Title:
Motorcycle helmets: head and neck dynamics in helmeted and unhelmeted oblique impacts.

Abstract:
To assess the factors that contribute to head and neck dynamics in motorcycle crash simulation tests.
A series of laboratory tests was undertaken using an oblique impact rig. The impact rig included a drop assembly with a Hybrid III head and neck. The head struck the top surface of a horizontally moving striker plate. Head linear and angular acceleration, striker plate force, and upper neck loads were measured. The following test parameters were varied: drop height to a maximum of 1.5 m, horizontal speed to a maximum of 35 km/h, impact orientation/location, and restraint adjustment. Two helmet models were used for the majority of tests. Visor impacts were conducted as were comparisons across 4 helmet models. Descriptive statistics were derived and multiple regression was applied to examine the role of each parameter. The data were compared to unhelmeted tests.
The tests confirmed that motorcycle helmets compared to no helmet provide a high level of protection to the head and neck through management of both linear and angular head acceleration and neck loads. In the most severe lateral impacts (drop height 1.5 m and horizontal speed 35 km/h): the mean head injury criterion (HIC₁₅) and mean maximum headform acceleration were respectively 648, 150 g for 4 helmet models; the mean +αy was +9.5 krad/s² and +αx was +5.1 krad/s²; the upper neck resultant force, -Mx and -My, respectively, were 4947 N, -80 Nm, and 55 Nm. Drop height was a significant predictor of peak linear headform acceleration, HIC₁₅, and striker force. Horizontal speed and impact orientation were significant predictors of peak angular acceleration, in addition to drop height. Peak head and neck loads observed in visor impacts were similar to those observed in impacts directly to the shell. Peak head and neck loads observed in frontal impacts with tightly and loosely adjusted restraints were similar, but the helmet with the loosely adjusted restraint was ejected during the impact.
Further research and development is required on the oblique test rig to establish its reliability and validity, the latter through comparisons to real-world impacts. Motorcycle helmets certified to a national standard manage linear acceleration well, but further developments are required to reduce angular acceleration. Within the range of impact conditions, there was no indication that helmets posed a neck injury risk.