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Research Article Open Access
Lloyd, J Forensic Biomed 2017, 8:3
DOI: 10.4172/2090-2697.1000135
Research Article OMICS International
Journal of
Forensic Biomechanics
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ISSN: 2090-2697
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
Keywords: Biomechanics; Motorcycle accident; Motorcycle helmet;
Skull fracture; Concussion; Subdural hematoma; Brain injury
Introduction
In developing countries motorcycles are required for utilitarian
purposes due to lower prices and greater fuel economy, whereas in
the developed world they are considered a luxury and used mostly
for recreation. In 2016 there were more than 134 million motorcycles
worldwide, 8.4 million of which were registered in the United States,
representing 3.2% of all US registered vehicles. California, Florida and
Texas were the leading states in terms of the motorcycle popularity;
collectively representing 22% of all US registered motorcycles. In 2011,
U.S. motorcyclists travelled a total of 18.5 billion miles, which, while
only 0.6% of total vehicle miles travelled, accounted for 14.6% (4,612)
of U.S. trac fatalities that year. Worldwide there are more than 340,000
motorcyclist fatalities annually, which equates to more than 28%
of all road accident deaths. According to the U.S. National Highway
Trac Safety Administration [1] and other reports, when compared
per vehicle mile traveled with automobiles, due to their vulnerability,
motorcyclists' risk of a fatal crash is 30-35 times greater than that of a
car occupant.
Two fundamental epidemiologic studies into the causation of
motorcycle accidents have been conducted: the Hurt study in North
America and the MAIDS [2] study in Europe. According to the Hurt
Report, 75 percent of collisions were found to involve a motorcycle
and a passenger vehicle, while the remaining 25% were single vehicle
accidents. e cause of motorcycle versus passenger vehicle collisions
in 66% of accidents involves violation of the rider’s right of way due to
the failure of motorists to detect and recognize motorcycles in trac.
Findings further indicate that severity of injury to the rider increases
with alcohol consumption, motorcycle size and speed.
*Corresponding author: John D Lloyd, Assistant Professor, University of South
Florida, College of Engineering, Tampa, Florida 33576, Tel: 813-624-8986; E-mail:
DrJohnLloyd@Tampabay.RR.com
Received September 11, 2017; Accepted September 25, 2017; Published
October 02, 2017
Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets:
Protection against Head and Brain Injuries. J Forensic Biomed 8: 135. doi:
10.4172/2090-2697.1000135
Copyright: © 2017 Lloyd JD. This is an open-access article distributed under the
terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Abstract
Motorcycle accident victims worldwide account for more than 340,000 fatalities annually, with the Unites States
ranking 8th highest in number of motorcycle accident deaths, largely due to non-mandatory motorcycle helmet
requirements for adults in a number of States. Seventy-ve percent of all fatal motorcycle accidents involve head and
brain injury, with rotational forces acting on the brain the primary cause of mortality. Current motorcycle helmets are
reasonably effective at reducing head injuries associated with blunt impact. However, the mechanism of traumatic
brain injury is biomechanically very different from that associated with focal head injury. This study was conducted to
evaluate the effectiveness of current motorcycle helmets at reducing the risk of traumatic brain injuries.
Ten motorcycle helmet designs, including full-face, three-quarter and half-helmets were evaluated at an average
impact velocity of 8.3 ms-1 (18.5 mph) using a validated test apparatus outtted with a crash test dummy head and
neck. Sensors at the center of mass of the headform enabled high-speed data acquisition of linear and angular head
kinematics associated with impact.
Results indicate that none of the standard helmet models tested provides adequate protection against concussion
and severe traumatic brain injuries at moderate impact speeds. Only one of the standard motorcycle helmet models
tested provided adequate protection against skull fracture.
A new motorcycle helmet prototype, incorporating a liner constructed from a composite matrix of rate-dependent
materials was tested, with comparison to standard motorcycle helmet designs, with very promising results. Knowledge
learned from this study will facilitate the development of a new generation of advanced motorcycle helmets that offer
improved protection against both head and brain injuries.
Biomechanical Evaluation of Motorcycle Helmets: Protection against Head
and Brain Injuries
John D Lloyd*
University of South Florida, College of Engineering, Tampa, Florida
e most recent epidemiologic study to investigate motorcycle
accident exposure data was conducted between 1999-2001 by a
partnership of ve European countries. Findings show that passenger
cars were again the most frequent collision partner (60%), where more
than two-thirds of drivers reported that they did not see the motorcycle
and more than half of all accidents involving motorcycles occurred at
an intersection.
e COST report, which is an extension of the MAIDS [2] study,
documents that three-quarters (75%) of all motorcyclist deaths are a
result of injury to the head and brain. Linear forces were the major
factor in 31% of fatal head injuries, while rotational forces were found
to be the primary cause in over 60% of cases.
While the helmet is considered the most eective means of rider
protection, recent studies indicate that motorcycle helmets are only 37-
42% successful in preventing fatal injury. By reducing peak linear forces
acting on the head it was commonly believed that the risk of diuse
brain injuries, including concussion, subdural hematoma and diuse
Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets: Protection against Head and Brain Injuries. J Forensic Biomed 8: 135.
doi: 10.4172/2090-2697.1000135
Page 2 of 6
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
axonal injury would also be prevented [3]. However, the biomechanical
mechanisms of head and brain injuries are unique. New research shows
that these mechanisms are poorly correlated.
Motorcycle Helmet Standards
Like most helmets, motorcycle helmets are modeled aer ancient
military helmets, the purpose of which is to provide protection against
penetrating head injury, such as skull fracture. Whereas, all impacts
have both linear and oblique components which produce translational
and tangential forces, respectively. e modern motorcycle helmet was
introduced over 60 years ago. Its outer shell serves as a second skull,
diusing impact forces over a larger surface area, while the inner liner
compresses to minimize translational forces. However, a mechanism
to mitigate tangential forces is absent. Since the liner lls the entire
inner surface of the shell and is immobile, rotational inertia induced
tangential forces are transmitted directly to the brain.
e likelihood of a helmeted motorcyclist sustaining impact loading
injuries, such as skull fractures, can be determined by quantifying the
magnitude of peak linear acceleration experienced by a test headform
in response to impact. Whereas the risk of a rider suering inertial
or impulse loading injuries, such as concussion, axonal injury and
intracranial hematoma can be computed based on impact-related
angular kinematics at the headform center of mass.
Unfortunately motorcycle helmet protection is not driven, for the
most part, by advances in scientic knowledge, but by the need to
meet applicable testing standards. In the United States, the governing
specication is the federal motor vehicle safety standard (FMVSS)
#218; the Snell Memorial Foundation also oers a voluntary standard
M2015, which is a little more stringent. Whereas BSI 6658 and ECE
22.05 have been adopted in European countries and AS/NZS 1698
accepted in Australasian countries [4-7]. Test protocols involve the
guided fall of a helmeted headform onto steel anvils of various designs
at impact velocities ranging from only 5.2 to 7.5 m/s (11-17 mph). e
pass/fail criterion is based only on the helmet’s eectiveness in reducing
peak linear acceleration, and thereby translational forces, in response
to impact.
Impact-related angular head kinematics are not quantied under
current motorcycle helmet standards, which therefore fail to assess
whether helmets oer any protection against traumatic brain injuries.
e omission of this critical measure of helmet performance is reected
epidemiologically in the disproportion of closed head and brain injuries
in fatal motorcycle accidents [2,8].
Biomechanics of Head and Brain Injury
e two mechanisms associated with traumatic head and brain
injury are impact loading and impulse loading, both of which are
present in all impact events. Impact loading involves a blow directed
through the center of mass of the head, resulting in translation of the
head and brain. When thresholds of injury are exceeded, skull fractures,
lacerations and contusions (bruising) to the head and underlying brain
tissue may result. Whereas, impulse or inertial loading is produced
when an oblique impact, common to motorcycle crashes, creates
tangential forces, causing head rotation. Since the brain is not rigidly
attached to the inside of the skull, rotational inertia of the brain
produces a mechanical strain on cerebral blood vessels, nerve bers and
brain tissue. When thresholds of injury are exceeded, nerve bers in the
brain may be damaged, producing concussion and diuse axonal injury
(DAI). Blood vessels may also rupture, causing subdural hemorrhages
(SDH), the high mortality rate of which has motivated numerous
studies of bridging vein failure properties. Subdural hematoma and
traumatic axonal injury are frequently identied as the cause of serious
injury or fatality in motorcycle accidents.
Holbourn [9] was the rst to identify angular / rotational
acceleration as the principal mechanism in brain injury. Gennarelli
et al. [10] further investigated the importance of rotational (angular)
acceleration in brain injury causation, based on studies involving
live primates and physical models, [11,12], concluding that angular
acceleration is far more critical than linear acceleration to the causality
of traumatic brain injuries. ey further isolated and investigated the
unique eects of translational (linear) and inertial (angular) loading on
the heads of primates [11], conrming that pure translation produces
focal injuries, such as contusions and skull fractures, while rotationally
induced inertial loading causes diuse eects, including concussion
and subdural hematoma. Closed head and brain injury, found in more
than 60% of motorcycle accident fatalities, is due to inadequate helmet
protection against impact-related angular head kinematics [8].
Skull fracture
Ono [13] published thresholds for human skull fracture based on
cadaver experiments. Twenty-ve human cadaver skulls were exposed
to frontal, occipital and lateral impacts. Each skull was covered with
the rubber skin of a Hybrid II mannequin and lled with gelatin to
accurately represent head mass. A series of 42 frontal, 36 occipital
and 58 temporal blows were delivered to the suspended heads, during
which linear accelerations were measured. A skull fracture threshold
of 250 g for 3-millisecond impulse duration was established for frontal
and occipital impacts, decreasing to 140 g for 7-millisecond impulse
duration. Whereas the skull fracture threshold for lateral impacts is
reported as 120 g over 3-millisecond duration, decreasing to 90 g over
7 milliseconds. Results indicate that skull fracture threshold is inversely
related to impulse duration.
Concussion
Several studies have attempted to establish biomechanical
thresholds for concussion. Pellman et al. [14] analyzed a series of
video-recorded concussive impacts during NFL football games,
reporting that concussive injury is possible at 45 g/3500 rad/s2, while
5500 rad/s2 represents a 50% risk of concussive trauma. Rowson
and Duma [15], also using head injuries in America football as their
model, conducted extensive laboratory and eld-based biomechanical
evaluations, Based on data from 62,974 sub-concussive impacts and
37 diagnosed concussions recorded using the Simbex, Inc. (Lebanon,
NH) Head Impact Telemetry System (HITS), the investigators propose
a concussion threshold of 104 ± 30 g and 4726 ± 1931 rad/s2.
Subdural hematoma
According to Gennarelli [12], the most common form of acute
subdural hematoma (ASDH) is caused by shearing of veins that bridge
the subdural space [12]. e severity of injury associated with bridging
vein rupture has led to numerous studies of their mechanical properties
Lowenhielm et al. [16-21].
Lowenhielm tested 22 human parasagittal bridging vein samples
from 11 decedents between the ages of 13 and 87 years without history
of brain injury [16,17]. He hypothesized that blunt trauma to the head
causes the brain to be displaced with respect to the dura, thereby
stretching bridging veins and surrounding connective tissue. Based on
his laboratory experiments, Lowenhielm[16,17] found that maximal
Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets: Protection against Head and Brain Injuries. J Forensic Biomed 8: 135.
doi: 10.4172/2090-2697.1000135
Page 3 of 6
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
shear stresses occur about 7 milliseconds aer impact, coinciding with
bridging vein disruption. He concluded that bridging vein rupture may
occur if peak angular acceleration exceeds 4500 rad/s2.
Depreitere [21] subjected ten unembalmed human cadavers to
18 occipital impacts producing head rotation of varying magnitude
and impulse duration in the sagittal plane 35. Bridging vein ruptures,
detected by autopsy, were produced in six impact tests. Findings suggest
a mean tolerance level of approximately 6,000 rad/s2 for 10-millisecond
impulse duration, which seems to decrease for longer impulse durations;
however the condence interval is rather broad due to the limited data
set. Data from the research by Depreitere [21] and Lowenhielm [16,17]
is presented in Figure 1.
Helmets decrease peak translational force by extending the impulse
duration. In the case of motorcycle helmets, typical impulse duration
is approximately 12 milliseconds. Figure 1 suggests that bridging vein
rupture may result with peak angular accelerations in the order of 5,000
rad/s2, but may be as low as 3,000 rad/s2 aer adjusting for standard
error of the mean in this limited dataset.
While previous studies have investigated motorcycle impacts into
vehicles and xed barriers, the underlying motivation of such studies
was to determine crush characteristics of the vehicles for accident
reconstruction purposes. Other studies have evaluated peak linear
accelerations of the head, chest and pelvis of motorcyclists in collisions.
However, rotational forces associated with impact-related peak angular
accelerations have not been determined even though it is well known
that rotational mechanisms are the primary cause of closed head
injuries [9-12,22] in helmeted motorcyclist accidents [8]. Measurement
of impact-related head angular/rotational acceleration is critical to the
development and evaluation of motorcycle helmets to provide eective
protection against traumatic brain injuries associated with a range of
typical motorcycle crash-related head impact speeds. To that end, this
paper oers an objective determination of the performance of a variety
of motorcycle helmets in terms of their ability to protect against both
head and traumatic brain injuries associated with impact velocities
reective of typical head impact velocities in motorcycle accidents.
Methods
e standard test apparatus for impact testing of protective
headwear was modied to enable measurement of both linear and
angular headform kinematics [23]. is validated apparatus is
comprised of parallel vertical braided stainless steel wires that guide
the fall of a 50th percentile Hybrid III head and neck assembly
(Humanetics ATD, Plymouth, MI) mounted to an aluminum yarm.
e anvil onto which the headform impacts consists of a 50 mm thick
steel base plate, with a 100 mm thick concrete overlay, consistent with
the coecient of friction for typical roadway surfaces (Figure 2).
According to Mellor et al. [24] apparatus for the evaluation of
protective headgear in which the headform is rigidly axed to the
carriage (yarm) reduces the dissipation of energy by excessive rotation
of the helmeted headform and sliding of the helmet on the anvil,
thereby inating peak linear acceleration measures. Examples in which
the headform is rigidly axed to the yarm include the FMVSS218 test
apparatus 20. Whereas in Snell M2015 21, BS 6658 22 and AS/NZS 1698
24 [4,5,7] specications the headform is attached to the yarm by means
of a hinge joint, which allows headform rotation in the sagittal plane as
well as vertical translation, but prevents motion in the coronal and axial
planes. e ECE 22:05 [6] test method 23 utilizes a ball joint between
the yarm and headform, thereby permitting unrestricted head rotation
Figure 1: Bridging vein failure as a function of impulse duration and peak
angular acceleration (with line of best t and 75% condence intervals).
Figure 2: Modied head drop system with Hybrid III head/neck.
in all three planes. Similar to the ECE test method, utilization of the
Hybrid III neck permits headform rotation in sagittal, coronal and
axial planes, but limits the rate of motion in a manner more consistent
with the human musculoskeletal system. Moreover, orientation of the
Hybrid III neck was maintained relative to the yarm, irrespective of
headform orientation, thereby standardizing response of the neck form.
Instrumentation: A triaxial block, installed at the center of mass of
the Hybrid III headform (HumaneticsATD, Plymouth, MI) housed a
triaxial accelerometer from PCB Piezotronics (Depew, NY) and three
DTS-ARS Pro angular rate sensors (Diversied Technical Systems, Seal
Beach, CA). Data from the sensors were acquired using compact DAQ
hardware from National Instruments (Austin, TX).
While all sensors had been calibrated by the respective
manufacturers, verication tests were performed to validate linear
and angular sensor calibration data. Calibration of the tri-axial linear
accelerometer was validated using a portable handheld shaker and
found to be within specication for all three axes of measurement.
For the angular rate sensor a simple validation method was devised in
which the sensor was axed to a digital goniometer, which was moved
through a set angle (Figure 3). Using LabView, the integral of angular
rate was computed, reecting concurrence with the digital goniometer
for all three planes of motion.
Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets: Protection against Head and Brain Injuries. J Forensic Biomed 8: 135.
doi: 10.4172/2090-2697.1000135
Page 4 of 6
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
Figure 3: Validation of angular rate sensor calibration.
Ten motorcycle helmet models were selected for evaluation, based
on popularity among motorcyclists, including representative models of
full-coverage, three-quarter and half-helmet (shorty) styles, as shown in
Figure 4. All models displayed the DOT certication sticker, indicating
that their protective performance met the FMVSS218 motorcycle
helmet testing standard 20. Helmet sizes were chosen based on best t
for the Hybrid III headform, which has a 58cm head circumference,
representative of a 50th percentile US adult male.
In addition, a new prototype motorcycle helmet (Figure 5) was
tested for comparison against the ten standard DOT motorcycle
helmets. e prototype helmet was a three-quarter standard shell
with liner constructed from a composite of rate-dependent materials
arranged in a patent-pending matrix.
Five samples of each motorcycle helmet model were purchased in
new condition. Each helmet was impacted one time in the frontal and/
or occipital region at an impact velocity of approximately 8.3 meters per
second (18.5 mph), which was veried computationally. Repeatability
of the tests was conrmed at the start and end of data collection by
dropping the Hybrid III headform from a height of 2.0 m onto a
Modular Elastomer Programmer (MEP) pad of 25 mm thickness and
durometer 60A. Standard Error of the Mean of 0.061 was computed
based on peak angular accelerations for pre and post MEP pad drop
tests.
Analysis
Analog sensor data were acquired at 20 kHz per channel, in
accordance with SAE J211 [25], using LabView (National Instruments,
Austin, TX). e raw data was then ltered in MATLAB (e
MathWorks, Natick, MA) using a phaseless eighth-order Butterworth
lter with cuto frequencies of 1650 Hz and 300 Hz for the linear
accelerometers and angular rate sensors, respectively. Angular
acceleration measures were computed from the angular velocity data
using 5-point least-squares quartic equations. Impulse duration was
determined based on the linear acceleration signal, where impulse start
point is the time at which the magnitude of linear acceleration exceeds
3 g and impulse end point is the time at which the major component
of linear acceleration crosses the y-axis (Figure 6). e gradient from
impulse start point to peak was computed, as was the area under the
acceleration magnitude curve from start to end points. Variables for the
angular acceleration signal were similarly computed.
An analysis method validated by Takhounts [26] establishes physical
(strain and stress based) injury criteria for various types of brain injury
based on scaled animal injury data and uses Anthropomorphic Test
Bell Qualifier
Scorpion T510
Schuberth C1
Torc T-14
Shoei RJ-Platinum
Bell shorty
HJC shorty
Fuel HH series
VCan V531
Daytona skullcap
Bell shorty
HJC shorty
Fuel HH series
VCan V531
Daytona skullcap
Figure 4: Motorcycle helmet models evaluated.
Figure 5: Motorcycle helmet prototype.
Figure 6: Impulse duration based on linear acceleration data.
Device (ATD) test data to establish a kinematically based brain injury
criterion (BrIC) for use with ATD impact testing. is method was
utilized to express risk of brain injury according to the recently revised
AIS scale in terms of peak angular head kinematics, where:
( ) ( )
( )
2
22
/ 66.25 / 56.45 / 42.87= ++
coronal axial sagittal
BrIC AngVel AngVel AngVel
e probability of brain injury for AIS 1-5 was thus computed as a
function of BrIC:
Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets: Protection against Head and Brain Injuries. J Forensic Biomed 8: 135.
doi: 10.4172/2090-2697.1000135
Page 5 of 6
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
( )
2.84
1
−
= −
BrIC
n
P AIS e
Where, the value for n is substituted according to the table alongside:
AIS 1: 0.120 Mild concussion
AIS 2: 0.602 Severe concussion / post-concussion syndrome
AIS 3: 0.987 Moderate brain injury
AIS 4: 1.204 Severe brain injury
AIS 5: 1.252 Critical brain injury
Additionally, mechanical head and brain injury parameters of
maximum pressure (in kPa), maximum principal strain (MPS) and
cumulative strain damage measure (CDSM) were computed for each
helmet impact test:
Max pressure=peak linear acceleration magnitude × 0.9
MPS= -peak angular velocity magnitude × 0.01
CSDM= -(peak angular velocity magnitude × 0.01)-0.30
Results
A summary of results for each of helmet models evaluated in Table
1.
Motorcycle helmet protection against skull fracture
Figure 7 presents peak linear acceleration values, averaged across
5 samples of each of the 10 motorcycle helmet models tested, along
with results for the prototype, against pass/fail thresholds for current
motorcycle helmet testing standards (DOT, Snell, BS and ECE) [4-6,27]
as well as frontal-occipital and lateral skull fracture thresholds, per Ono
25.
Results show that while all of the motorcycle helmet models
evaluated satisfy at least the DOT [27] standard, only the Scorpion T510
full-face helmet oers sucient protection against fronto-occipital and
lateral impacts at the moderate impact velocities at which the helmets
were tested.
Motorcycle helmet protection against concussion
Figure 8 presents peak angular acceleration results for 8.3 m/s
impacts onto a concrete anvil, averaged across 5 samples of each helmet
model. e red horizontal line on Figure 8 indicates the 50% threshold
for concussive trauma, as dened by Pellman et al. [14].
Results show that while a DOT [27] approved motorcycle helmet
may reduce peak angular acceleration associated with a helmeted head
impact, the level of protection is not sucient to prevent concussive
injury in a typical motorcycle accident. Only the prototype motorcycle
helmet, incorporating a liner constructed from a composite of rate-
dependent materials arranged in a patent-pending matrix, oered
adequate protection against concussive events.
Motorcycle helmet protection against subdural hematoma
Figure 9 presents peak angular acceleration as a function of impulse
duration, averaged across 5 samples of each of the 10 motorcycle
helmet models tested, along with results for the prototype helmet. e
threshold for bridging vein failure and resultant subdural hematoma
is represented by the black line of best t. Upper and lower boundary
limits of this threshold are indicated in red, which represents a 75%
likelihood that a subdural hematoma may occur for peak angular
accelerations above the lower red line.
Most of the helmets tested, with exception of the prototype, fall
above the lower threshold line suggesting the likelihood of catastrophic
brain injury associated with a moderate helmeted impact. In fact, all
but one of the ve half-helmet models tested produced results above the
mean threshold for subdural hematoma, indicating a higher likelihood
of severe (AIS 4) or critical (AIS 5) brain injury. Overall, it appears that
full-face helmets generally outperform half helmets in reducing the risk
of subdural hematoma. Interestingly, an unhelmeted individual can
seemingly withstand substantially greater peak angular accelerations
and consequently experiences a lower risk of catastrophic brain trauma
than a helmeted individual.
Correlation analyses
Pearson’s correlations were computed between each of the variables.
Trends were suggested if computed R2 values were greater than 0.70,
while strong correlations are indicated if R2 exceeded 0.80. Across
all measures, the three most important variables, in rank order, for
determining risk of head and brain injury are peak angular acceleration,
angular acceleration gradient, and area under the angular acceleration
curve between impulse start to end. e following interesting results
were observed:
••A negative trend exists between helmet mass and both linear
acceleration (-0.70) and angular acceleration (-0.72). at is,
both peak linear acceleration and peak angular acceleration seem
to decrease as helmet mass increases.
••ere is neither a trend nor strong correlation between linear
velocity and any of the variables investigated. is nding
suggests that risk of head and brain injury is not related to impact
speed.
••A strong negative correlation exists between peak linear
acceleration and impulse duration (-0.92). at is, impulse
duration increases as peak linear acceleration decreases.
••A trend, but not strong correlation was found between peak
linear acceleration and peak angular acceleration, indicating
that reducing impact-related peak linear acceleration may not
necessarily mitigate peak angular acceleration.
••Peak angular acceleration is strongly correlated with rotational
injury criterion (RIC36) (0.95), Brain rotational Injury Criterion
(BrIC) (0.93), probability of brain injury AIS 2 through 5
(μ=0.91), angular acceleration gradient (0.98), and area under the
angular acceleration curve (0.96). A strong negative correlation
is identied between peak angular acceleration and cumulative
strain damage measure (CSDM) (-0.94) and maximum principal
strain (MPS) (-0.94). A positive trend is also noted between
peak angular acceleration and maximum pressure (0.77), Gadd
Severity Index (GSI) (0.74) and linear acceleration gradient
(0.76).
Discussion
As presented, the mechanisms associated with causation of focal
head injuries and diuse brain injuries are very dierent. Helmets
were originally intended and continue to be designed to reduce the
risk of potentially fatal head injuries caused by skull fracture fragments
Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets: Protection against Head and Brain Injuries. J Forensic Biomed 8: 135.
doi: 10.4172/2090-2697.1000135
Page 6 of 6
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
Mass
(grams)
Linear
Velocity
(m/s)
Linear
Accel
(g)
Angular
Velocity
(rad/s)
Angular
Accel
(rad/s2)
Max
Pressure
(kPa)
CSDM MPS BrIC
Probability of Brain Injury (%) Impulse
Duration
(msec)
AIS 1 AIS 2 AIS 3 AIS 4 AIS 5
Unhelmeted n/a 9.5 1020.0 48.7 25009 918.0 -0.79 -0.49 0.97 100 73.2 53.3 42.7 40.5 2.00
Bell Qualier 1484 9.2 149.5 27.7 5868 134.5 -0.58 -0.28 0.52 100 43.8 20.6 13.3 12.1 14.77
Scorpion T510 1509 7.0 80.4 20.5 3465 72.4 -0.51 -0.21 0.32 100 14.8 3.9 2.2 2.0 13.13
Schuberth
Concept 1843 8.9 158.7 15.3 4120 142.9 -0.45 -0.15 0.24 85 11.0 2.9 1.7 1.5 13.50
Torc T14 1470 8.4 128.1 23.2 4334 115.3 -0.53 -0.23 0.35 100 20.7 5.6 3.3 2.9 15.32
Shoei RJ-Platinum 1211 8.5 237.2 10.9 5219 213.5 -0.41 -0.11 0.25 100 8.0 2.0 1.2 1.0 8.90
Bell shorty 8.8 215.9 30.8 7959 194.3 -0.61 -0.31 0.47 100 38.9 11.5 6.8 6.1 11.43
Daytona skull cap 711 7.1 388.9 38.5 23255 350.0 -0.69 -0.39 0.81 100 85.1 43.6 28.6 26.1 8.22
Fuel half-helmet 810 6.2 267.6 29.5 10665 240.8 -0.59 -0.29 0.46 100 38.3 11.6 6.8 6.1 11.45
HJC half-helmet 1079 8.4 256.7 11.4 5317 231.0 -0.41 -0.11 0.27 100 9.4 2.4 1.4 1.2 9.63
VCan V531 849 8.5 518.2 33.2 13234 466.4 -0.63 -0.33 0.51 100 46.5 14.7 8.7 7.8 6.58
Prototype 1171 8.8 126.3 6.5 2196 113.7 -0.37 -0.07 0.11 42 1.4 0.4 0.2 0.2 12.85
Note: * The best performing helmet for each variable is highlighted in green. * The worst performing helmet for each variable is highlighted in red
Table 1: Summary of results.
Figure 7: Risk of skull fracture associated with motorcycle helmet impacts.
Figure 8: Risk of concussion associated with motorcycle helmet impacts.
Figure 9: Risk of subdural hematoma associated with motorcycle helmet
impacts.
penetrating the brain. While skull fractures have been almost entirely
eliminated in activities such as American Football, the higher impact
speeds associated with motorcycle collisions continue to result in life-
threatening cranial fractures, even in areas covered by the helmet. us,
minimizing peak linear accelerations remains an important function of
any motorcycle helmet. erefore, to minimize the risk of skull fractures
associated with helmeted motorcycle collision, based on research by
Ono [13], a threshold of 140 g for peak linear acceleration to the frontal
and occipital areas of the head and 90 g for peak linear acceleration for
lateral impacts is suggested as a suitable performance criteria.
However, as with most helmets, motorcycle helmets perform
inadequately in terms of mitigating the forces responsible for causing
traumatic brain injury. ough a trend may exist between peak linear
acceleration and peak angular acceleration, a strong correlation is
absent, consistent with prior work in this area [28]. Hence, reduced
peak linear acceleration through improved helmet design may not
reduce the risk of traumatic brain injury. Indeed, as results herein show,
an unhelmeted individual may be at a lesser risk of subdural hematoma
during a moderate speed impact than one who is wearing a DOT [27]
approved motorcycle helmet.
To minimize the risk of traumatic brain injury, spanning from mild
concussion (AIS2) through severe brain injury (AIS5), it is necessary to
reduce impact-related peak angular velocities in the sagittal, coronal and
axial planes. Furthermore, since risk of subdural hematoma is dened
based on peak angular acceleration and impulse duration, reducing
Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets: Protection against Head and Brain Injuries. J Forensic Biomed 8: 135.
doi: 10.4172/2090-2697.1000135
Page 7 of 6
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
Figure 11: Motorcycle helmet effectiveness (presented in rank order from left
to right).
peak angular velocities while also managing impulse duration will also
lend to risk reduction of such severe or critical traumatic brain injuries.
erefore, to minimize the risk of concussion and subdural hematoma
in helmeted motorcycle collisions, it is suggested that performance
criteria based on peak angular velocity and acceleration not exceed
15.0 rad/s and 3,000 rad/s2, respectively, as previously proposed for
American Football helmets [29]
Figure 10 was prepared to illustrate the relative eectiveness of
the ten motorcycle helmet models tested and prototype in terms of
protection against skull fracture, concussion and subdural hematoma,
based on the above suggested performance criteria. Results indicate that
only the prototype provides adequate protection against both traumatic
head and brain injuries.
Based on the overall performance in terms of protection against
skull fracture, concussion and subdural hematoma, and assuming
equal weighting of these criteria for visualization purposes, the helmet
models are presented in rank order in Figure 11.
A strong negative correlation has been shown between helmet mass
and both peak linear and angular accelerations. is nding suggests
that ‘novelty’ motorcycle helmets (i.e., those not meeting FMVSS218 or
other motorcycle helmet standards), which are oen of lighter weight
than DOT-approved helmets [27], will likely perform poorly in terms
of preventing both head and brain injuries.
e new motorcycle helmet prototype evaluated within the scope
of this study demonstrated exceptional potential to minimize the risk
of traumatic brain injury, from mild concussion through severe brain
injury, for a helmeted motorcyclist involved in a collision of moderate
head impact speed.
Conclusion
e purpose of a motorcycle helmet is to reduce blunt force trauma
to the head, thereby decreasing the risk of lacerations, contusions and
skull fractures. Whereas brain injuries may be produced when the brain
lags behind sudden head motion thereby causing brain tissue, nerves
and blood vessels to stretch and tear. e type of brain injury sustained
is dependent on the magnitude and the time (pulse) duration over
which mechanical stresses and strains act on the brain.
Motorcycle helmet test standards focus on reducing forces
associated with linear acceleration by dropping helmeted headforms
onto an anvil from a stated height and measuring the resultant peak
linear acceleration. In general, the helmet design is considered
acceptable if the magnitude of peak linear acceleration is less than
an established threshold. us, helmets can and do prevent fatalities
associated with penetrating head trauma. However, it may be argued
that protection against brain injury is of paramount importance. Aer
all, cuts, bruises and even bone fractures will heal, but brain injuries, if
not fatal, oen have lifelong neurologically devastating eects.
Current helmet testing standards do not require performance
measures in terms of angular head kinematics and therefore fail to
address whether motorcycle helmets provide the necessary protection
against traumatic brain injuries. Research presented herein shows that
it is possible to sustain catastrophic brain injuries, even while wearing
a motorcycle helmet certied according to present testing standards.
Future generations of motorcycle helmets ought to be evaluated
at higher impact velocities that are more indicative of head impact
velocities in typical motorcycle accidents and should incorporate
measures of both linear and angular acceleration to quantify their
protective properties against both traumatic head and brain injuries.
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Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets: Protection against Head and Brain Injuries. J Forensic Biomed 8: 135.
doi: 10.4172/2090-2697.1000135
Page 8 of 6
Volume 8 • Issue 3 • 1000135
J Forensic Biomed, an open access journal
ISSN: 2090-2697
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Citation: Lloyd JD (2017) Biomechanical Evaluation of Motorcycle Helmets:
Protection against Head and Brain Injuries. J Forensic Biomed 8: 135. doi:
10.4172/2090-2697.1000135
