Motorcycle Helmets: Head and Neck Dynamics in Helmeted and Unhelmeted Oblique Impacts

Abstract

Objective: To assess the factors that contribute to head and neck dynamics in motorcycle crash simulation tests.

Method: 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.

Results: 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.

Conclusions: 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.

Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Keywords:

• motorcycle helmet
• brain injury
• neck injury
• impact biomechanics
• test methods

Acknowledgments

This work was conducted at the Biomechanics and Gait Laboratory, School of Risk and Safety Sciences, UNSW, under funding by an Australian Research Council (ARC) Linkage Grant LP0669480 Pedal and Motor Cycle Helmet Performance Study. The project partners are the Commonwealth Department of Infrastructure and Transport, Roads and Maritime Services NSW, Transport Accident Commission Victoria, NRMA Motoring and Services, NRMA-ACT Road Safety Trust, and DVExperts International. The authors thank the Roads and Maritime Services Crashlab and its staff for their assistance. The authors thank Dr. George Rechnitzer, Ross Dal Nevo, Professor Raphael Grzebieta, and Dr. Toh Yen Pang for their involvement in the development of the oblique test rig. Edgar Schilter's assistance with conducting the oblique impact tests is greatly appreciated. Finally, a special acknowledgement goes to Bruce Dowdell of Roads and Maritime Services NSW for raising an awareness of these issues many years ago.