A rubberized impact absorbing pavement can reduce the head injury risk in vulnerable road users: A bicycle and a pedestrian accident case study.

OBJECTIVE: Vulnerable Road Users (VRU), including pedestrians and cyclists, are generally the least protected road users and are frequently missed in the planning process of preventive measures. Rubberized asphalt mixtures were originally developed as a possible environmentally friendly solution to recycle the End-of-Life Tires while making the pavements more durable. The objective of the current study was to explore the effects of increasing the rubber content of the common rubberized asphalt mixtures in reducing the head injuries risk for VRUs. METHOD: To achieve this purpose, four different sample series with 0, 14, 28, and 33 weight percent rubber in each were tested. A compressive test without permanent deformation and one with failure were performed on each sample series. The mechanical behavior of each set was modeled using a MAT_SIMPLIFIED_RUBBER material model in LS-Dyna and validated against a standard Head Injury Criterion (HIC) drop test. Ultimately, previously low-speed accident reconstructed cases, a bicycle and a pedestrian one, were used to assess the effect of varying the rubber content on reducing the head injury risk. RESULTS: In the bicycle accident case, the risk of skull fracture was reduced from 0.99 to 0.29 when comparing the non-rubberized asphalt mixture with the 33% rubber mixture. In the same accident case, the risk of concussion, evaluated using the logistic regression method, was reduced from 0.97 in the non-rubberized mixture to 0.81 in the 33% rubber mixture. The initial conditions, linear and rotational velocities, were lower for the pedestrian case compared to the bicycle case (the bicycle case was more severe compared to the pedestrian case), which led to lower strains in the pedestrian case. In the pedestrian accident case, the risk of skull fracture was reduced from 1.00 in the non-rubberized mixture to 0.63 in the 33% rubber mixture, while the risk of concussion was reduced from 0.64 to 0.07. CONCLUSION: The rubberized asphalt mixtures could reduce the head injury risk for the studied cases when the rubber content in the asphalt mixture increases.

Upright trunk and lateral or slight anterior rotation of the pelvis cause the highest proximal femur forces during sideways falls.

Whole-body models are historically developed for traffic injury prevention, and they are positioned accordingly in the standing or sitting configuration representing pedestrian or occupant postures. Those configurations are appropriate for vehicle accidents or pedestrian-vehicle accidents; however, they are uncommon body posture during a fall accident to the ground. This study aims to investigate the influence of trunk and pelvis angles on the proximal femur forces during sideways falls. For this purpose, a previously developed whole-body model was positioned into different fall configurations varying the trunk and pelvis angles. The trunk angle was varied in steps of 10° from 10 to 80°, and the pelvis rotation was changed every 5° from -20° (rotation toward posterior) to +20° (rotation toward anterior). The simulations were performed on a medium-size male (177 cm, 76 kg) and a small-size female (156 cm, 55 kg), representative for elderly men and women, respectively. The results demonstrated that the highest proximal femur force measured on the femoral head was reached when either male or female model had a 10-degree trunk angle and +10° anterior pelvis rotation.

Influence of nonlinear soft tissue modeling on the external and internal forces during lateral hip impacts.

Soft tissues in the hip region, which are typically considered the natural shock-absorbers during falls, attenuate the applied forces to the underlying hard tissue. The soft tissue thickness is, therefore, a significant parameter in the force attenuation. Another factor that could affect the assessment of the force attenuation in numerical simulations is the choice of constitutive model and material parameters for the soft tissue. Several constitutive models and parameters for muscle and adipose tissue were suggested in the published literature; however, the biofidelity of the proposed models for the lateral impacts has not been assessed yet. To achieve this purpose, we used a previously developed human body model named THUMS v4.02 and modified the mechanical properties and geometry of the soft tissues in the hip region. The simulations consisted of regional hip models and whole-body models. The biofidelity of the constitutive models of muscle and adipose tissue was determined objectively using the CORrelation and Analysis (CORA) rating. Moreover, the potential force attenuating effect of the adipose tissue thickness was investigated in the regional models. We collected and fitted several available nonlinear material models for muscle and adipose tissue and implemented them. The CORA ratings for several constitutive models for adipose tissue in the regional model were above 0.8. Among the muscle constitutive models, three Ogden models consistently rated above 0.58 for the whole-body model. Moreover, the impact forces in the selected adipose tissue model attenuated 47 N for every 1 mm increase in thickness. Overall, the choice of the nonlinear material model for the adipose and muscle tissue influences the external and internal force, and the difference between the material models is more pronounced when the thickness of the soft tissue increases.