Passive safety measures for improved vehicle occupant safety

Key facts

• Vehicle models sold in Europe, inclusive of the UK, must meet minimum standards for the safety of occupants.
• Vehicle manufacturers must demonstrate models meet these standards by subjecting them to independently conducted and verified impact tests (commonly known as crash tests) in controlled laboratory conditions following stipulated protocols, at defined speeds and using crash test dummies.
• There are two principal impact tests currently required for cars to be sold in the EU; a frontal impact test and a side impact test. These tests, defined by UN regulations [1], are stipulated within the EU’s General Safety Regulations [2]. The GSR are the main regulations controlling the safety of all road vehicles in the European Union and govern type approval requirements.
• Vehicle manufacturers have large freedom to design vehicles however they like to meet test requirements and become type approved. Very few safety features to protect vehicle occupants in the event of a crash are specified in law. Exceptions include fitment and performance of seat belts [3] and car driver seat belt reminder warning systems [4].
• The EC is currently considering crash test improvements for occupant safety as part of its review of the General Safety Regulation. If it goes ahead, improvements are likely to be announced in 2018 [5].
• As part of the EC review of GSR, it is also considering extending the seat belt reminder requirements for car drivers to all car occupants and occupants of all other vehicles types (vans, buses, heavy goods vehicles) [6].
• Euro NCAP, a consumer-focussed organisation, has created a five-star safety rating scheme to help consumers compare the safety of cars and some light goods vehicles. Euro NCAP carries out more demanding tests than the mandatory tests and also rewards manufacturers for fitting safety features as standard [7].
• Over 85% of cars sold in the UK and elsewhere in Europe are rated highly by Euro NCAP (4 or 5 stars), proving manufacturers can easily reach standards higher than those required in mandatory tests [8].

Mandatory testing standards 

New vehicle models sold in Europe, inclusive of the UK, must meet minimum standards for occupant safety, met by passing mandatory impact tests (commonly known as crash tests) carried out or supervised by independent national testing authorities.

Different standards are set for different categories of vehicles, relating to the size, number of passengers and weight of vehicles.
These standards, and the mandatory impact test requirements, are stipulated in General Safety Regulations (EC 661/2009) (GSR). The GSR, inclusive of the regulations that have amended it (407/2011, 523/2012 and 2015/166), governs the type approval requirements for the general safety of motor vehicles, their trailers and systems, components and separate technical units [9].
The GSR (and the accompanying Pedestrian Safety Regulation (PSR) (EC 78/2009)) are the main regulations controlling the safety of all road vehicles in the European Union.

The impact tests are carried out in controlled laboratory conditions, at defined speeds and must follow stipulated protocols. The tests involve Anthropometric Test Devices (ATDs), commonly referred to as crash test dummies, which are equipped to record dynamic behaviour and predict likely real world injury.

Different types of ATD are used for front and side impact tests and record parameters (deflection, force, velocity and deceleration) to assess and ensure a vehicle is within the regulated minimum performance standards based on the biomechanical risk of injury.

To pass an impact test, dummies placed and seat belted in the front seats only of the car must record injury ‘metrics’ below stipulated thresholds during the test.

There are two tests vehicles must pass:

• a frontal impact test (UN Regulation 94); and
• a side impact test (UN Regulation 95).

Different world regions have their own standards however the European Union is actively seeking to harmonise as far as practicable with the UNECE regulatory framework (UNECE has 56 member states). Over the past 50 years Japan, the USA, Canada, South Korea and other countries have adopted their own vehicle safety requirements and standards.

Few mandatory occupant passive safety measures 

With limited exceptions, the fitting of particular passive safety features that aim to protect occupants is not specified in European law. This is because it is generally not permitted to mandate particular solutions or products. This means vehicle manufacturers have significant freedom to design their vehicles as they wish as long as they meet the occupant protection requirements in the mandated crash tests.

The few mandated passive features in the GSR for occupant safety relate to seat belts. They are:

• Seat belts and their anchorages, including fitment and testing (UN Regulations 14 and 16);
• Seat belt reminders for car drivers (but not for other vehicle occupants);
• ISOFIX (a compulsory anchor system for child restraints in cars) [10].

Commonly-fitted occupant passive safety measures 

If vehicle manufacturers only fitted seat belts, it would be difficult to pass the current mandatory crash tests, especially the frontal impact test. For example, manufacturers voluntarily fit an airbag in the steering wheel to pass the frontal impact test.

In order to pass the tests and improve occupant safety, manufacturers have implemented a variety of safety solutions including, most commonly:

i. Seat belt pretensioner Very early on in a collision, a seat belt pretensioner tightens the webbing, removing slack and ensuring that the occupant is ‘coupled’ or attached to the vehicle as soon as possible. This has the effect of providing the maximum stopping distance and subsequently lowers the seat belt forces, because the occupant changes velocity over a larger distance. Without pretensioners, some of the front vehicle structure deformation on impact occurs whilst the occupant is still travelling at the pre-impact speed within the slack of the seat belt webbing. He or she moves forward relative to the car which is being stopped by the impact, travelling into the space created by the slack seat belt webbing. In this scenario, by the time the seat belt is tightened around the occupant, the vehicle has already changed velocity and deformed, which means there is less time and distance to be restrained within and the seatbelt-induced forces on the body are higher.

ii. There are also pre-pretensioners which electronically begin to tighten seat belts if vehicle sensors start to predict a collision may happen. If a collision does not happen, the electric motor loosens the webbing to its original position.

iii. Seat belt load limiter - these devices prevent the seat belt loads becoming too great; when a threshold force is reached the seat belt webbing is released in a controlled way from the reel providing additional distance for the occupant to travel and change velocity within. Seat belt load limiters work with frontal airbags and together they manage the occupant’s energy during the impact.

iv. Frontal airbag This deploys in front of an occupant, and along with the seat belt forms a restraint system (that works together), which manufacturers design to pass the frontal crash test requirements, specifically to mitigate head and chest injury, providing particular protection to the driver from the steering column and wheel.

v. Side curtain airbag This deploys from the roof at the side of a vehicle, and can protect an occupant’s head and chest, particularly in side impact collisions and rollovers, in three ways. It can protect them from:
a. hitting whatever has impacted the vehicle;
b. hitting the side of the vehicle they are in (particularly a ‘B’ pillar (the structural part of a car between a front door and the rear seat area);
c. being ejected from the vehicle (if a vehicle rolls to one side).

vi. Crumple zones. Crumple zones are part of the exterior of the vehicle designed to deform in order to absorb the force of an impact, with the objective of leaving occupants protected in a hard shell.

Other voluntary-fitted occupant passive safety measures 

There are some additional voluntary passive safety measures that are less well known but fitted in some vehicle models. For example:

i. Steering columns that move in a crash (providing the driver with a bigger space in which to decelerate their movement forwards) 

ii. Head restraints that move in a crash to provide extra protection against whiplash 

iii. Air bags in other positions. This includes knee airbags (which help prevent femur and pelvic fractures); airbags in the base of seats (that keep the occupant tightly within their seat belt); and seat belt air bags (that distribute forces over a wider area on your body and lowers the risk of more localised force causing fractures to bones or injury to internal organs).

iv. Forgiving (softer) internal fittings (for example, dashboard made of softer plastics with underlying structures that are designed to distribute loading and avoid concentrated points which could produce high forces on impact).

Voluntarily-fitted 'adaptive restraint systems' 

Adaptive restraint systems (ARS) are additional passive safety measures (also fitted voluntarily by manufacturers) designed to adapt to the circumstances of a crash (for example the speed) and the nature of vehicle occupants (for example weight and height) and adjust accordingly the restraint loads applied. This includes providing less forceful restraint in lower-speed crashes.

These systems provide greater protection, particularly to people with more vulnerable bodies, notably older people who generally are more likely to suffer injury under given loading conditions because biomechanical tolerance to trauma reduces with age as bones weaken.

The protection of older vehicle occupants is a particular cause for concern because: they are growing in number (due to demographic changes); they are involved disproportionately in some crashes; and they sustain injuries more easily and severely than younger people. [11]

Examples are:

i. Dual-stage frontal air bags. These deploy at a tailored speed and to a tailored size, depending on the size and position of the person in the seat.

ii. Variable load limiters. These release webbing according to the collision and vehicle users’ characteristics.

Real world crashes and limitations of the current tests 

There is a phenomenon of large SUVs being purchased for use in towns and on trunk roads. It is possible that some people buy SUVs because they perceive that larger and heavier cars provide more occupant protection than smaller and lighter cars. However, the occupant protection performance of any sized vehicle in a crash is highly dependent on many variables, not just size and weight. In the real world, vehicles collide with all kinds of vehicles and static objects (road furniture, trees, telephone poles, etc.) of varying size and weight, but also at varying heights, speeds and angles. This causes vehicles and occupants to be impacted in a multitude of ways.[12]

Many crashes in the real world involve circumstances not covered by the parameters of the current mandatory crash tests.

The frontal impact test only involves a collision with part of a car’s front. This is called an “offset” test and is designed to test the structural integrity of the car. Some real world collisions involve damage to the full width of the front. These full width collisions typically generate higher deceleration forces and test the seat belts and restraint systems much more than the offset test.

The side impact test simulates a car to car impact, but the bullet or striking car is replicated by a trolley, which has uniform stiffness and only weighs 950kg. The trolley is not representative of a modern car. A modern car on average weighs more than 1,200kg and has a complicated front structure that results in concentrated forces in varying places in the event of a collision. The side impact test conditions are also very different than those experienced in impacts with poles or trees, or with collisions with larger vehicles such as heavy goods vehicles.

There is no rear impact test. 

There is no testing involving dummies in rear seats. 

Euro NCAP testing 

Euro NCAP, a consumer-focussed organisation, has created a five-star safety rating scheme to help consumers compare the safety of cars and light-vehicles.

Euro NCAP carries out more demanding impact tests than the mandatory tests. For example, it carries out a full-width frontal impact test using dummies in the front and rear of the car. It also rewards manufacturers for fitting safety features as standard, including active safety measures such as Autonomous Emergency Braking (AEB).

The Euro NCAP overall safety rating, which was introduced in 2009, is based on an assessment in four areas:
• adult occupant protection (for the driver and front seat passenger)
• child occupant protection
• pedestrian protection
• the fitting of technologies that assist safety (known as the ‘Safety Assist’ (SA) score). The SA score is determined from performance tests of today’s driver assist technologies that support safe driving to avoid crashes and mitigate injuries.
The overall safety rating used by Euro NCAP means it is possible for a car to offer reasonable protection in one of these areas, or a combination of these areas, and still be less than 4-star rated because they score poorly in other areas. Therefore, given the current scoring system, cars with a minimum of four stars and ideally five stars are recommended. Even then, a five star rating by Euro NCAP isn’t necessarily representative of a vehicle providing all-round good levels of protection in all types of ‘real world’ collisions, particularly if the stars were awarded before 2009. (The earlier star ratings only evaluated the front seat adult occupant protection and separately captured the risks posed to pedestrians or rear seat passengers.)

Euro NCAP tests provide the consumer with a useful comparison of safety performance between different cars within the same class of vehicle and that were tested at a similar time. Euro NCAP has also tested some vans and pick-up trucks, but the majority of the testing is cars.

It’s reasonable to perceive that Euro NCAP has played, and continues to play, an important role in encouraging vehicle manufacturers to elevate their vehicle safety standards voluntarily and well above the requirements of the regulated mandatory impact tests. More than 85% of cars sold in the UK and elsewhere in Europe are now rated highly by Euro NCAP (4 or 5 stars), proving manufacturers can easily reach standards much higher than those required in the mandatory tests.

The challenge is to ensure all cars sold in the UK have a minimum 4 star rating. There are still some two star cars in the UK.

The EC review of passive safety systems for vehicle occupants: and Brake’s position

The EC is reviewing the GSR and has committed to considering a number of different possibilities for extending the regulations to include more passive safety systems for occupant safety, with decisions expected by 2018.

The possibilities the EC is considering are listed in a report it published at the end of 2016 [12] preceded by a review in 2015 of the benefits and feasibility of implementation of a wider number of measures [13].

Brake’s position is to support the following measures to be legislated in 2018:

1 Seat belt reminders
The EC is considering seat belt reminders to be fitted to all passenger seats (currently only driver seats).

2 Improve frontal and side impact tests
The EC is considering the “introduction of new requirements or enhancing of existing measures in the field of …. frontal crash testing, side crash testing, rear crash testing.” [14]

Brake’s position is to support mandatory occupant testing that brings tests up to the same standard as those required to win ‘good’ (4 or 5 star) ratings in each aspect of the Euro NCAP voluntary tests.

Brake supports the following proposals for improvements to the mandatory minimum impact tests:

i) Improvements to frontal impact test, including
• Remove the exemptions for heavier cars (>2,500kg) and include Reg 94 testing for vans
• Introduce a small overlap test
• Introduce a full width test

ii) Improvements to side impact test, including
• Remove the exemptions for taller cars and include Reg 95 testing for vans
• Introduce a pole impact test
• Introduce a far side impact test

iii) Introduce rear impact testing
There is currently no rear impact test, and this needs introducing. This would verify safety standards of the fuel system (petrol, diesel, electric and hybrid) and structural integrity.

iv) Introduce testing standards that include testing with rear dummies. 

Brake supports the retention of lower impact test requirements for lightweight, smaller vehicles with lower emissions, particularly ultra-low emission vehicles or vehicles with low travelling speeds.

End notes

[1] UN Regulation 94 and 95
[2] General Safety Regulations (EC 661/2009)
[3] UN Regulations 14 and 16
[4] General Safety Regulations (EC 661/2009)
[5] EC, Saving lives: Boosting car safety in the EU, 2016
[6] ibid
[7] Euro NCAP
[8] Euro NCAP
[9] General Safety Regulations (EC 661/2009)
[10] General Safety Regulations (EC 661/2009)
[11] Richard Cuerden, Mervyn Edwards, Matthias Seidl, for European Parliament's Committee on Regional Development, The impact of higher or lower weight and volume of cars on road safety, particularly for vulnerable users: analytical study, 2016
[12] EC, Saving lives: Boosting car safety in the EU, 2016
[13] EC, Hynd, D. et al, Benefits and feasibility of a range of technologies and unregulated measures in the field of vehicle occupant safety and protection of vulnerable road users: final report
[14] EC, Saving lives: Boosting car safety in the EU, 2016

Page uploaded: March 2017 

Tags: crash technology