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Autonomous Emergency Braking

What is the AEB car safety system?

The independent European New Car Assessment Programme, Euro NCAP has helped to bring about significant improvements in the design of vehicle structures and restraint systems that have made accidents much more survivable. You have a much better chance of surviving a crash in a 5 star car than in a 2 star car.

Car occupants still get seriously injured though and cars suffer extensive and expensive damage, even in relatively low speed crashes, so, encouraged by insurers, car manufacturers are working hard to exploit today's sophisticated camera and radar technology to bring you cars that can prevent many crashes from happening in the first place.

Many different primary safety – crash prevention – systems have appeared on new cars in the last few years from lane-keeping support to drowsiness warning, but the most significant of these new technologies is Autonomous Emergency Braking (AEB) examples of which include Volvo's 'City Safety' and Ford's 'Active City Stop'.

The potential for AEB is so significant that, despite the system's relative infancy, the Association of British Insurers has already announced that AEB will be taken into account in insurance group rating, so that cars with AEB fitted as factory standard equipment could now benefit from a reduced insurance group rating.

Availability update

17 different vehicle manufacturers now offer AEB.

According to Thatcham, 7% of new cars now on sale have AEB fitted as standard, while a further 17% can have AEB specified as an option.

Examples include Ford’s AEB system available on Fiesta and Focus for only £200 and Nissan's system which is standard on Accenta Premium and Tekna models of Qashqai and a £495 option on others.

Overall around 1.5% of cars in service have AEB fitted.

(22 July 2014)


What does AEB do?

Using sensors mounted behind the rear-view mirror an AEB system can work out if you're about to have a crash and apply the brakes automatically to either prevent the crash, at lower speeds or reduce its severity at higher speeds. Systems may initially warn you of an imminent collision and pre-charge the brakes or restraint system ready for use.

To reduce the risk of activation during 'normal' driving, AEB systems will tend to intervene 'late and hard', ie they will wait until it's clear that any response from the driver is too late and then apply the brakes as fast and hard as possible to try to prevent or mitigate the crash. In other words the system will intervene only once it has decided that it's too late for you to do much about it..

AEB systems are aimed at lower speed crashes and accidents involving pedestrian casualties.

  • 75% of crashes occur at speeds under 20mph.
  • 26% of crashes are front to rear low speed shunts.
  • Over 400,000 whiplash claims are made annually.
  • More than 6,000 pedestrians are killed or seriously injured on UK roads every year.
  • Pedestrian casualties account for 23% of all killed and seriously injured.

(Source: Thatcham)


A study in the USA has shown clearly that cars fitted with AEB are involved in fewer crashes than comparable cars without. The frequency of claims was significantly lower for bodily injury, first party (own car) damage and for third party (other car) damage.

The biggest benefit seen was in third party injuries – typically whiplash – where there was a 50% reduction in the number of claims from cars equipped with AEB.

Testing AEB performance

Thatcham is part of an international group developing procedures to test the performance of AEB systems in the most common types of crash seen in the real world. With test procedures agreed for some scenarios, Euro NCAP started including AEB assessment in its rating scheme from 2014.

Testing uses specially developed targets with characteristics of colour, size, light and radar reflectivity chosen to represent a real car while being softer and capable of receiving repeated impacts. Robot drivers (steering and throttle) support the test driver for accurate alignment, control and repeatability.

Different crash types

City (low speed, low injury risk but high volume)
Car approaching the back of a stationary target car at speeds from 10 to 50km/h (approx. 6 to 30mph). Tests undertaken at different approach speeds with points awarded for avoidance.

Inter-urban (higher speeds, higher injury risk, lower volume)
Car approaching a slower moving target car at approach speeds from 50 to 80km/h, and car approaching a lead vehicle that is decelerating. Tests undertaken at different approach speeds and different headways/deceleration with points awarded for avoidance and mitigation.

Pedestrian (high injury risk but smaller volume)
Pedestrian walks out from the nearside; pedestrian walks out from behind an obstruction (parked car) and pedestrian runs out from the farside. Pedestrian test targets and protocols are still being developed.

Euro NCAP AEB test – Nissan Qashqai (2014)


Insurance group rating

The insurance group rating panel, comprising members of the Association of British Insurers (ABI) and Lloyds Market Association (LMA) meets monthly to set advisory motor insurance ratings for new passenger cars in the UK.

For AEB, the panel will be taking account of performance in the 'City' test only as this addresses scenarios most relevant to insurers.

The result of the City test is based on a point score for each speed increment from 10 to 50km/h with the points available at each speed weighted to reflect crash frequency and risk of whiplash or personal injury claim. More points are available at lower speeds to reflect the frequency of whiplash claims at lower speeds, and the frequency of low speed shunts.

If the car target is completely avoided, the full point score is awarded for that test speed.

The total points score achieved in the AEB City test is translated into a percentage reduction to be applied to the parts and labour part of the group rating calculation rather than to the overall group rating calculation.

Parts and labour is the largest component in group rating, so significant reductions in overall group rating are feasible.

Factors used to calculate group ratings
  • Damage and Parts Costs – The likely extent of damage to each car model and the cost of the parts involved in its repair. The lower these costs, the more likelihood there is of a lower group rating.
  • Repair Times – Longer repair times mean higher costs and the greater likelihood of a higher group rating. Different paint finishes on modern cars are an important factor, so these too are taken into account.
  • New Car Values – The prices of new cars are taken into account as they are often a good guide to the cost of replacement and repair.
  • Parts Prices – A standard list of 23 common parts is used to compare one manufacturer’s parts costs to another. The lower these costs, the more likelihood there is of a lower group rating.
  • Performance – Acceleration and top speed are important factors. Insurers know very well, from their claims statistics, that high performance cars often result in more frequent insurance claims.
  • Car Security – Security features fitted as standard equipment by motor manufacturers can help to reduce insurance claims costs. Such features include high security door locks, alarm or immobilisation systems, glass etching, coded audio equipment, locking devices for alloy wheels and visible VIN numbers.


(Page updated 22 July 2014)