Accident reconstruction expert Dr. John Lloyd has served attorneys nationwide for 25+ years in biomechanics, human factors, helmet testing and motorcycle expert
Motorcycles are highly sensitive to changes in roadway conditions. Potholes can destabilize a motorcycle, causing the rider to lose control. The following is a case in which a rider claimed he was traveling at only 15 miles per hour, when he came upon a large pothole in the roadway and lost control. The motorcycle fell to the right, with the right foot peg penetrating the rider’s leg, leading to a near amputation of his right foot. Dr. Lloyd was retained to investigate the cause of the motorcycle pothole crash.
Test Instrumentation
An exemplar Honda CBR 929RR motorcycle was acquired and instrumented with accelerometers installed on the front axle, rear axle and handlebars:
Data acquisition was controlled using a National Instruments cDAQ 9178 and acquired at 10 kHz per channel on a Windows tablet running LabVIEW software:
Pothole Crash Testing
Using the instrumented motorcycle, Dr. Lloyd constructed an exemplar pothole in an open parking lot using ramps to investigate how the length and depth of the pothole affected stability of the motorcycle. In addition to sensors, testing was recorded using high speed and standard video, as well as GoPro cameras mounted on the motorcycle
Results
Based on analyses and physical evidence, that the speed of the motorcycle while crossing the roadway defect was likely 14 -18 miles per hour. At such speeds, the front and rear suspensions have a tendency to approach maximum compression. along with substantial deformation of the tires.
Conclusions
Dr. Lloyd determined that the motorcycle crash was caused due to the motorcycle accelerating as it crossed the pothole. When the rear wheel crossed the fore edge of the defect it lost contact with the roadway and the rear wheel speed increased without resistance. Upon contact with the aft edge of the roadway defect the rear wheel was at a higher rate of speed than the rest of the motorcycle, causing the motorcycle to unexpectedly wheelie.
Please call Dr. Lloyd at 813-624-8986 or email DrJohnLloyd@Tampabay.RR.com to discuss how he can be of help to you with your case.
The following is a case study in which biomechanics expert, Dr. John Lloyd, evaluated the risk of concussion and brain injury associated with headrest impact in rear end crashes.
Headrest Impact Test Apparatus:
In accordance with prior published test methods[1],[2],[3], a test apparatus was constructed to evaluate the biomechanical protection afforded by an exemplar automobile headrest against head and brain injuries during occipital head impacts in a simulated rear-end motor vehicle collision.
The apparatus involves a pendulum arm, attached by bearing housings to a weighted base. The upper body, including neck and head of a 50th percentile Hybrid III crash test dummy was mounted to the pendulum arm. Data acquisition was initiated by triggering an electromechanical release mechanism, allowing the mannequin to fall, under acceleration due to gravity, until the crash test dummy impacted the headrest and backrest (Figure 1).
Figure 1: Test apparatus
The fundamental elements and principles of this testing have been utilized in other laboratories. By utilizing a Hybrid III neck, the head impact tests are more realistic, causing head rotation at the axis between the head and neck, which produces measures of head and brain angular kinematics. The methods presented herein are based upon standardized test methodologies and published research.
Instrumentation
Four PCB Piezotronics tri-axial accelerometers (model # 356A01) were mounted in an X,Y,Z array at the center of mass of the Hybrid III headform, along with a tri-axial angular rate sensor produced by Diversified Technical Systems (composite Figure 2).
Figure 2: Sensor installation in Hybrid III headform
Sensor Calibration:
All sensors were calibrated by the manufacturer. Verification of calibration of the linear accelerometers was performed prior to testing using a calibration shaker. Results indicate that the sensors were operating in the specified frequency range and output (Figure 3).
Figure 3: Pre-test verification of linear accelerometer sensors
For the angular rate sensor, a simple validation method was devised in which the sensor was affixed to a digital goniometer that was rotated through a 90-degree angle. Using LabVIEW software, the integral of angular rate was computed, reflecting concurrence with the digital goniometer for all three planes of motion (Figure 4).
Figure 4: Pre-test validation of angular rate sensor calibration
Headrest Impact Testing:
The mannequin head was raised from the headrest in 2-inch increments from 2 inches to 30 inches, generating head impact speeds from 1 to 25 miles per hour. Two headrest positions were evaluated, along with two different Hybrid III necks representative of a stiff and relaxed neck (Figure 5), for a total of sixty tests.
Figure 5: Test apparatus with Hybrid III loose neck and headrest in lower position
Data Acquisition and Analysis:
Data from the analog sensors were acquired in accordance with SAE J211 [4], using a National Instruments compact DAQ data acquisition system and LabVIEW software (National Instruments, Austin, TX). The raw data was then filtered in MATLAB (The MathWorks, Natick, MA) using a phaseless eighth-order Butterworth filter with cutoff frequencies of 1650 Hz and 300Hz for the linear accelerometers and angular rate sensors, respectively.
Angular acceleration values for sagittal, coronal and axial planes were computed from the angular velocity data using the 5-point central difference by least squares method (Equation 1):
Equation 1: Five-point central difference by least squares method
Angular acceleration vales were also derived from the array of linear accelerometers, by the mathematical method documented by Padgaonkar et al [5].
Linear velocity was calculated by integrating linear acceleration. Mathematical methods were performed using Matlab to compute characteristic values from variables of interest. Figure 6, below illustrates peak linear acceleration and angular velocity associated with a 6.8 mph occipital head impact against a headrest.
Figure 6: Linear acceleration and angular velocity associated with headrest impact
It is noted that the major component of linear acceleration was in the X-axis (anterior-posterior), while the major component of angular velocity was in the sagittal plane, as expected.
Linear acceleration values were used to calculate Maximum Pressure (Equation 2), Gadd Severity Index (GSI) (Equation 3), and Head Injury Criterion (HIC15) (Equation 4).
Equation 2: Maximum Pressure
Equation 3: Gadd Severity Index
The Head Injury Criterion (HIC) is an empirical measure of impact severity describing the relationship between the linear acceleration magnitude, duration of impact and the risk of head trauma (Equation 4).
Equation 4: Head Injury Criterion
where a is resultant head acceleration, t2-t1 < 15 msec
With reference to the Figure 7, below, the HIC value is used to predict the risk of head trauma: Minor –skull trauma without loss of consciousness; nose fracture; superficial injuries Moderate – skull trauma with or without dislocated skull fracture and brief loss of consciousness. Fracture of facial bones without dislocation; deep wound(s) Critical – Cerebral contusion, loss of consciousness for more than 12 hours with intracranial hemorrhaging and other neurological signs; recovery uncertain.
Figure 7: Probability of specific head trauma level based on HIC value
Peak angular velocity was determined as the maximum angular velocity related to peak linear acceleration impact time. Angular velocity values were used to derive Maximum Principal Strain (MPS) (Equation 5), Cumulative Strain Damage Measure (CSDM) (Equation 6), and Brain Rotational Injury Criterion (BrIC) (Equation 7).
Equation 5: Maximum Principal Strain
Equation 6: Cumulative Strain Damage Measure
An analysis method validated by Takhounts [6] establishes physical injury criteria for various types of traumatic brain injury and uses Anthropomorphic Test Device (ATD) data to establish a kinematically based brain injury criterion (BrIC) for use with ATD impact testing. This method was utilized to express risk of diffuse brain injury according to the revised AIS scale [7] in terms of peak angular head kinematics, where:
Equation 7: Brain Rotational Injury Criterion
Headrest Impact Results:
A summary of key results is presented in Table a-d, below. The driver was aware of the pending impact, as he depressed the accelerator in an attempt to avoid the collision in the moments prior to the crash. In rear end collision tests involving human subjects, volunteers instinctively tensed their neck muscles as a protective response. Given that the driver anticipated the crash his neck muscles were likewise expectedly tense as an instinctive protective response. Therefore, the results most consistent with the subject case are presented in Tables a and b. Rows highlighted in green are consistent with change in velocity experienced by the driver during the subject crash.
Table a: Summary of test results – Neck – Stiff; Headrest – lower position
Table b: Summary of test results – Neck – Stiff; Headrest – upper positio
Table c: Summary of test results – Neck – Loose; Headrest – lower position
Table d: Summary of test results – Neck – Loose; Headrest – upper position
Skull Fracture
With reference to Ono 8, none of the impact tests approached the occipital skull fracture threshold of 140 g for impacts lasting longer than 7 milliseconds. Therefore, vehicle headrests provide excellent protection against acute skull fractures at impact speeds below 25 mph.
Traumatic Head Injury
With reference to Figure 7 and Tables a-d, maximum recorded HIC values were consistent with a 5 percent or less risk of moderate traumatic head injury. Whereas, the HIC value computed at impact speeds similar to the crash was only 3.4, at which the risk of minor or moderate traumatic head injury is negligible.
Mild Concussion
With reference to Figure 8 below, the risk of an occupant sustaining a mild concussion in a rear-end collision producing a change in velocity of 6.25 mph (range 5.4 to 7.2 mph) can be determined based on the following calculation: Risk AIS-1 = 31.744*ln(x) + 6.1748 (R2=0.67). The risk of and AIS-1 mild concussion, without post-concussion syndrome, in such an impact is 64.3% (range 59.7 to 68.8%).
Figure 8: Risk of mild concussion (AIS-1) associated with headrest impact
Severe Concussion
With reference to Figure 9, below, the risk of an occupant sustaining a severe concussion in a rear-end collision producing a change in velocity of 6.25 mph (range 5.4 to 7.2 mph) can be determined based on the following calculation: Risk AIS-2 = 0.198e0.234x (R2=0.85). The risk of severe concussion in such an impact is 0.85% (range 0.70 to 1.07%).
Figure 9: Risk of severe concussion (AIS-2) associated with headrest impact
Traumatic Axonal Injury:
Figure 10, below, is adapted from Margulies et al. 20 in which thresholds for axonal injury were developed and published based on mathematical modeling, animal testing and physical experiments. Results from occipital head impact against an exemplar headrest at a speed of 6.2 miles per hour are represented, indicating that rotational head and brain kinematics associated with such impact are well below scientifically-accepted thresholds for traumatic axonal injury.
Figure 10: Scientific Thresholds for Axonal Injury
Figure 11, below was generated from data presented in Tables a through d, to present the risk of traumatic axonal injury associated with head impact against an headrest.
Figure 11: Risk of traumatic axonal injury (AIS-4) associated with headrest impact
Results show that the risk of an occupant sustaining traumatic axonal injury in a rear-end collision producing a change in velocity of 6.25 mph (range 5.4 to 7.2 mph) can be determined based on the following calculation: Risk AIS-4 = 0.0271e0.2391x (R2=0.85). The risk of traumatic axonal injury in an impact of the magnitude experienced by the driver is 0.12% (range 0.10 to 0.15%).
Conclusions
Biomechanical testing of head and brain injury risk associated with occipital head impact against a headrest, in accordance with published methods, shows a significant risk (59.7 to 68.8%) of AIS-1 mild concussion, without post-concussion syndrome, in a 6.2 mph rear-end collision. However, the risk of an AIS-2 severe concussion in such an impact decreases to 0.70 to 1.07%, and the risk of traumatic axonal injury is only 0.10 to 0.15%. Moreover, the mechanical traumatic axonal injury is not consistent with a sagittal plane impact.
References
[1] Caccese V, Lloyd J, Ferguson J (2014) An Impact Test Apparatus for Protective Head Wear Testing Using a Hybrid III Head-Neck Assembly. Experimental Techniques.
[2] Lloyd J & Conidi F. (2015). Brain Injury in Sports. Journal of Neurosurgery. October.
[3] Lloyd J. (2017). Biomechanical Evaluation of Motorcycle Helmets: Protection Against Head and Brain Injuries.Journal of Forensic Biomechanics.
[4] SAE (2014) J211/1. Instrumentation for Impact Test – Part 1 – Electronic Instrumentation. Society of Automotive Engineers International, Surface Vehicle Recommended Practice, Warrendale, PA.
[5] Padgaonkar AJ, Krieger KW and King AI. Measurement of Angular Acceleration of a Rigid Body using Linear Accelerometers. J Applied Mechanics. Sept 1975.
[6] Takhounts EG, Craig MJ, Moorhouse K, McFadden J (2013) Development of Brain Injury Criteria (BrIC). Stapp Car Crash Journal 57: 243-266.
[7] Abbreviated Injury Scale (2008) Association for the Advancement of Automotive Medicine, Des Plaines, IL.
A solo motorcycle crash is one of the leading causes of motorcycle accidents. These accidents are unique in that, typically, no other vehicles are involved. Oftentimes the root cause is rider error due to the fact that motorcycles are considerable more complex to operate than passenger vehicles.
Riders involved in a solo motorcycle crash typically fit one of two categories:
Riding too fast
Inadequate experience
The first category speaks for itself. Riding too fast for conditions reduces time and distance available to respond safely to potential hazards, such as other roadway users.
Lack of experience includes lack of appropriate training or failure to maintain training. Many riders purchase an expensive motorcycle – far too powerful and heavy for their riding abilities – and ride less than 3000 miles per year – generally in a straight line. When they are faced with a hazard, they panic and make poor choices, all too often resulting in injury or death.
Motorcycle Braking
Unlike cars, the front and rear brake systems on a motorcycle are typically independent — the front brake is operated by a lever on the right side of the handlebar, while the rear brake is operated by a foot pedal, also on the right side. As car drivers we learn that hard braking is performed by the right foot. However, doing so on a motorcycle will inevitably lead to trouble. In fact, about 70 percent of the braking power on a motorcycle comes from the front brake lever.
As front brake force increases weight transfers to the front tire, increasing the tire force acting on the road surface, which permits application of even greater front brake force.
However, sudden over-braking on the front, on a motorcycle not equipped with ABS, can produce a front-tire skid, which can cause loss of control in under one second. So, for an inexperienced rider it can be challenging to find the ‘sweet-spot’ between hard braking and over-braking on the front tire.
Whereas, utilization of the rear brake without the front brake produces only 30% braking efficiency and can cause the rear end of the motorcycle to skid and ‘fishtail’, due to the fact that there is generally less weight and a larger contact area (less pressure) on the rear tire.
Experienced motorcyclists learn to use both the front and rear brakes in unison and, together both brakes can out-perform the stopping power of most other roadway vehicles.
Motorcycle Steering
Motorcycles also differ from other vehicles in the way that they steer. In a car if you want to go right you turn the steering wheel to the right and visa versa. Whereas, on a motorcycle if you want to go right you turn the handlebar to the left. On the surface this appears to be counter-intuitive. However, due to the geometry of motorcycles, when you turn the handlebar in one direction, the bike will lean in the opposite direction. It is this lean that causes the motorcycle to turn. This phenomenon is called counter-steering.
To turn a tighter curve you simply increase the lean angle. Modern sport motorcycles are capable of lean angles up to 60 degrees, allowing motorcycle racers to turn corners at high speeds. However, most curves on public roads don’t require more than 15 degree lean angle, which is generally the comfort limit of many novice riders.
In 2016 there were more than 8.4 million motorcycles registered in the United States, representing 3.2% of all US vehicles. California, Florida and Texas were the leading States in terms of the motorcycle popularity; collectively representing 22% of all US registered motorcycles. According to the U.S. National Highway Traffic Safety Administration (NHTSA), 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.
Number One Cause of Motorcycle Crashes
Seventy-five percent of accidents were found to involve a motorcycle and a passenger vehicle, while the remaining 25% of accidents were single motorcycle accidents.
The number one cause of motorcycle crashes is a motorist making a left turn across motorcycle path. With reference to the Hurt report in the United States and the MAIDS in-depth investigation of motorcycle accidents in Europe, approximately two-thirds of all motorcycle crashes involving other vehicles are caused due to violation of the motorcycle rider’s right of way by the failure of motorists to detect and recognize motorcycles on the road.
While the motorcycle rider has right of way, they are also more vulnerable to injury. Motorcyclists must therefore be extra-vigilant, especially when approaching intersections. Appropriate riding gear, including a DOT certified helmet, motorcycle jacket and riding boots offer the motorcyclist the best protection. Findings of the Hurt study indicate that severity of motorcyclist injury increases with speed, alcohol consumption, motorcycle size and speed.
Motorcyclist Conspicuity
Conspicuity is one of the key factors in motorcycle road crashes around the world. The inability and difficulty of other road users in detecting motorcycles either at day or at night has contributed to conspicuity related motorcycle crashes. Additional lights and brightly colored riding gear can help to improve motorcyclists conspicuity to other roadway users. The following image depicts this author wearing a hi-visibility motorcycle jacket and helmet to enhance conspicuity.
Please call Dr. Lloyd at 813-624-8986 or email DrJohnLloyd@Tampabay.RR.com to discuss how he can be of help to you with your case.
To consider whether a motorcycle helmet might reduce the risk of brain trauma in a motorcycle accident it is first important to understand the two primary mechanisms associated with traumatic brain injury – impact loading and impulse loading, according to motorcycle helmet expert, Dr. John Lloyd.
Impact loading involves a direct blow transmitted primarily through the center of mass of the head, resulting in extracranial focal injuries, such as contusions, lacerations and external hematomas, as well as skull fractures. Shock waves from blunt force trauma may also cause underlying focal brain injuries, such as cerebral contusions, subarachnoid hematomas and intracerebral hemorrhages.
Whereas, impulse or inertial loading caused by sudden movement of the brain relative to the skull, produces cerebral concussion. Inertial loading at the surface of the brain can cause subdural hemorrhage due to bridging vein rupture, whereas if affecting the neural structures deeper within the brain can produce diffuse axonal injury (DAI).
Epidemiology Studies
Two major epidemiologic studies into the causation of motorcycle accidents have been conducted in North America and Europe: the Hurt Report and the MAIDS report. The Hurt Report showed that failure of motorists to detect and recognize motorcycles in traffic is the predominating cause of motorcycle accidents. Seventy-five percent of accidents were found to involve a motorcycle and a passenger vehicle, while the remaining 25% of accidents were single motorcycle accidents. Two-thirds of motorcycle-car crashes occurred when the car driver failed to see the approaching motorcycle and violated the rider’s right-of-way. Findings indicate that severity of injury increases with speed, alcohol motorcycle size and speed.
The MAIDS study (Motorcycle Accidents In Depth Study) is the most recent epidemiologic study of accidents involving motorcycles, scooters and mopeds, which was conducted in 1999 to investigate motorcycle accident exposure data across five European countries. Key findings show that passenger cars were the most frequent collision partner (60%), where 69% of the drivers report that they did not see the motorcycle and the predominance of motorcycle accidents (54.3%) occurred at an intersection.
In 1995, the European Commission Directorate General for Energy and Transport initiated a Cooperative Scientific and Technical Research (COST) program to investigate Motorcycle Safety Helmets. Several agencies from Finland, the United Kingdom, France and Germany participated in this study, which compiled and analyzed data from 4,700 motorcycle fatalities in Europe, each year. The COST report documents that 75% of all fatal motorcycle accidents involve head injury. Linear forces were present in only 31% of fatal head injuries, while rotational forces were found to be the primary cause in over 60% of cases. Within the scope of this study experiments were performed using drop tests with accelerometers to measure linear and rotational accelerations of the brain and skull mass associated with different types of impacts. These tests confirmed rotational acceleration to be a primary cause of brain injury in helmeted motorcycle accidents.
While the motorcycle helmet is currently the most effective means of protection for riders, data suggests that motorcycle helmets are only 37-42% effective in preventing fatal injury. By reducing the effects of blunt trauma to the head it is generally believed that risk of brain injury, including concussion, axonal injury and hematoma would also be reduced. However, the mechanisms of head and brain injury are very different. New research shows that these mechanisms are poorly coupled, contrary to previous beliefs.
Summary
Motorcycle helmet expert report that rotational forces acting on the brain are the underlying cause of traumatic brain injuries.
Motorcycle helmets, including those certified under DOT and SNELL standards are designed to mitigate forces associated with linear acceleration.
According to motorcycle helmet expert, helmets are not currently certified under either DOT or SNELL standard against their ability to protect against the angular / rotational forces.
Epidemiologic evidence from the COST-327 report indicates that motorcycle helmets do not provide adequate protection against closed head and brain injuries
New Research
Motorcycle helmet expert Dr. John Lloyd recently published a new study: Biomechanics of Motorcycle Helmets: Protection Against Head and Brain Injury. Testing proves that motorcycle helmets provide inadequate protection against concussion and severe traumatic brain injury associated with even relatively minor head impact
Accidents involving commercial vehicles and truck accident typically involve extensive damage and more severe injuries to vehicle occupants due to the magnitude of forces involved.
Truck Accident Statistics
According to Federal Motor Carrier Safety Administration (FMCSA) data, one person is injured or killed in a truck accident every 10 minutes.
In 2014 there were 213,000 trucking accident resulting in property damage only, 52,000 injury-causing accidents, and 1885 fatal crashes.
About half of all tractor-trailer accidents involve front-end collisions. Back end and side collisions occur in 15 and 12 percent of all crashes, respectively
The top 5 states in which fatal truck accidents occur include Texas, California, Florida, Pennsylvania and Georgia.
Exposure
According to a 2016 AAA report, passenger car drivers spend about 290 hours on the road and travel an average of 10,900 miles each year, with atypical life of a passenger car of 8 years and 150,000 miles. Whereas, tractor-trailer operators may work up to 70 hours per week (55 hours driving time) and often travel 10,000 miles or more in a month. Tractors are typically kept in service for 6 years, during which time they can travel 600,000 miles or more. So, mile-for-mile, a tractor-trailer operator’s exposure is 10-fold that of a passenger car driver.
Who’s at fault?
Nearly 90 percent of all trucking accidents result from human error, rather than mechanical breakdown, equipment failure, bad weather or poor road conditions. Examples of human carelessness or recklessness responsible for causing truck crashes include:
Driving while under the influence of drugs or alcohol
Distracted driving — eating, using cell phones, applying makeup
Driver fatigue
Running red lights, speeding, failing to yield or otherwise violating traffic laws
While some accidents may involve human error on the part of the tractor-trailer operator, trucks and truck drivers are typically held to a higher standard of operation by Federal Laws and Regulations than passenger cars and drivers. Truck drivers need to successfully complete a more extensive driver training program than is required to drive a passenger car. Commercial vehicles are also inspected more thoroughly and on a more frequent basis.
In fact, more than 75% of truck driving accidents are caused by the driver of the passenger vehicle.
Truck Accident Expert
Dr. Lloyd has served as an expert for both defense and plaintiff’s counsel on a number of cases nationwide involving trucking accidents. Dr. Lloyd is uniquely qualified in that he is certified in accident reconstruction, is an internationally-recognized expert in injury biomechanics and can also address the unique human factors issues that affect tractor-trailer operators, such as visual perception and perceived reaction time.
Please call Dr. Lloyd at 813-624-8986 or email DrJohnLloyd@Tampabay.RR.com to discuss how he can be of assistance with your case.
Motorcycle collision analysis is a highly specialized discipline in which Dr. Lloyd is eminently qualified as a motorcycle accident expert. In addition to holding a PhD in Ergonomics (Human Factors), with a specialization in Biomechanics, John has more that 20 years and 200,000 miles of experience riding motorcycles. Dr. Lloyd has completed numerous advanced programs, including Motorcycle Safety Foundation (MSF), Experienced Rider Course and Total Rider Tech Advanced training.
Motorcycle Helmets and Brain Injury
To consider whether a motorcycle helmet might reduce the risk of brain trauma in a motorcycle accident it is first important to understand the two primary mechanisms associated with traumatic brain injury – impact loading and impulse loading.
Impact loading involves a direct blow transmitted primarily through the center of mass of the head, resulting in extracranial focal injuries, such as contusions, lacerations and external hematomas, as well as skull fractures. Shock waves from blunt force trauma may also cause underlying focal brain injuries, such as cerebral contusions, subarachnoid hematomas and intracerebral hemorrhages. Whereas, impulse or inertial loading caused by sudden movement of the brain relative to the skull, produces cerebral concussion. Inertial loading at the surface of the brain can cause subdural hemorrhage due to bridging vein rupture, whereas if affecting the neural structures deeper within the brain can produce diffuse axonal injury (DAI).
Holbourn was the first to cite angular / rotational acceleration as an important mechanism in brain injury. Gennarelli, Thibault, and colleagues, in a series of studies using live primates and physical models investigated the role of rotational acceleration in brain injury. They concluded that angular acceleration contributes more than linear acceleration to brain injuries, including concussion, axonal injury, and subdural hematoma.
Motorcycle Helmet Testing
Traditional testing of motorcycle helmets focuses on reducing the effect of linear impact forces by dropping them from a given height onto an anvil and measuring the resultant peak linear acceleration. According to the Federal Motor Vehicle Safety Standard (FMVSS) 218, commonly known as the DOT helmet standard, the test involves dropping a motorcycle helmet onto a flat steel and hemispherical anvil at an impact velocity of 6.0 m/s (13.4mph). In general, if peak linear acceleration is less than 400g, the helmet is considered acceptable. Current motorcycle helmet testing standards do not incorporate measures of angular acceleration and therefore do not address whether any helmets can provide adequate protection against catastrophic brain injuries, such as concussion, axonal injury and subdural hematoma.
In 1995, the European Commission Directorate General for Energy and Transport initiated a Cooperative Scientific and Technical Research (COST) program to investigate Motorcycle Safety Helmets. Several agencies from Finland, the United Kingdom, France and Germany participated in this study, which compiled and analyzed data from 4,700 motorcycle fatalities in Europe, each year. The COST report documents that 75% of all fatal motorcycle accidents involve head injury. Linear forces were present in only 31% of fatal head injuries, while rotational forces were found to be the primary cause in over 60% of cases. Within the scope of this study experiments were performed using drop tests with accelerometers to measure linear and rotational accelerations of the brain and skull mass associated with different types of impacts. These tests confirmed rotational acceleration to be a primary cause of brain injury in helmeted motorcycle accidents.
Rotational forces acting on the brain are the underlying cause of traumatic brain injuries.
Motorcycle helmets, including those certified under DOT and SNELL standards are designed to mitigate forces associated with linear acceleration.
Motorcycle helmets are not currently certified under either DOT or SNELL standard against their ability to protect against the angular / rotational forces.
Epidemiologic evidence from the COST-327 report indicates that motorcycle helmets do not provide adequate protection against closed head and brain injuries
Human Factors of Motorcycle Accidents
Human factors in vehicle collisions include all factors related to drivers and other road users that may contribute to a collision. Examples include driver behavior, visual and auditory acuity, decision-making ability, and reaction speed. A 1985 report based on British and American crash data found driver error, intoxication and other human factors contribute wholly or partly to about 93% of crashes.
Motorcycle Inspection
Motorcycle accident analysis often requires involves a teardown and careful inspection of the machine to investigate for possible contributing factors. Our engineers have a combined 70 years experience with motorcycle mechanics.
A thorough evaluation includes inspection of tires, brakes, suspension setup, electrical components as well as any aftermarket parts.
Impact loading involves a direct blow transmitted primarily through the center of mass of the head, resulting in extracranial focal injuries, such as contusions, lacerations and external hematomas, as well as skull fractures. Shock waves from blunt force trauma may also cause underlying focal brain injuries, such as cerebral contusions, subarachnoid hematomas and intracerebral hemorrhages.
Dr. Lloyd has completed numerous advanced programs, including Motorcycle Safety Foundation (MSF), Experienced Rider Course and Total Rider Tech Advanced training.
