Original publication: November 2015
Authors: TRL Limited, United Kingdom: Richard Cuerden, Mervyn Edwards, Matthias Seidl
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The Impact of Higher or Lower Weight and Volume of Cars on Road Safety, Particularly for Vulnerable Users

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The road environment, road users and the make-up of the vehicle fleet are changing in the European Union. Current societal trends, such as an increase in the number of pedestrians and cyclists driven by environmental or green policies, an increase in the proportion of SUVs in the vehicle fleet and an ageing society are all factors that will directly affect tomorrow’s road safety problem.

In the last 10 years the European Union has seen significant reductions in the number of people killed in road traffic accidents, but the number of Vulnerable Road Users (VRU) has become an increasingly important proportion of the total casualty figures, in part due to the successes associated with preventing car user injury.

The objective of this study is to provide the Members of the Committee on Transport and Tourism of the European Parliament with an in-depth analysis of necessary technological changes, in order to improve the impact of higher or lower weight and volume of cars on road safety, particularly for, but not limited to vulnerable users.


The study considered whether SUVs and MPVs are more aggressive than smaller passenger cars in collisions with VRUs and whether there are disadvantages to being in a small (light) car in an accident with a bigger (heavier) car, e.g. a SUV.

No real world accident data evidence was found showing that modern European SUVs or MPVs are more aggressive towards VRUs than smaller passenger cars. This is in stark contrast with international findings, which show a higher VRU injury risk for these vehicles. This might be explained by more pedestrian-friendly vehicle design, based on European regulatory requirements, or more likely simply by an insufficient European evidence base and research to be able to identify this trend. It should be noted that the kinematics are different for pedestrians struck by SUVs compared to passenger cars because of the higher bonnet leading edge. This causes a more severe impact to the pedestrian’s femur and pelvis area with less upper body and head rotation leading to different injury patterns, in which some injuries can be more severe.

Further pan-European research is therefore warranted to address the question whether it is necessary to improve the pedestrian protection legislation for larger vehicles, or indeed all passenger vehicles.

As regards the question of whether there are disadvantages to being in a small (light) car in an accident with a bigger (heavier) car, e.g. a SUV, the study concluded that the risk of injury is typically greater in the smaller car if all other things are equal. However, all other things are rarely equal and vehicle design is an important factor, for example how well stiff structures in the two vehicles are aligned (structural interaction) and the presence of safety equipment and interior padding. UK accident data showed that, for all accident types, the injury rate for occupants in smaller cars was higher than that in SUV and MPV type vehicles. In contrast, US accident data showed that a person has no greater fatality risk driving an average car compared to a much heavier truck based SUV. This discrepancy between the regions is likely to be associated with different collision typologies and fleet characteristics, with proportionally many more SUVs, MPVs and pick-up vehicles in the US.

The study discusses potential measures to address these issues and the effect of an aging population. Not all possible measures were considered, because the focus was on those that are technically feasible, likely to be affordable and that will give greatest benefit with respect to a regulatory cost benefit study. For example, there are two fundamental approaches to resolving the problem that you will be at a disadvantage if you are in a small (light) vehicle, which collides with a bigger (heavier) vehicle, e.g. an SUV, assuming all other things are equal. The first is to make the vehicle sizes and weights more even and the second is to improve protection, in particular for the occupants of the small (light) vehicle. In this study the emphasis was placed on the second approach because the authors believe that this is the most realistic and therefore offers a greater chance of success, because it can help address other issues as well, such as the lower bio-mechanical tolerance of older people who are becoming a larger proportion of the population.


Improved accident data collection
First and fore most it is essential that the best road casualty data practicable is collected in a harmonised way across Europe. Currently, it is not possible to fully answer the questions raised in this review, because of the lack of real world evidence. A pan European accident investigation programme, similar to the NASS-CDS work in the US, would afford the European Parliament and the citizens of the Union a clear and quantifiable measure of current problems. Perhaps, more importantly such data would inform the development of applicable and cost effective policies, technologies and solutions to prevent future loss of life and injury on our roads. To maximise the potential, such in-depth accident sampling data should be made freely available to help democratise safety and remove commercial barriers to saving lives.

Measures to improve safety of VRUs

  • Fitment of Advanced Driver Assistance Systems (ADAS), which help the driver with the driving process, should be considered, in particular: Pedestrian and cyclist capable Autonomous Emergency Braking systems (AEB); Intelligent Speed Assistance systems (ISA); Lane Keeping Assist (LKA); Reversing cameras.
  • Improvement to crashworthiness of the vehicle structure should be considered, in particular: Improved A-pillar and windscreen frame protection; Improved bonnet leading edge design for upper leg, pelvis and thorax protection.

Measures to improve safety of vehicle occupants

Fitment of the following should be considered:

  • Adaptive restraint systems for frontal impacts.
  • Curtain airbags for side impacts.
  • More stringent crash test legislation for car-like heavy on-road quadricycles.

Also measures to improve crash compatibility should be considered further, in particular those to improve structural interaction of SUVs in frontal impacts.

Link to the full study: http://bit.ly/563-415

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