Passive safety measures on cars for vulnerable road users

Passive safety measures on cars aim to mitigate the consequences of a crash (reduce outcomes of death or serious injuries). These measures aim to either help occupants or people outside the car. This fact sheet explores passive safety measures that aim to protect people outside the car on foot, bicycles, other non-motorised transport, and motorcyclists. Collectively, these road users are often described by road safety professionals as vulnerable road users (VRUs).

VRUs: risk and casualties

Due to size, weight and rigidity, a collision between a vehicle and a human body can have catastrophic consequences at any speed. Statistics show VRUs are disproportionately casualties in road crashes compared with people inside vehicles.

Just over half the deaths on roads in Britain are VRUs. Of the 1732 road deaths in Britain in 2015, there were 409 deaths on foot; 100 cyclist deaths and 365 motorcyclist deaths [1]. More people die on foot than cycling for reasons including large numbers of pedestrians in towns (inclusive of children and adults with impairments) and low levels of cycling.

The Department for Transport calculates that, per billion miles travelled across the British road network, for every car occupant who dies, more than 8 pedestrians die. The rates are higher for cyclists and motorcyclists. For every car occupant who dies, more than 21 cyclists die and more than 24 motorcyclists die [2]. A factor contributing to higher death rates of people on bicycles or motorcycles compared with on foot is use of higher speed roads.

What happens in a collision between a vehicle and a VRU? What we do, and don’t, know

Most pedestrian injuries are lower limbs [3]. Less than one in seven pedestrian injuries occur from contact with the windscreen (usually the head hitting the windscreen) [4] [5].

However, it is known that most (eight out of ten) deaths and serious injuries of pedestrians are caused by head injuries, and most of these (eight out of ten) are in collisions with the windscreen [6] [7].

In a collision between the front of a normal saloon-style car and a pedestrian, the car can hit the pedestrian’s leg, causing the pedestrian’s body to rotate towards the car at the ‘bonnet leading edge’ (the angle between the vertical bumper and the horizontal bonnet top, known as the BLE), slide up the bonnet and hit their head and upper body on either the bonnet, the windscreen or an A pillar (the solid frame of the car at either side of the windscreen).

Increasingly, modern saloon-style cars have longer, angled windscreens and shorter bonnets than in the past, increasing likelihood of head impact with either the windscreen or the A pillar. However, not all cars are this shape. Notably there has been a significant divergence in the height of BLEs among different car models. SUVs have typically much higher BLEs. SUVs in Europe have increased from less than one in 10 cars ten years ago to around one in five today [8].

It is not known how diversity in shape of cars or any other aspect of their design and road use (for example speed) has specifically affected real world injuries of VRUs, due to lack of close investigation and collation of large data sets regarding what happens in these crashes. Information collated by enforcement agencies is inadequate to inform vehicle engineers about what happens in real world VRU collisions.

For example, it is only hypothesised that, in collisions with children and small adults, a high BLE may hit heads and upper bodies and not result in the person rotating and sliding up onto the bonnet.

Academics have called for a pan-European collision investigation programme (similar to a programme in the US [9]), to “inform the development of applicable and cost effective policies, technologies and solutions to prevent future loss of life and injury on our roads.” [10]

EC regulation of passive safety measures on vehicles to mitigate VRU injuries

The EC introduced, in 2009, regulation aimed at mitigating crash outcomes for VRUs. Commonly known as the Pedestrian Protection Regulation (78/2009) (PPR) [11], the regulation currently requires car manufacturers to do the following with regard to passive safety:

1. fit new models with bonnets and bumpers that can be described as “energy absorbing”

2. pass mandatory impact (crash) tests to the front of the car in laboratory conditions colliding the car and an ‘impactor’. The impactors are dummy body parts. The test results must meet ‘injury-based performance limits’ to pass (in other words, when the impactors and the vehicle collide, the damage incurred to the impactors mustn’t be over given thresholds). The mandatory crash tests are currently:
a. a lower leg form hitting a bumper
b. an adult’s head form hitting the bonnet in the “adult zone” (place it is likely to hit)
c. a child’s head form hitting the bonnet in the “child zone”
For the head form impact tests, two impactors are used at 35kph. The child and adult head forms have a mass of 3.5kg and 4.5kg respectively to represent a child’s head (or small adult’s head) and adult head.

The different head forms are used to impact in different “zones” (places on the bonnet where the heads are thought more likely to land.) The adult head form test is not carried out on short bonnet tops (where the measurement from the ground at the front of the vehicle to the windscreen edge is 1.7metres or less) because it is estimated the adult head form would, on these cars, hit the windscreen not the bonnet.

3. undertake ‘monitoring-only’ impact tests, conducted similarly, but with no requirements for the car model to pass the test (in essence these tests are to give the EC information to inform the feasibility of future mandatory test requirements). Monitoring-only crash tests are currently:
a. an adult's upper leg form hitting the BLE*; and
b. an adult's head form hitting a windscreen.
*An adult upper leg form is used in the BLE test because the BLE test was designed originally in the 1980s, when SUVs were not common and many cars had similar, lower bonnet leading edge heights, often about at the height of an adult upper leg.

 vru collision test zones

Figure 1: The four test procedures used in EU legislation to assess a car’s pedestrian protection.
Credit: Cuerden et al 2016

High failure rates in the ‘monitoring-only’ tests and review of the EC regulation

The PPR is currently under review alongside a review of another set of vehicle safety regulations (the General Safety Regulation (GSR)). Changes to the PPR and GSR are anticipated in 2018.
Two reports relating to these reviews have been published by the EC, one in 2015 and one in 2016.
The 2015 report [12] outlines the benefits and feasibility of various possible safety measures, including passive safety measures to mitigate VRU injuries. It also reports on the poor results of the monitoring-only pedestrian impactor crash tests.

Out of 323 vehicles subjected to the monitoring-only tests for a head form hitting a windscreen, and an adult’s upper leg form hitting the BLE, only one vehicle (a super mini) passed both tests [13].

Regarding the bonnet leading edge test, only two vehicles met the test threshold for injury levels sustained to the upper leg form, and these were both cars with low bonnets (small sports car design) [14].

Regarding the windscreen test, more than half (54%) vehicles tested failed [15].

The 2016 report [16] explains what the EC is considering taking forwards to improve safety. In relation to passive safety measures for VRUs, it says it
“foresees the introduction of ….. head impact protection on A-pillars and front windscreen” [17]

The 2016 report does not mention the BLE test.

Opportunities for change within the PPR

As well as keeping the mandatory lower leg form to bumper and head forms to bonnet tests, the EC has options, in its PPR review, to:
• mandate more crash tests (including the ones it requires for monitoring-only) and
• introduce additional monitoring tests.

Opportunity for a mandatory windscreen test

The EC has the option to elevate the “monitoring only” test of an adult head and a child head against a windscreen to a mandatory test. While more than half models submitted to the monitoring-only windscreen test failed it, nearly half passed it, demonstrating that it is possible for manufactures to meet the test’s requirements.

The 2015 report says manufacturers can address factors relating to the central windscreen area’s “stiffness” upon impact with a head. These factors include windscreen angle, shape, thickness and the glue bonding the windscreen to the car and distance to dashboard. The dashboard itself can also be addressed to be more forgiving [18].

There are also possibilities to make the test tougher by elevating its speed from 35 km/hour. It has been estimated than just over half pedestrians suffer head injuries at impact speeds below 40 km/h but frequency increases to 85.3% at speeds above 40 km/h [19].

Opportunity for a monitoring-only or mandatory A pillar test

The EC has the option to introduce a monitoring-only, or mandatory, crash test of head forms hitting A pillars.
Making A pillars more forgiving is challenging, but an obvious mitigation measure is external air bags. Some manufacturers already fit external air bags to some A pillars (for example, Volvo). The 2015 EC report says: “It will not be easy to meet a stringent …. requirement without adopting a deployable protection system [air bags]. Such systems are available.” [20]

Opportunity for improved and mandatory Bonnet Leading Edge tests of upper legs and development of a BLE to head form test

The EC has the option to make the current monitoring-only BLE crash test (which collides the BLE with an upper leg form) mandatory.

Despite some BLEs now being higher due to SUVs, the current BLE crash test is still appropriate for some older-style cars with low BLEs. Also, the test has been designed to a degree to account for differences in BLE height by testing at different speeds (vehicles with higher BLEs are tested at faster speeds to attain the same rotation speed of the upper leg form when it hits the BLE).

Given that most pedestrian injuries are still lower limbs [21], there is a strong argument for continuing with an improved version of the BLE test and mandating it. The test could be updated in line with the BLE test [22] undertaken by Euro NCAP (the consumer focussed organisation that operates a five-star rating of cars’ safety largely through crash testing.)

However, factors that weigh against the probability of the EC mandating the BLE test include: the test’s limitations (not reflective of full divergence in BLE heights); the comprehensive failure of vehicle models to meet the standards of the monitoring test; and the fact the BLE is not mentioned in the 2016 report.

The EC also has the option to work to devise a new test that tests a high BLE against a child head form and thorax (central body area) form. No such test is available at present.

It is possible to construct BLEs in ways that are more forgiving to heads. This can be achieved through use of materials that deform easily under pressure, displacing the head into the structure of the vehicle, rather than hard materials that cause the head to stop suddenly. The BLE can also be fitted with external air bags.

The EC’s 2015 report says there is a “potential benefit for head, thorax and abdomen protection for children not yet quantified and should be further reviewed in depth, if considered.” [23]

Brake’s position

1 Real world crash investigation
• Fund and deliver a pan-European collision investigation programme that prioritises, among other things, investigating VRU collisions with cars.
2 Mandate monitoring tests
The EC should retain its existing mandated tests (lower leg form to bumper, and head forms to bonnet) and:
• Mandate in the PPR the adult headform to windscreen protection monitoring test, with an impact speed of at least 40km/h
• Mandate the test of an upper leg form against a bonnet leading edge, in line with the latest EuroNCAP testing procedure.
3 Introduce more monitoring tests
• Introduce adult headform to A pillar monitoring tests at 40km/h
• Devise a test between vehicles with higher BLEs and a child’s head form and small adult thorax.
4 Publicise test results
• Ask type-approval authorities to collate and communicate every 3 years regarding all test results.


End Notes

[1] Reported Casualties Great Britain, June 2016
[2] Chart 2: Casualty and fatality rates per billion passenger miles by road user type: GB, 2014, Reported Casualties Great Britain, June 2016
[3] Dietmar, O., Birgitt, W. (2012) Comparison of Injury Situation of Pedestrians and Bicyclists in Car Frontal Impacts and Assessment of Influence Parameter on Throw Distance and Injury Severity.
[4] R Cookson, R Cuerden, D Richards, J Manning, TRL, A review of the causes of fatal pedestrians’ injuries resulting from collisions with car fronts – comparing vehicles registered in 2002 or later with earlier models, IRCOBI Conference 2009
[5] TRL, Study 26
[6] R Cookson, R Cuerden, D Richards, J Manning, TRL, A review of the causes of fatal pedestrians’ injuries resulting from collisions with car fronts – comparing vehicles registered in 2002 or later with earlier models, IRCOBI Conference 2009
[7] TRL, Study 26
[8] ACEA, 2015
[9] NASS-CDS
[10] Richard Cuerden, Mervyn Edwards, Matthias Seidl, TRL for European Parliament, Research for tran committee - the impact of higher or lower weight and volume of cars on road safety, particularly for vulnerable users, 2015
[11] Pedestrian Protection Regulation (78/2009)
[12] 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, 2015
[13] ibid
[14] ibid
[15] ibid
[16] EC, Saving lives: Boosting car safety in the EU, 2016
[17] EC, Saving lives: Boosting car safety in the EU, 2016
[18] 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, 2015
[19] Dietmar, O., Birgitt, W. (2012) Comparison of Injury Situation of Pedestrians and Bicyclists in Car Frontal Impacts and Assessment of Influence Parameter on Throw Distance and Injury Severity
[20] 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, 2015
[21] Dietmar, O., Birgitt, W. (2012) Comparison of Injury Situation of Pedestrians and Bicyclists in Car Frontal Impacts and Assessment of Influence Parameter on Throw Distance and Injury Severity
[22] Euro NCAP Pedestrian Testing Protocol December 2016
[23] 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

Page uploaded: March 2017