Uploaded to Knowledge Centre
15 September 2021
The overall aim of the ‘RoaD’ project was to improve understanding of pedestrian injuries incurred as a result of a collision with a vehicle. In particular, the project set out to understand whether it is possible to create a pedestrian trauma database containing vehicle profiles, and capable of predicting the likely injury severity based on the impact speed, and depending on the vehicle involved and pedestrian stature.
In order to create a pedestrian trauma database the project looked to determine whether it is possible to develop a model and calculate trauma at organ level in pedestrian collisions.
The project concluded that a pedestrian trauma database (PTD) could be created, resulting in the improvement of blood loss modelling in human body computer models (HBM). However, further work is required to investigate whether it is possible to model levels of fluid inside the HBM, as well as haemorrhage.
The project led to the funding of two joint PhDs between the University Hospital of Coventry and Warwickshire and West Midlands Ambulance Services, which should bridge the gaps to the generation of the PTD.
The project was endorsed and supported by UK Police Force (UKPF), UK Coroners, EuroNCAP and the charity RoadPeace.
More accurate and timely understanding of pedestrian injury severity has a number of potential benefits including improved A&E responses, a less distressing Coronial process for families, and new techniques to support law enforcement applications.
The project methodology required a large dataset of pedestrian fatalities, provided by UKPF, from which vital organ injury severities could be extracted. These collisions were reconstructed using computer modelling to ultimately generate a calibrated injury model, which was then used to populate the PTD.
As ageing is an important parameter (because people become increasingly frail with age), it was necessary to access a large number of collision data samples to cover the widest range of ages, allowing the PTD to capture the trauma severity across the entire population.
At the outset of the project, scientific literature revealed that a Maximum Principal Strain (MPS) reading – a current standard method used in the scientific community to extract injury in computer models – was not adequate to extract all levels of injury severity.
Fortunately, a concept known as Peak Virtual Power (PVP), derived in 2001 by Prof Clive Neal-Sturgess, had the potential to solve this deficiency, and was selected for this project. This method uses the 2nd Law of Thermodynamics, stating that after an impact Entropy (a measure of the molecular disorder) increases – hence suggesting organ degeneration and damage. This disorder is computed by extracting the maximum power experienced by each organ during the collision, and linking it to the threat to life using the Ordinal abbreviated injury scale (AIS), which ranges from 1 (minor) to 5 (critical).
This method had never been applied to human body computer models (HBM) and had never been used to capture differences in trauma severities as a function of ageing.
Unfortunately, due to an unexpected reduction in the number of UKPF support staff, it was not possible to approach the study as originally planned, which was through access to collision data as incidents occurred.
Instead, a mathematical approach was undertaken which led to the derivation of an innovative and unique Organ Trauma Model (OTM). The OTM linked the impact energy (kinetic energy), deformation energy (strain energy) and the concept of power, which is represented by the product of pressure (stress) on the organ and its rate of deformation (strain rate).
As the organ deformation for a given load is material dependant, it was possible to include the ageing material degradation, as well as the organ volume variation as a function of ageing, making the OTM a universal trauma model, able to capture trauma across the entire population.
The OTM was tested against three pedestrian collisions provided by UKPF and used the Total Human Model for Safety (THUMS) for trauma severity extraction, which had been adjusted to represent the height and weight of the deceased. Due to time constraints, the study only focused on brain white and grey matter injuries.
The results confirmed that the OTM projected accurate trauma brain injury severities when bleeding did not occur, and under-predicted when bleeding was observed by the pathologist. The differences observed were an inherent limitation of the computation method which kept the volume of the organ constant.
Conveniently, this computation limitation also confirmed that the OTM was physically representative to real world trauma responses, as OTM stipulates that injury severity is inversely proportional to the organ volume, i.e. a volume loss leads to a greater trauma.
The results confirmed that the OTM trauma severity predictions were more accurate than the standard MPS method currently used by the scientific community, as MPS results were consistently over-predicting injury outcomes. Furthermore, the OTM model had the capability to rate the injury severity level occurring under the critical trauma severity level, which is a breakthrough in its own right.
This finding has been reported to JSOL, reseller of THUMS, which are in the process of including the OTM trauma model as part of their brain trauma indicators, which will be accessible by the scientific community worldwide.
The project concluded that a PTD could be created, resulting in the improvement of blood loss modelling in HBM. However, further work is required to investigate whether it is possible to model levels of fluid inside the HBM, as well as haemorrhage.
The project team also gained a better understanding of the parameters influencing the trauma outcome of pedestrian collisions, and consequently believes that the PTD could also be approached using data mining and machine learning techniques.
This finding led to the funding of two joint PhDs between the University Hospital of Coventry and Warwickshire and West Midlands Ambulance Services to investigate these new challenges. These two new research projects, generated from the RoaD grant award, should bridge the gaps to the generation of the PTD.
For more information and to access the full project report, visit the Road Safety Trust website: