Ibitoye, A. B. USEP: Journal of Research Information in Civil Engineering, Vol 4, No.1, 2007
Hamouda, A.M.S.
Umar, R.S.R.
SIMULATION OF MOTORCYCLIST’S IMPACT
COLLISION ON ROADSIDE OBJECTS (GUARDRAIL)
*A.B. Ibitoye1, A.M.S. Hamouda2, R.S. R. Umar1
Road Safety Research Centre, Universiti Putra Malaysia
2
Department of Mechanical and Industrial System Engineering, Qatar
University, Doha, Qatar
*1
Abstract
In most motorcycling countries in Asia and Africa, where motorcycle are
widely used, complex safety problems arise as the roads and infrastructures
have not been developed at the same pace as motorcycle ownership and
traffic. Probability of the motorcyclists getting injured on collision with
roadside objects, such as guardrail, is higher compare to other motor
vehicles’ drivers. A standard Hybrid III dummy (50 th percentile male) was
used to mimic a worst crash impact a motorcyclist could sustain during
collision with roadside objects. Crash test scenarios were simulated and
some typical qualitative results on injury criteria and acceleration due to
head, thorax, and femur are presented. These results were compared to
human tolerance levels as prescribed in ISO 13232. Injury risks due to
impact with guardrail on curves were found to be more severe than impact
with guardrail along the straight portion of road or links. Also, head injuries
were found to be more severe than those to the legs or arms. Speed was
found to have greater influence on the injury risks to head, neck, chest and
femur. A greater reduction of severe injuries was found when the impact
speed changes from 60km/h to 32km/h.
Keywords
Simulation, motorcyclists, roadside, collision, guardrail
1. Introduction
A review of relevant literature revealed a significant safety risk to fallen
motorcyclists. Some studies carried out in USA, Canada, Germany and
Australia as published in Domhan (1987); Hell and Lobb (1993); Ouellet
(1982); Quincey et al (1988) and Transport Canada (1980) raised significant
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issues on motorcyclists’ impacts with crash barrier. Duncan et al. (2000)
raised a concern on the installation of guardrail that it can expose riders to
increased risk of injuries due to W-beam guardrail features, especially the
exposed edge of support posts. Impacts with guardrail posts are especially
harmful to motorcyclists as they cause injuries that are five times more
severe than an average motorcycle accident (Pieribattesti et al, 1999).
Ouellet (1982) observed that every rider that struck guardrail suffered at
least multiple extremity fractures. Most motorcycle collisions with crash
barriers occur at shallow angles with the rider typically sliding into the
barrier at a bend (Quincy et at, 1988).
Most motorcycle accidents occur at relatively low speeds, although fatal
and serious injuries are more likely to be suffered at higher speeds. Pang et
al., (2000) found that the most common causes of crashes are speeding, not
paying attention and loss of control, run-off the road because of excessive
speed, fatigue or inattention. Majority of motorcycle collisions take place at
fairly low speeds, between 30 and 60 kilometers per hour (EEVC, 1993).
Mannering et al, (1995) found that almost all (93%) of the serious and fatal
head injuries occur at speeds of up to 64km/h. Skull fractures may occur at
speeds of 30 km/h or more, but brain injuries may happen at much lower
speeds, from 11 km/h upwards. Approximately 75% of motorcycle
accidents occur at impact speeds of up to 48km/h and 96% at up to 64 km/h
(Mannering et al, 1995).
However, the greater severity of injuries presented by barriers and posts is
due to the fact that they often present rigid surfaces that are perpendicular to
the motion of the rider. Domhan (1987) reported that severe injuries are
sustained by two out of three motorcyclists who collide with guardrail with
most dangerous features of guardrail systems being the guardrail posts. The
chances of injury sustenance upon hitting a fixed object are related to the
impact area and the rigidity of the object (Gibson & Benetatos, 2000). Thus,
impacts with small rigid objects are more likely to cause injury because the
small impact area increases the stress upon the impact portion of the
motorcyclists (Domhan, 1987). Since motorcyclists lack protection of an
endorsed vehicle, they are likely to sustain serious injury or even get killed
if their motorcycles crash with rigid object on road. The most likely areas of
the body to be injured for motorcyclists in collisions are in order, the legs,
heads, and thorax (Hell and Lob, 1993).
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The main purpose of this study is to investigate the effect of impact speed
and impact angle on the injury risks to motorcyclists as exist in the real
world traffic accidents. But due to lack of data on such accidents, the impact
scenario of this collision was simulated using computer simulation package.
Outcome of the study may serve as a basis for designing a more forgiving
guardrail for safer motorcycling. The next section of this paper discusses
the material and methods of achieving this objective and discusses the
implications of the obtained result as compared to human tolerance levels.
2. Simulation Models
This study was based mainly on a computer simulation developed to
investigate effect of motorcycle impact collision with roadside guardrail on
the motorcyclist. Simulation process involved modelling of four systems
including road as inertia reference space as well as crash interaction of these
systems. The other three systems are the motorcycle, dummy and guardrail
models, which are also described in the following sections.
2.1 Reference Space
A plane surface road was used as the reference space on which the
coordinates of other three systems were connected. The coordinate of the
road surface was defined with three points. The first two points represent
the vertices on one edge of the rectangle and the third point is on the
opposite edge of rectangle. MADYMO program calculates the remaining
vertices on the opposite edge to complete the rectangular shape. The origin
and orientation of this reference space was selected with the positive Z-axis
vertically upward, positive X-axis chosen along the direction of travel and
the positive Y-axis is then chosen to the right. The motion of all other
systems was defined relative to this coordinate system.
2.2 Motorcycle Model
A KRISS SG motorcycle type of size 110cc produced by Modenas
Malaysia Bhd was chosen as a design motorcycle because it is most
commonly used motorcycle in Malaysia. This motorcycle was modelled as
a multi-body system with four rigid bodies interconnected by kinematics
joints. In multi-body dynamic methods, body fixed coordinate frames are
generally adopted to position each one of the system components and to
allow for the specification of the kinematics constraints that represent the
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restrictions on the relative motion between the bodies (Ambrosio et al,
1996).
For modelling the motorcycle, the body local coordinate system was chosen
based on the assumption that motorcycle bodies move symmetrically about
the longitudinal axis. This implies that the centre axis of each body is
parallel to the centreline of the road, which is the reference space for the
system. The motorcycle was then modelled to move with a steady speed on
a straight line prior to impact. Data corresponding to each specific body was
then defined with respect to this body local coordinate system. As the study
is primarily concerned with predicting motorcyclists’ injuries due to
impacts rather than motorcycle crashworthiness, the assumption is valid as
asymmetrical movement of motorcycle may result in its instability during
impact with guardrail at a predefined impact point. Therefore, this system of
bodies was then defined by the bodies, surface, kinematics joints and initial
conditions as described briefly in the following subsections.
2.2.1
Bodies
Each of the four motorcycle bodies were defined by the mass, inertia matrix
and the location of the centre of gravity. The geometry and mass of the real
motorcycle (Fig. 1) were measured in the laboratory and the values obtained
were compared to the manufacturer’s specifications. The wet weight of
motorcycle (110 kg) was considered in this study and this includes an
increase of 14kg added to the specified dry in order to compensate for the
topped up fuel and other fluids as exists in real life situation.
900
150
1050
415
550
545
1245
1950
Dimensions in mm
Fig.1. Schematic drawing of motorcycle model.
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The inertia matrix and location of the centre of gravity were defined in
accordance to MADYMO Reference Manual (MADYMO, 2004). The
inertia matrix of each rigid body of motorcycle was determined using the
conventional equations for regular shaped bodies as contain in Ferdinand
and Johnston (1995). Since the local coordinate system for each body was
chosen at the location of its joint corresponding to the centre line of the
reference space (road), the location of centre of gravity of each body was
then expressed in the local coordinate system of the body. This implies that
the local coordinates of body corresponding to the joint coordinates of
bodies were used to calculate the motion of the body coordinate systems
relative to the reference space coordinate system.
In this study, a joint coordinate system was defined parallel to the local
coordinate system of the body to which it is attached. The free joint
between the reference space and the frame body allows the motorcycle to
translate parallel to the road. The revolute joint between the front fork and
the frame has axis of the joint coordinate system parallel to the rotation axis
by default. The axes of the joint coordinate systems of the front and rear
wheel revolute joints are made parallel to the y-axes of the corresponding
body coordinate systems so that they coincide with the wheel rotation axes.
2.2.2
Surfaces
As available within the software codes, body surfaces consisting of
rectangular planes, ellipsoids and elliptical cylinders are always attached to
any body of the system to represent its shape. The surface of the modelled
motorcycle was then represented with ten regular shapes consisting of two
ellipsoids for main frame, one ellipsoid for upper part of front fork and two
ellipsoids and cylinders for the two wheels as shown in Figure 1. Other
ellipsoids were used to represent handle bar, foot rest and leg cover.
In this study, ellipsoids of the main frame were attached to the rectangular
plane of the reference space (road) while the ellipsoids of front fork, the rear
and front wheel were attached to the main frame. The orientation of the
cylinder coordinate system for tyres was specified in accordance to the
codes so that the motion of the tyre relative to the road was described with
respect to the road coordinate system. The MF-MC Tyre model available in
MADYMO codes for motorcycle tyres was used to model the wheels. This
tyre model was based on the physical background of the tire, road, and the
tire-to-road contact for accurate description of the steady-state behaviour of
the tyre. The tyre was represented with a cylindrical disk connected to a
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modelled rigid body called wheel. The centre of this disk coincides with the
wheel centre.
2.3 Crash Dummy Model
The dummy used in this simulation model was a non-helmeted standard 50th
percentile adult male Hybrid III MADYMO dummy to represent the rider
and to mimic the trajectory, acceleration and impact deformation experience
by a human during crash impact. MADYMO has been shown to be a very
competent tool for the prediction of human response and the calculation of
occupant injury criteria (Troutbeck et al., 2001). The description of the used
Hybrid III 50 percentile dummy is summarized in Table 1.
Table 1 Description of Hybrid III Dummy
Basis dummy
Hybrid III 50 percentile
Overall height
Male
Mass
1720 mm
Bodies
54.9kg
Joints
30
Ellipsoids
29
28
However, the dummy segments were positioned in such a way that
replicates the posture of a real life rider. These segments include; the
dummy’s shoulder, Hips, Knees, and Ankles. In addition, the same initial
velocities and initial position body acceleration defined for motorcycle were
also defined for the dummy. Thus, the dummy was able to mimic the
trajectory, acceleration and impact deformation experience by a human
during crash impact.
2.4 Guardrail Model
The existing w-beam guardrail system was composed of w-shaped, 12gauge, galvanized steel rail attached to posts embedded into the soil at space
interval of 2m and 4m. The description of this guardrail type shown in
Table 2 was based on the longitudinal barrier design guidelines produced by
Malaysia Ministry of Public Works (JKR). The guardrail manufacturers in
Malaysia also based their production on this specification.
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Table 2. Description of existing guardrail model.
Standard
Beam
Posts and
Block-outs
Parameters
Overall Length
Effective Length
Beam Thickness
Effective Depth
Values
4318 mm
4000 mm
2.67 mm
312 mm
1830 x 178 x 76
Post dimensions
(710mm above ground)
Block-out dimensions
360 x 178 x 76 (6mm thick )
Post spacing
2000 mm and 4000 mm
(Source: JKR, Arahan Teknik, 1993)
Since the study’s main aim is to assess the rider’s injury risks rather than
assessment of roadside barriers, MADYMO software was used only to
characterize the dynamic response of guardrail structure while the stress
concentration effect was ignored.
Finite element method was used to reduce guardrail structure to discrete
numerical model. Out of many elements that are available in MADYMO;
trusses, beams, membranes, shells and solids, four-node shell element was
used to model guardrail surface. This element was chosen because of its
suitability for the analysis of dynamic behaviour of guardrail structure
which results in dynamic response of motorcyclist as investigated in this
study.
Four-node shell element is a two-dimensional quardrilateral element that
connects four nodes and carries in-plane loads as well as bending loads.
This element is based on bi-linear displacement and rotation interpolation.
In order to prevent element distortion, aspect ratio checks were carried out
on the element shape. Any distortion in element could result in element with
either zero or negative stiffness terms that could cause fatal error in element
subroutine or global solution routine. In addition, an effective hourglass
control algorithm available in MADYMO was used to suppress the
hourglass modes. These hourglass modes could occur due to lack of enough
deformation parameters in relation to the nodal degree of freedom because
of reduced integration.
In MADYMO Lagrange integration method is used to describe nodes and
elements, which are fixed to the material and thus move through space with
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the material. Material property for steel was then defined for the existing
guardrail while properties of composite materials considered for alternative
designs were also defined. The finite element mesh of 4.318m length wbeam guardrail structure modelled in this study is as shown in Fig. 2.
Fig. 2. Finite element mesh for W-beam guardrail (4.318m length)
3. Crash Simulation
Crash simulation was carried out to identify problems that may impact
safety of motorcyclists as reported in literatures. This simulation made use
of crash scenario similar to real life motorcycle collision with guardrail.
That is, a motorcycle model with a dummy in an upright position colliding
with 4m post spacing w-beam guardrail oriented at 45o to the travel
direction. The complete simulated model is as shown in Fig. 3.
DUMMY
W-BEAM GUARDRAIL
ROAD
MOTORCYCLE
Fig. 3. Complete simulation model
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The impact speeds of 32km/h, 48km/h and 60m/h were assumed as impact
forces from motorcycle wheel on the guardrail nodes. This impact forces
were converted into point loads acting at the nodal points to cause dynamic
displacement of guardrail and subsequent ejection of motorcyclist. The
contact point on the guardrail mesh by the motorcycle wheel is thus
illustrated in Fig. 4.
End Support 1
End Support 2
45o
Point load
Fig. 4. Motorcycle wheel impact force on guardrail nodes
4. Simulation Results
The simulation results were evaluated based on rider’s kinematics for the
assessment of potential injury risk in order to establish critical injury risks.
Therefore, only the trajectories of rider were used to illustrate effect of
kinematics on the potential injury risks to rider while the kinematics of
motorcycle is hidden.
Fig. 5 illustrates effect of rider’s kinematics due to motorcycle collision at
various speeds on guardrail which was oriented at angles 45 degree to the
travel direction. The effect of these impacts with the guardrail mid span was
tested for both 2m and 4m post spacing. In the entire crash scenario rider
was observed sliding and tumbling over the top of the guardrail. The first
contact of rider’s body was with the guardrail surface. This contact was
with the lower extremities which caused forward acceleration of rider due to
loading from the pelvis through motorcycle seat and guardrail surface.
These interactions alter the trajectories of the rider. The first contact
resulted in a turning moment about the centre of gravity of the rider causing
the upper body to arc downward. The next contact point was the ground as
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the rider finally landed on ground. The rider landed on the ground with
direct blows on the head or face at various angles to the horizontal due to
decelerating speed
0s
0.2 s
0.3 s
0.4 s
Landing
Speed
32 k/h
48 k/h
60 k/h
Fig. 5. Comparing rider’s kinematics at 45 degree for 4m spacing
From the Figure, the rider can be observed to suffer lower extremity contact
with guardrail surface showing the effect of speed on rider’s movement.
Also, in each scenario, the dynamics of the rider’s fall to the ground were
different. The orientation of head increases with speed, while the trajectory
time for the head to have ground impact decreases with speed. This implies
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that the possibility of the rider landing on ground with other part of the
body (hand or leg) during higher impact speed is evidenced.
Since the rider is ejected head forward and has head contact with ground,
the most severe injuries that were generated are related to the head. Head
injuries appears to be the most life threatening form of injury for
motorcyclists and are predominantly caused by direct impact of head to the
ground. The impact force on the head is commonly described with HIC and
head acceleration to express the human tolerance. HIC rates the severity of
head contact and its reduction is associated with reduction of brain shear
stress (Ruan and Prasad, 1995).
The potential injuries risks to the head, neck, chest and lower extremities
were evaluated in this study with the associated tolerance levels. Head
Injury Criterion (HIC) of 1000 and head acceleration of 80g as the threshold
for brain trauma. The injury criteria for the neck were based on tension,
compression, shear and bending moment. The tensile and shear load limit is
with the value of 1100 N (duration > 45 ms); the compression limit of 5700
N while bending limit of 190 Nm in flexion and 57 Nm in extension were
used. Chest injuries are evaluated according to the criterion of 60 g while
femur force criterion of 10 KN was used to evaluate leg injuries. The
summary of all these injury risk values are presented in Tables 3.
Table 3: Potential injury risks at impact angle 45o
Injury
Parameters
Biom.
Limit
HIC
Head (a3ms)
3 MS (Chest)
FNIC_tension
FNIC_shear
FNIC_bendng
FFCL
FFCR
1000
80 g
60 g
1.1KN
1.1KN
57Nm
10 KN
10 KN
32 km/h
2m
4m
span span
Impact Speed
48 km/h
60 km/h
2m
4m
2m
4m
span span span
span
2899
310
16
3.5
0.6
37
1.6
3.3
3102
332
27
5.8
0.5
37
8.6
4.1
2848
248
14
2.9
1.2
53
1.2
0.4
NC = No head contact with ground
115
2963
317
24
4.8
0.3
26
4.9
1.7
25-NC
14-NC
10
0.6
0.3
26
13.6
2.9
11-NC
12-NC
9
0.5
0.1
19
4.2
3.3
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Table 3 shows increase in the values of HIC, head acceleration and tension
in the neck as speed increases. This indicates that the downward impact on
the head has effect on the neck. This impact can either flexes or extends the
neck to fracture or dislocate the vertebrae and damage the spinal cord
(Viano and King, 1996). Thus, the measured injury values exceeded the
corresponding biomechanical limits of HIC=1000, head acceleration = 80g
and neck tension force =1.1KN. The neck tension force also increases with
speed except at 60 km/h due to no head contact of rider on ground. Other
injury risks values to the chest, neck bending and shear are lower than their
tolerance values. The measured risk values for femur are also less than
biomechanical except for the left femur at speed 60 km/h (13.6KN) at 2m
post spacing that are higher than the limit of 10KN. This indicates the
severity of leg interaction with 2m span guardrail at higher speeds.
5. Discussion
Injuries to head such as HIC and head acceleration were found to be higher
than tolerance level for all impact condition where head impact with
ground. This result implies that the rider may suffer skull fractures and
brain injuries in agreement to FEMA (2005) report that skull fracture may
occur at speed of 30km/h or more. It also confirms the finding of Hell and
Lobb (1993) that injury risks to the head are more severe than that of other
part of the body. This result also agrees with the findings of Tabiei, and Wu,
(2000) that contact of the head and neck with the hard road surface
generally results in fatalities or catastrophic injuries. Most of these injuries
occur as the rider slides and tumbles along the top of guardrail before
landing on the ground with head. This result agrees with the report of
Ouellet (1982) that motorcyclist remaining upright during impact tend to
slide and tumble along top of the posts supporting safety barrier.
Apart from injuries to head and neck, other part of rider’s body such as
lower extremity also has contact with the guardrail surface as the rider
slides sideway during collision before ejection but they are not as severe as
head injury risks. Ouellet (1982) in a study noted that although this type of
body contact is frequent, it is not as severe as head contact with the road
surface. The greater severity presented by the guardrail is as a result of their
rigid surfaces which are perpendicular to the motion of the rider (Ouellet,
1982). The reason for these hazards has been attributed to include non
consideration of motorcyclists in the crash testing standard (EEVC, 1993).
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Thus, the future evaluation of guardrail performance needs to consider
motorcycle impact for such guardrail to be used in protecting motorcyclists.
6. Conclusion and Recommendation
This study has been able to investigate the effect of impact speed and angles
on crash injury due to motorcycle impact with guardrail using computer
simulation. Thus, this paper has been able to highlight that:





Kinematics of rider is similar during the initial stage with the
dummy having leg contact with the guardrail surface and
projecting with head forward. However, the dynamics of rider
towards the landing depend on the impact speeds and angles.
Generally, for all impact conditions considered in the crash
simulation, the rider fall to ground with head except for impact
speed of 60km/h. This indicates that head injury risks is most
critical to motorcyclists and that high vaulting of rider at higher
impact speed can cause rider to land on any part of body rather
than the head.
The study has been able to establish the fact that the severity of
impact increases with speed. This implies that guardrail orientation
at angle 45o with impact speed of 48km/hr at 2m and 4m post
spacing appears to be the worst impact condition.
The injury tolerance level was found to be critical to the head than
any other part of the body. Therefore, the tolerance level values of
HIC =1000 and Head acceleration=80g can also be considered as
threshold for future assessing of potential injury risks to rider.
Therefore, the need to improve certain features of existing
guardrail that impact motorcyclist’s safety is therefore
recommended.
7. Acknowledgment
The authors are indebted to the Ministry of Science, Technology and
Environment for funding this work through an IRPA Grant. We would like
to express our deep appreciation to members of Road Safety Research
Centre, Universiti Putra Malaysia who have contributed in various ways to
the success of this study.
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