There has been limited investigation regarding occupant safety in transit bus crash scenarios. Experimental testing and numerical modelling can provide the insight required to reduce injury risk to transit bus passengers. Transport Canada (TC) has conducted a series of full-scale bus crash and frontal impact deceleration sled experiments as part of a research program to inform the development of crashworthiness standards for transit buses. Anthropomorphic Test Devices (ATD) were used in the TC experiments to assess occupant injury. ATDs have known limitations in replicating the response of a human passenger, primarily due to an overly stiff neck and thorax. Finite element ATDs and Human Body Models (HBM) are biofidelic occupant surrogate models that can be used in numerical crash simulations to predict response and localized tissue injury. This study expanded on the TC experimental work by using numerical simulations to assess transit bus passenger response and injury risk using a contemporary detailed HBM in a frontal impact scenario.

A numerical model of the TC sled buck was developed and validated for a series of eight frontal impacts utilizing 50th and 5th percentile Hybrid III (HIII) ATD models as the occupants. The Global Human Body Models Consortium (GHBMC) male 50th percentile (M50) and female 5th percentile (F05) HBMs were seated in the test buck model and simulated for a 6.5g frontal impact pulse. The 50th percentile occupants impacted the forward handrail on the anterior side of the neck, which posed a risk of a crushing injury to the larynx cartilage. A crushing injury to the larynx could occlude airways and is a potentially fatal injury. The 5th percentile passenger showed a potential for impacting the forward handrail on the lower face instead of the anterior neck, resulting in a mandible and upper neck injury.

This study investigated passive safety designs that could minimize the potential for passenger injury on transit buses without implementing seat belts. A lowered handrail resulted in the passenger being impacted on the thorax instead of the neck, effectively eliminating the injuries of the larynx, mandible, and neck at the expense of increased chest compression. The chest compression of the small stature HBM predicted a sternum fracture, which was still preferable over the crushing larynx injury observed in the experimental test buck design.

This study demonstrated that the placement of rigid handrails could put passengers at risk of focal impact injuries during a crash. Simple design changes, such as lowering the handrail to engage the thorax instead of the face or neck, proved to be an effective way to avoid potentially lethal injury. Future work should investigate passenger injury using HBMs in other transit bus impact configurations, such as rear and side impacts with varying pulse severities.