt allows some movement in a crash, absorbing some of the crash energy. Check out the unique Which? child car seat test results to find out which seats perform best of all in typical crashes.

We only award Best Buys to the safest child car seats. Find out which ones you should consider.

Pedestrian protection

Cars with a more ‘pedestrian-friendly’ front end should reduce the severity of injury to anyone unfortunate enough to be hit by a car – particularly at speeds of up to 30mph.

The key behind this is vehicle design that decreases the likelihood of hitting ‘hard points’ such as the A-pillars or engine block. Manufacturers have employed a variety of different technologies, including pop-up bonnets and deformable bumpers, to decrease the severity of an impact.

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