Motorcycle helmet expert Dr. John Lloyd has served attorneys nationwide for 25+ years in biomechanics, human factors, helmet testing and motorcycle accident expert
Dr. Lloyd is a distinguished authority in motorcycle accident reconstruction and human factors analysis, with decades of experience. His understanding of the unique dynamics involved in motorcycle crashes sets him apart as a true specialist in the field.
Dr. Lloyd spent his career as a senior researcher at the VA Hospital in Tampa, FL, serving as Director of the Biomechanics Research Laboratory and Director of the Traumatic Brain Injury Research Laboratory. In addition he held a courtesy faculty appointment as Assistant Professor in the University of South Florida College of Engineering from 2002-2022, and is currently the Research Director of BRAINS, Inc.
To date, Dr. Lloyd’s work has been published in six book chapters and 33 peer-reviewed journals, as well as presented at more than 100 national and international conferences (see curriculum vitae).
Comprehensive Approach
Dr. Lloyd goes beyond the obvious and delves deep into the technical intricacies of each case. As a multi-disciplinary expert he combines, accident reconstruction, biomechanics and human factors to provide a holistic view of the accident, ensuring no detail goes unanalyzed.
Accurate Motorcycle Crash Reconstructions
Using state-of-the-science reconstruction tools and real world data, Dr. Lloyd meticulously creates 3D accident reconstructions with unparalleled accuracy. This empowers him to provide precise insights into the sequence of events leading up to the incident.
Human Factors Insight
Understanding the role of human behavior is crucial in accident analysis. Dr. Lloyd’s human factors expertise allows him to investigate the cognitive factors affecting both motorcycle riders and automobile drivers, offering invaluable insights into decision-making processes.
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To date, Dr. Lloyd has provided expert witness Deposition and Trial Testimony in more than 160 civil and criminal cases. His expertise in motorcycle crashes, motorcycle riding and operation, helmet protection, biomechanics and human factors has been recognized by courts across the United States and Internationally. The analysis methods that Dr. Lloyd utilizes are published in peer-reviewed scientific journals.
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The following is a peer-reviewed article on Motorcycle Accident Reconstruction, which was originally published in the Journal of Forensic Biomechanics in January 2016.
Corresponding author: John D Lloyd, Research Director, BRAINS, Inc., 32824 Michigan Avenue San Antonio, Florida, 33576, USA, Tel: 813-624-8986; Fax: 352-588-0688; E-mail: drjohnlloyd@tampabay.rr.com
Abstract
In a motorcycle accident, the motorcycle and rider typically become independent, each following their own path to final rest. Consequently, the biomechanical analysis of a motorcycle accident reconstruction is complex. A biomechanical model to assess rider kinematics associated with motorcycle accidents is presented, which may be important to forensic scientists involved in the analysis of such events. This model can also be applied to other activities, including cycling, equestrian sports, skiing, skating, running, etc.
In a motorcycle accident reconstruction, it is first important to understand the mechanisms by which a rider may be ejected from their motorcycle and how drag factors affect the motorcycle and rider independently. Next we determine rider trajectory, taking into consideration rider anthropometry and posture, results from which are used to derive impact velocity as a function of linear and angular components. A case study is presented, demonstrating how the presented model can be applied to a collision involving a single motorcycle.
Introduction to Motorcycle Accident Reconstruction
Motorcycles are a luxury in the developed world, where they are used mostly for recreation. Whereas in developing countries, motorcycles are required for utilitarian purposes due to lower prices and greater fuel economy. It is estimated that in 2016 there will be more than 134 million motorcycles worldwide [1], 60-80% of which are in the Asia Pacific and Southern and Eastern Asia regions. In 2011 there were more than 8.2 million registered motorcycles in the United States [2], representing 3% of all US registered vehicles, with California, Florida and Texas leading the number of motorcycles per state [3].
3.1. Epidemiology of motorcycle accidents
In the United States motorcyclists travelled 18.5 billion miles in 2011, which represents only 0.6% of total vehicle miles travelled, yet motorcyclists accounted for 14% (4,612) of traffic fatalities and 4% (81,000) of all occupant injuries [2]. According to the U.S. National Highway Traffic Safety Administration (NHTSA), when compared with automobiles, per vehicle mile traveled, motorcyclists’ risk of a fatal crash is 35 times greater than that of a car occupant [4].
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 [5] showed that failure of motorists to detect and recognize motorcycles in traffic is the prevailing 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 of the Hurt study indicate that severity of motorcyclist injury increase with speed, alcohol consumption, motorcycle size and speed.
The MAIDS study (Motorcycle Accidents In Depth Study) [6] is the most recent epidemiologic study of accidents involving motorcycles, scooters and mopeds, which was conducted in 1999 across five European countries to investigate motorcycle accident exposure data. 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 the United States alone, it is estimated that the total direct costs associated with motorcycle crashes in 2010 was approximately $16 billion. However, the US Government Accountability Office (GAO) predicts that full costs of motorcycle crashes are likely considerably higher because some difficult-to-measure costs, such as longer-term medical costs, are not included [7].
Biomechanical Model
A new model is presented for the purpose of investigating motorcycle accident reconstruction biomechanics involving a lone motorcycle, which accounts for 25% of all motorcycle-related accidents according to the Hurt report [5]. This model is unique in that it incorporates measures of rider anthropometry (body measurements) and riding posture, which have a direct effect on trajectory and overall height of the vertical component of the impact.
The model presented herein may be applied not only to motorcycle accidents, but also to a wide range of activities, including cycling, equestrian sports, skiing, skating, running, etc.
Methods
It is first important to understand the mechanisms by which a rider may be ejected from their motorcycle and how drag factors affect the motorcycle and rider independently. Next we determine rider trajectory, results from which are used to derive impact velocity as a function of linear and angular components. Finally, characteristics of the impact surface are considered with respect to impact accelerations.
5.1. Rider ejection
There are a number of ways that a rider can be ejected from the bike in a lone motorcycle accident. Two common ways of ejection are the lowside (Figure 1A) and highside (Figure 1B) crash. A rider may also be ejected over the handlebars (Figure 1C).
Figure 1 – Rider Ejected from Motorcycle
The lowsider or lowside is a type of motorcycle crash usually occurring in a turn (Figure 1A). A lowside crash is caused when either the front or rear wheel slides out as a result of either too much braking in a corner, too much acceleration through or out of a corner, or too much speed carried into or through a corner for the available traction. A lowside crash may also be caused by unexpected slippery or loose material (such as oil, water, dirt or gravel) on the road surface.
A highsider or highside is a type of motorcycle accident characterized by sudden and violent rotation of the motorcycle about its longitudinal axis. This generally happens when the rear wheel loses traction, skids, and then suddenly regains traction, creating a large torque, ejecting the rider off the side of the motorcycle, oftentimes head-first (Figure 1B).
Highside and lowside accidents differ as follows: during a lowside the rear wheel slips laterally and continuously until the motorcycle falls onto the side facing the inside of the corner.Whereas during a highside crash the rear wheel slips laterally before suddenly regaining traction and flipping the motorcycle toward the outside of the corner (the higher side of the motorcycle). Highsides happen quickly and are very violent consequently injuries tend to be more severe in a high side crash, compared to a lowside crash.
Endo, short for “end over end,” occurs when the front end of a motorcycle stays fixed while the rear rotates up into the air, causing a rider to fly over the handlebars (Figure 1C).
5.2. Drag factors
Drag factors for motorcycles have been established based on motorcycle accident reconstruction and typically range from 0.2-1.0 [8], where 0.25 represents a motorcycle with a fairing [9], such as a sport motorcycle. Sport and sport touring motorcycles will likely slide further than a cruiser-style motorcycle, which have more external components that resist sliding, for which a drag factor of 0.5 is commonly adopted Table 1, below, presents drag factors for street motorcycles sliding on typical road surfaces [10-13].
Table 1: Drag Factors for Sliding Motorcycles
Drag factors for the rider are typically higher than those for motorcycles sliding on a dry asphalt or concrete roadway. An extensive series of motorcycle accident reconstruction tests were carried out by the West Midlands Police in the United Kingdom in which they calculated the drag factor value of a crash-test dummy sliding across an airfield surface. The resulting coefficient was found to vary between 0.57 and 0.85 for normal clothing [14].With similar drag factors for dry and wet roadway conditions [15]. For the purpose of accident reconstruction, a drag factor of 0.7 for a clothed individual sliding on a roadway is generally accepted.
Evidence from final rest positions of the motorcycle and rider can be used to establish whether the rider was involved in a lowside or highside motorcycle ejection. In a lowside crash the motorcycle will tend to slide further than the rider. Whereas in a highside crash, the rider is ejected from the motorcycle, traveling additional distance over ground in a similar direction to the motorcycle, prior to making contact with the ground and initiating the slide. Hence, in a highside crash, the final rest position of the rider may be beyond the final rest position of the motorcycle. Furthermore, in higher-energy ejection crashes the rider is more likely to both slide and tumble, resulting in a longer travel distance from location of ejection from the motorcycle, as well as additional injuries as evidenced by fractures, lacerations and contusions to various regions of the body.
5.3. Rider anthropometry
Anthropometry is the study of human body measurements. Rider anthropometry will directly affect fall height, since head center of mass (HCOM) and overall center of mass (RCOM) varies between individuals.
In a lowside crash, seated height of the center of mass (HCOM) of the rider’s head approximates vertical fall height. Whereas in a highside crash vertical fall height is a function of seated head CoM height (HCOM), plus additional height gained based on trajectory of the rider calculated with reference to overall center of mass of the rider (RCOM) (Figure 2).
Figure 2 – Fall Height Associated with Low side and High side Accidents
5.4. Rider center of mass
Rider center of mass height (RCOM) is located anatomically with respect to the second sacral vertebra (S2), which can be visually estimated as approximate in height to the omphalion (navel), and is measured vertically with respect to the road surface. The preferred method for determining RCOM is to measure seated height of the rider on the subject motorcycle (Figure 3). If the rider is not available due to injury or fatality, then an exemplar same-gender person of similar height and weight may be used. If the subject motorcycle is not available due to extent of damage, then an exemplar motorcycle should be obtained. With the motorcycle supported perpendicular to the road by an assistant (not on side stand or center stand), and rider’s hands on the handlebar grips and feet on the foot pegs, measure the vertical height from the ground to the motorcycle seat at the location of the ischial tuberosities (base of the pelvic bones at the seat surface). An anthropometer and spirit level should ideally be used for accuracy and measurements recorded in millimeters to maximize precision.
Figure 3 – Rider anthropometry
As an alternative method, rider seated height can be calculated by sourcing motorcycle seat height, from manufacturer specifications, from which a correction factor for suspension compression under mass of the rider is subtracted. Suspension compression, also known as sag, will vary by motorcycle type and mass of the rider. A general rule of thumb is that the front sag should be about 30-35% of travel, while the rear should be at about 25%, which equates to 30-40 mm at the front and 25-35 mm at the rear for most bikes [16]. Therefore, a reasonable correction factor for suspension sag is 30-35 mm.
For both methods, an adjustment must be added to the compressed seat height to determine RCOM. According to Pheasant [17], seated RCOM is equal to seat height plus 10% of total stature (standing height). This factor calculation is identical for both males and females (Table 2).
Table 2: Anthropometric Data
5.5. Head center of mass
Head center of mass (HCOM) height can also be measured directly using the method described earlier, with the rider seated on the subject motorcycle in the correct riding position. An anthropometer is used to measure the vertical height from the ground. If the rider and/or subject motorcycle is unavailable, a substitute individual of similar height and weight and exemplar motorcycle may be used. The canthus (outer corner of the eye) is used as an anatomical landmark reference, equal in height to the center of mass of the head (Figure 3).
Alternatively, seated head center of mass (HCOM) can be calculated as a function of stature (standing height). Utilizing data from the 1988 Anthropometric Survey of U.S. Personnel [18], HCOM is derived by multiplying stature by 45.2%. Similar to the RCOM calculation, HCOM must be corrected for posture by multiplying HCOM by the cosine of seated back angle (β), measured with respect to the vertical axis.
5.6. Trajectory of the rider
The trajectory is the path that a rider is thrown or vaulted under the action of gravity, neglecting all other forces, such as friction from air resistance, without additional propulsion (Figure 4) and is defined by Equation 1.
Equation 1 – Trajectory of the ejected rider (y):
Figure 4 – Trajectory of an Ejected Rider
The following standard mathematical formulae are used to determine specific components of trajectory that are pertinent to the kinematic analysis of a rider ejected from a motorcycle.
5.7. Distance travelled
In a motorcycle accident reconstruction it may be possible to establish the actual distance of ejected travel of the rider, based upon location of ejection, typically between the end of any tire skid marks and start of gouge marks on the roadway, and location of bodily impact with the ground, identified by helmet paint transfer and/or identification of clothing fibers or body tissue on the roadway consistent with the rider. If the speed of the motorcycle at ejection (νejection) is also known, then the distance travelled (d) can be computed using the formula below, taking into account any correction factors for relative change in road height from location of ejection to impact.
Equation 2 – Horizontal distance traveled (d):
However, the location of bodily impact is often difficult to identify, in which case reasonable assumptions may be made, including utilization of an estimated ejection angle (θ).
5.8. Maximum height
One of the most critical factors for determination of total impact velocity in a motorcycle accident reconstruction is the maximum height attained by an ejected rider, which is calculated according to
Equation 3 – Maximum height (h):
5.9. Ejection angle
The ejection angle (θ) is the angle at which a rider must be launched in order to travel a certain distance, given the initial velocity. Oftentimes, based on the final rest positions of the motorcycle and rider and in consideration of appropriate drag factors, it is possible to approximate rider ejection velocity. Air resistance is considered negligible, therefore angle and velocity at ejection are considered equal to the angle and velocity at impact.
Equation 4 – Ejection angle (θ):
5.10. Rider impact velocity
Total impact velocity is derived on the basis of its vertical, angular and travel velocity components.
5.11. Linear vertical impact velocity
Vertical impact velocity is computed as a function of seated head height, plus any additional height gained due to rider ejection from the motorcycle. The potential energy (P.E.) at any point will depend on the mass (m) at that point and its distance above the ground (h), multiplied by the gravitational acceleration constant (g) (Figure 5).
Figure 5 – Potential Energy of a Motorcyclist
The potential energy of the entire system is the integral of the energies of each finite mass element of the motorcycle plus rider over its height: . For simplification, we assume that the mass is evenly distributed over the system. Hence, P.E=m g h.
In physics, the law of conservation of energy governs that energy can neither be created nor destroyed, Potential Energy (P.E.) at the start of a fall must be equal to the Kinetic Energy (K.E.) at the end of the fall, which is expressed as the product of one half mass (½m) and impact velocity squared (v2). Therefore P.E. = K.E. = ½ mv2, Solving for linear impact velocity gives Equation 5:
Equation 5 – Linear impact velocity:
5.12. Angular vertical impact velocity
In real-world scenarios a falling rider will not follow a purely linear path [19], especially when coupled to a rigid body such as a motorcycle, hence angular velocity will also be generated (Figure 6).
Figure 6 – Falling Motorcyclist
If a motorcyclist falls from a vertical to a horizontal position, we can assume that Potential Energy (P.E.) is converted to rotation: 1/2m g h = ½ I ω2 where is the Moment of inertia, defined as the ratio of the angular momentum (L) of a system to its angular velocity (ω) around an axis: I=L/w which may also be expressed in terms of its mass (m) and its distance (r) from the pivot point as: I=mr2. Since r = h, the equation can be rewritten: mgh=1/2mh2w2. Instantaneous angular velocity at impact can be expressed in terms of linear components: ν = ω h, thus mgh=1/2mv2 which yields Equation 6:
Equation 6 – Instantaneous velocity due to angular rotation upon impact:Hence total impact velocity is the sum of its linear and angular components.
Therefore, the sum of impact velocity due to linear and angular components is greater than impact velocity due to linear components only and is expressed as:
As previously stated, air resistance during a short fall is considered negligible, therefore angle and velocity at ejection (α, νejection) is considered equal to the angle and velocity at impact. Velocity due to ejection can be expressed in terms of its vertical and horizontal components . Assuming that ejection angle is measured with reference to the horizontal axis, then:
Equation 8a – Vertical ejection velocity:
, and Equation 8b – Horizontal ejection velocity:
5.14. Impact velocity vector
The impact velocity vector has both vertical and horizontal components. The total vertical velocity is the sum of the linear and angular velocity components, plus the vertical components of velocity due to ejection. The total horizontal velocity will equal the horizontal component of velocity due to ejection. The magnitude of the impact velocity vector will be the square root of the sum of its vertical and horizontal components, hence:
Equation 9 – Impact velocity vector:
and the effective angle of the impact velocity vector relative to the vertical axis is determined as:
Equation 10: Effective impact angle:
5.15. Impact acceleration
In a motorcycle accident reconstruction, impact acceleration is determined as a function of rate of change of impact velocity over time (t): , where the duration of the impact will be directly affected by the stopping distance of the impacted material. Roadside materials, such as grass or dirt inherently have larger stopping distances than typical roadway materials, such as asphalt or concrete. Hence, the impact accelerations experienced by a rider landing on a grassy area will be considerably less than if they impacted the roadway.
Motorcycle Accident Reconstruction Case Study
A cruiser motorcycle was traveling along a divided highway, approaching an intersection, when a slow-moving automobile made an abrupt unanticipated lane change immediately in front of the motorcycle. The rider applied the brakes, locking up the rear wheel, causing the motorcycle to skid. The motorcyclist swerved in an attempt to avoid contact with the automobile. The left motorcycle footplate struck the rear corner of the automobile at an impact speed of 7.2 m/s (16 mph), causing the motorcycle to rotate violently about its long axis until the tires gained traction and the rider was thrown from the motorcycle. The final resting position of the rider was 4.6 m (15 ft.) past the final resting position of the motorcycle, to which the rider slid approximately 3.7 m (12 ft.) after being vaulted approximately 6.1 m (20 ft.) from the motorcycle (Figure 7).
Figure 7 – Case study: Automobile Avoidance Collision
The rider center of mass was calculated based on anthropometric derivation from known standing height of 1.7 m (5’8”) and manufacturer’s seat height specification of 0.7 m (27.5”), from which a suspension compression factor of 30 mm (1.2”) was subtracted. Head center of mass was calculated to be 1.45 m (57”). Given a minimal back angle correction factor, based on rider position on a cruiser motorcycle, the corrected HCOM was 1.4 m (55”).
Based on the distance that the rider was thrown and given an ejection velocity of 16 mph an ejection angle of 42 degrees was computed in this motorcycle accident reconstruction. Hence, it was determined that the rider gained an additional height of 1.2 m (39”) due to ejection, which is added to the rider head center of mass height of 1.4 m (51”), for a total fall height of 2.6 m (8’6”). Using equation 7, an impact velocity of 8.0 m/s (18 mph) was calculated for the rotating fall. Since impact velocity and angle is assumed identical to ejected velocity and angle, travel velocity expressed in terms of its vertical and horizontal components, are 4.8 m/s (10.7 mph) and 5.3 m/s (11.9 mph), respectively. Therefore, the total impact velocity vertical and horizontal components are (8.0 + 4.8) = 12.8 m/s (28.7 mph) and 5.3 m/s (11.9 mph), respectively, with an effective impact angle of 22 degrees relative to the vertical axis.
The helmeted motorcyclist impacted an asphalt roadway, head first. Given the inherently very short stopping distance of such materials, the duration over which the impact velocity was experienced was very short, resulting in high impact accelerations, which produced life-threatening traumatic brain injuries.
The results computed by our motorcycle accident reconstruction model were validated by and corroborated based upon physical evidence from the accident scene as well as the physical evidence of the injuries sustained by the rider.
Conclusions
The motorcycle accident reconstruction model presented herein has been successfully applied to a typical case study involving a single motorcycle collision. Measures of rider anthropometry were incorporated into the model. In the presented motorcycle accident reconstruction case study, the rider’s stature was smaller than that of an average male and seat height was lower than most stock motorcycles. Had average male stature and average motorcycle seat height been utilized, such assumptions would have over-estimated total fall height, thereby producing a calculated vertical impact velocity greater than was actually realized. In certain circumstances, specifically where ejection angle approaches 45 degrees, a simplified model without correction for rider anthropometry and rider posture might produce results that are in disagreement with physical evidence from the accident scene. However, this improved model is not without limitations. Specifically, if a rider were leaning the motorcycle considerably at the time of loss of control, such as when cornering, the initial vertical component (yo) would be reduced. This lean angle could be estimated given the radius of the corner and if the initial speed of the motorcycle can be computed. Overall, the validation of our new motorcycle accident reconstruction model is demonstrated in its application to the motorcycle accident reconstruction case study, which is in agreement with physical evidence from the accident scene.
8. References
[1] RnR Market Research (2014) Market Research Reports Press Release: Global motorcycles market demand to rise 7.2% annually to 2016. Published July 31.
[2] National Safety Council (2013) Injury Facts – 2013 Edition. Itasca, IL..
[4] NHTSA’s National Center for Statistics and Analysis (2007) Motorcycles Traffic Safety Fact Sheet (DOT-HS-810-990), 1200 New Jersey Avenue SE, Washington, DC 20590: National Highway Traffic Safety Administration.
[5] Hurt HH, Ouellet JV, Thom DR (1981) Motorcycle Accident Cause Factors and Identification of Countermeasures. Volume 1: Technical Report. University of Southern California Traffic Safety Center, Los Angeles, CA..
[6] ACEM (2000) MAIDS (Motorcycle Accidents In Depth Study): In-depth investigations of accidents involving powered two wheelers – Final Report. European Association of Motorcycle Manufacturers, Brussels..
[7] U.S. Government Accountability Office (2012) Motorcycle Safety: Increasing Federal Funding Flexibility and Identifying Research Priorities Would Help Support States’ Safety Efforts. Report number GAO-13-42.
[9] Medwell C, McCarthy J, Shanahan M (1997) Motorcycle Slide to Stop Tests. SAE Technical Paper 970963., SP-1237 Accident Reconstruction and Animation VII, Warrendale, PA
[10] Southwestern Association of Technical Accident Investigators (1984) Motorcycle Drag Factor Tests. Phoenix, AZ.
[11] Day TD, Smith JR (1984) Friction Factor for Motorcycles Sliding on Various Surfaces. SAE paper 840250. Society of Automotive Engineers, Warrendale, PA.
[12] Iowa State Patrol (1985) Motorcycle Test Skidding on its Side, Traffic Investigation Spring Seminar. Johnston, IA..
[13] Royal Canadian Mounted Police (1984) Motorcycle Testing. Coquitlam, BC, Canada.
[14] Hague DJ (2001) Calculation of Impact Speed from Pedestrian Slide Distance. Proceedings of The Institute of Traffic Accident Investigators International Conference
[15] Searle JA, Searle A (1983) The Trajectories of Pedestrians, Motorcycles, Motorcyclists, etc., Following a Road Accident. SAE paper 831622.. Society of Automotive Engineers, Warrendale, PA.
[16] Thede P, Parks L (2010) Race Tech’s Motorcycle Suspension Bible. Motorbooks International publisher, UK. Cd s.
[17] Pheasant, S. (1998) Bodyspace. Taylor and Francis, London.
[18] Gordon CC, Churchill T, Caluser CE, Brandtmiller CB, McConville JT et al. (1989).1988 Anthropometric Survey of US Army Personnel. US Army Technical Report TR-89/044. Natick, MA.
[19] Barnett, RL (1995) The drunk, the child and the soldier – my how they fall. Triodyne Inc. Safety Bulletin. ISSN 1081-4140. Vol 2 (2).
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.
A better question might be “Can Helmets Prevent Brain Injury?” Same answer – No.
It is not currently possible to develop a helmet that can protect all persons under all foreseen and unforeseen circumstances. But, given current medical understanding of head and brain injuries as well as 21st Century advanced materials, it is certainly possible to protect most people from life-threattening brain injuries under foreseen circumstances.
Helmets are actually intended to protect against blunt trauma injuries to the head. They are not specifically designed to prevent brain injuries.
The mechanisms which cause head and brain injuries are quite different. Forces associated with linear accelerations are responsible for visible injuries, such as lacerations, contusions and skull fracture. Whereas, brain injuries, including concussions, axonal injury and subdural hematoma are caused by forces associated with angular / rotational accelerations. When the head impacts a surface, the skull may come to an abrupt stop, but inertia acting on the brain will cause it to continue to move This inertia strains the nerves and blood vessels of the brain, causing injuries. The type of injury is dependent on the magnitude of this strain and the time duration over which it acts on the brain.
Helmets may indeed reduce the rotational forces acting on the brain. But since helmets are not currently certified according to their ability to protect against brain injury the level of protection is not standardized. Hence, it is possible to sustain catastrophic brain injuries, even while wearing a helmet.
I have performed extensive biomechanical testing of helmets for various applications, including military, motorcycle, football, skiing / snowboarding and cycling. My testing involves measurement of both linear and angular accelerations, thereby characterizing helmets in terms of their ability to protect against head and brain injuries. Results vary substantially between manufacturers that offer helmets for particular applications and between applications. Based on my testing to date, I can report that certain football helmets seem to outperform helmets in other categories in terms of their ability to protect against head and brain injuries.
Much research has been conducted to understand and quantify biomechanical thresholds for various head and brain injuries, including skull fractures, concussions, axonal injury (damage to nerve fibers in the brain) and subdural hematomas (bleeding in the brain). Why then don’t all helmet manufacturers strive to provide necessary protection?
There are certain intrinsic or personal factors that might increase one’s risk of head and brain injury, but for the rest of us, why do helmets provide inadequate protection against life-threatening head and brain injuries during reasonable or foreseen use?
One example of this is the life-threatening brain injury which former Formula One superstar, Michael Schumaker sustained when he fell while skiing and impacted a rock. It has been reported that Mr. Schumaker was only skiing at about 13mph when he fell and the likelihood of impacting a fixed object while skiing, such as a tree or rock is certainly not unforeseen. So why did his helmet fail to provide necessary protection?
Advanced materials certainly exist to provide required protection for normal persons, including Mr. Schumaker and many other unfortunate victims, under normal or foreseen circumstances. As end-users, we must demand that regulatory organizations require helmet manufacturers meet standards that protect persons who are not otherwise at heightened risk from head and brain injuries due to foreseen circumstances.
Motorcycle accident victims account for more than 340,000 fatalities annually, with the United States ranking 8th highest worldwide in the number of motorcycle accident deaths. 75% of all fatal motorcycle accidents involve brain injury, with rotational forces acting on the brain the primary cause of mortality. Current motorcycle helmets are effective at reducing head injuries associated with blunt impact. However, the mechanism of traumatic brain injury is biomechanically very different.
Samples of 9 motorcycle helmet models, representing full-face, three-quarter and shorty designs were evaluated. Helmets, fitted to an instrumented Hybrid III head and neck, were dropped at 13 mph in accordance with DOT motorcycle helmet testing standards.
Results show that, on average, there is a 67% risk of concussion and a 10% probability of severe or fatal brain injury associated with a relatively minor 13mph helmeted head impact.
In conclusion, motorcycle helmets provide inadequate protection against concussion and severe traumatic brain injury associated with even relatively minor head impact
John Lloyd of BRAINS, Inc. announced today that football head injuries and concussions can be reduced up to 50 percent with their new helmet safety breakthrough.
San Antonio, FL – Dr.John Lloyd PhD of BRAINS, Inc. announced their latest breakthrough in football helmet safety today. The unique new helmet technology promises to provide up to 50 percent more protection against football head injuries and concussions. The technology has wide application and can be used in every kind of helmet from baby helmets to military helmets, and for all athletes at risk of concussion and head injuries such as football players, cyclists, skiers, snowboarders, skateboarders, hockey players, baseball players, lacrosse players, boxers, soccer players, equestrian / horse-riding sports, such as polo and horse racing, as well as motorcycle and race car drivers.
Recent medical research documents found that concussions and cumulative head impacts can lead to lifelong neurological consequences such as chronic traumatic encephalopathy, a degenerative brain disease known as CTE and early Alzheimer’s.
The U.S. Centers for Disease Control and Prevention, estimates 1.6 – 3.8 million sport-related brain injuries annually in the United States. Of these 300,000 are attributed to youth football players, some of whom die from their injuries every year – a tragedy difficult for their mothers and families to recover from.
The severity of the issue touching both the nation’s youth and professional athletes has led to thousands of lawsuits and Congressional Hearings. Growing concern has spread to the White House where President Obama recently spoke at the Healthy Kids and Safe Sports Concussion Summit.
The BRAINS, Inc. research team, led by renowned brain injury expert, Dr. John Lloyd, has worked for years on their project to help make sports safer. A controversial subject, some opponents have stated that concussion prevention is impossible. Dedicated to saving lives and preserving brain health, Dr. Lloyd and team persevered with their work leading to this new innovation. “Our results show that forces associated with concussion and brain injury are reduced up to 50% compared to similar testing with a leading football helmet,” said Dr. John Lloyd, Research Director.
“The patent-pending matrix of non-Newtonian materials will not only benefit football, but can be utilized in all sports helmets as well as military, motorcycle and even baby helmets to improve protection and dramatically reduce the risk of brain injuries,” reported Dr. Lloyd.
The materials are inexpensive, and produce a helmet that is considerably lighter and more comfortable than a traditional helmet. Two additional applications of this new safety technology include medical flooring especially in hospitals and nursing homes or child play areas , as well as vehicle interiors.
About BRAINS, Inc.
BRAINS, Inc. located in San Antonio, Florida, is a research and development company focused on the biomechanics of brain injuries. The company was founded in 2011 by John D. Lloyd Bio, Ph.D., CPE, CBIS, Board Certified Ergonomist and Certified Brain Injury Specialist. He has also provided expert witness services nationwide for over 20 years in the fields of biomechanics, ergonomics and human factors, specializing in the biomechanics of brain injury, including sport and motorcycle helmet cases, slips and falls, motor vehicle accidents and pediatric head trauma. BRAINS, Inc. is open to licensing with manufacturers to bring this much-needed technology to market for the protection of sports participants and athletes of all ages. For additional information visit : http://drbiomechanics.com/sports-helmet-football-helmets/new-helmet-technology/ or call 813-624-8986.
Motorcycle helmets were originally developed in the early 20th century and, like most helmets, are modeled after military helmets, the purpose of which is to protect against penetrating head injury. The modern motorcycle helmet, with a hard outer shell and rigid expanded polystyrene (EPS) liner was actually introduced over 60 years ago. The outer shell serves as a second skull, dispersing the impact force over a wider surface area, while the inner shell compresses in an attempt to reduce translational forces. A mechanism to mitigate tangential forces is absent. Since the liner fills the entire inner surface of the shell, tangential forces cannot be absorbed and are transmitted directly to the head and brain. Motorcycle helmet standards focus 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.
Motorcycle Helmet Standards
In motorcycle helmet testing, the risk of impact loading injuries, such as skull fractures, can be determined by measuring linear accelerations experienced by a surrogate head form in response to impact. Whereas risk of impulse or inertial loading injuries, such as concussion, axonal injury and subdural hematoma can be quantified by measuring impact-related angular accelerations at the center of mass of a test head form.
Unfortunately, the evolution of motorcycle helmet design is not driven by advances in scientific knowledge, but rather by the need to meet applicable testing standards. In the United States, standards include the federal motor vehicle safety standard (FMVSS) #218, commonly known as the DOT motorcycle helmet testing standards, and Snell M2015, while ECE 22.05 and BSI 6658 were adopted in European countries. Test procedures involve dropping a helmeted head form onto various steel anvils at impact velocities ranging from only 5.0 to 7.75 m/s (11-17 mph). Pass/fail is based on the ability of the helmet to provide protection against forces associated with linear acceleration in response to impact.
Current motorcycle helmet testing standards do not incorporate measures of angular acceleration and therefore fail to assess whether helmets offer protection against catastrophic brain injuries. The omission of this critical measure is reflected epidemiologically in the disproportion of closed head injuries in fatal motorcycle accidents.
Two helmeted motorcyclist were traveling on a rural state road when a tractor-trailer driver failed to see the bikes and made a left turn in front of them to enter a truck stop. The rider in the right track had little time to respond and collided head first into the box trailer. He was pronounced deceased at the scene.
The helmeted motorcyclist was wearing a non-compliant or ‘novelty’ helmet, which did not meet DOT motorcycle helmet standards (FMVSS 218). Opposing counsel claimed that had the biker been wearing a DOT-certified motorcycle helmet he may have survived the impact.
Motorcycle helmet expert, Dr. John Lloyd, was retained to evaluate and compare the protective performance of DOT-certified and novelty motorcycle helmets.
Based on a comprehensive motorcycle accident reconstruction it was determined that the impact speed of the rider was 45 to 50 miles per hour. Motorcycle helmet certification tests typically involve impact speeds of 13-17 miles per hour. Therefore a dedicated apparatus was constructed to generate higher impact speeds. Using a force-balanced twin pendulum apparatus, Dr. Lloyd was able to generate head impact speeds similar to those specific to the subject crash, yet preserve the standard DOT test methodology, thereby avoiding a Daubert challenge.
Eight DOT and non-DOT helmets were purchased for this study. Each was impacted once in the frontal region while fitted to an instrumented crash test dummy head. High speed data and video were acquired for each test.
Results demonstrate that, although the tested DOT-certified motorcycle helmets outperformed the tested novelty helmets, neither would provide adequate protection against head injuries, such as skull fractures, contusions and lacerations, or brain injuries, including hemorrhages or axonal injury in an impact of this magnitude.
Dr. Lloyd’s prior published motorcycle helmet studies demonstrate that while DOT-certified motorcycle helmets can reduce the risk of traumatic head injuries, typical helmets do not afford any protection against acute brain injury.
I am a motorcycle enthusiast and a biomechanics researcher focusing on head and brain injury. Over the years I have performed more than 2600 helmet impact tests. The following are my take-away points for motorcyclists:
Helmets are the best protection we have against head and brain injuries. That said, standard certified motorcycle helmets are only 37-42% effective in preventing fatal head injuries.
Helmets are designed after ancient military helmets to serve as a second skull and thereby protect the head against focal injury.
However, standard motorcycle helmets are not intended to protect against rotational brain injuries.
There are two types of head and brain injuries, which are caused differently:
Translational (linear) forces cause focal injuries including cuts, bruises, and skull fractures.
Tangential forces cause rotational injuries including concussion, brain nerve damage, and brain bleeding.
Translational and tangential forces are generated in every impact
Certified motorcycle helmets do a great job of protecting against focal head injuries.
My research shows that DOT-certified motorcycle helmets reduce the risk and severity of focal injuries by 93 percent.
Novelty (non-certified) helmets do not offer any significant protection against focal injuries.
It is therefore highly recommended that riders wear a certified motorcycle helmet at all times.
Helmets that offer greater coverage, i.e. open-face (3/4) and full-face helmets, provide the best protection against focal injuries. However, the US DOT standard (FMVSS 218)[i] does not require impact testing of the chin bar, therefore there is no certified protection against facial injuries for full-face helmets that are only certified to the DOT standard.
Generally, certified motorcycle helmets do not protect against rotational brain injuries. In fact, on average, a standard certified motorcycle helmet will actually increase the rider’s risk of concussion, nerve damage (axonal injury), and brain bleeding (subdural hemorrhage) by 19 percent, compared to an unhelmeted head impact.
Rotational brain injuries are the cause of fatalities in two-thirds of all helmeted motorcycle deaths.
It has been shown that, in general, larger and heavier helmets increase the risk of rotational brain injuries, including concussion, axonal injury, and brain bleeding because they generate greater impact-related rotational forces on the brain.
So, what can a safety-minded rider do to minimize their risk?
Revised motorcycle helmet standards are starting to look at brain injury risk. The new ECE 22.06 [ii] and Snell M2025[iii] standards now measure the risk of rotational brain injury, though the passing threshold is 23% risk of neurologically devastating or potentially fatal rotation brain injury, at a moderate impact speed of 17.5 mph.
My recommendation is to choose a helmet that meets either the ECE 22.06 or Snell M2025 standard, in addition to whatever standard is mandated in your country.
Choose a lighter, smaller helmet with the desired coverage over a larger, heavier helmet. Not only will this likely provide better protection against rotational brain injuries, but will also generate less wind resistance and be more comfortable on those longer rides.
Consider helmets that incorporate new technologies that are intended to reduce the risk of rotational brain injuries.
Don’t buy a helmet just based on looks, make an informed purchase based on fit and protective performance.
What can motorcycle helmet manufacturer’s do to improve helmet performance?
Current motorcycle helmet designs may be over-engineered to reduce translational forces that cause focal head injuries, resulting in helmets that are larger and heavier, thereby increasing the risk of rotational brain injuries, which are the primary cause of fatality in two-thirds of helmeted motorcycle crashes. Protection against focal injuries is important, but needs to be balanced against increased risk of rotational brain injuries. Manufacturers should evaluate materials that allow the development of smaller and lighter helmets.
A meta-analysis is underway, comparing helmets intended for a variety of activities including motorcycling, skiing, bicycle, off-road, American football, ice hockey and military. Preliminary results suggest that helmets intended for other sports activities may outperform motorcycle helmets at similar impact speeds in terms of protection against both focal head injuries and rotational brain injuries
[i] U.S. Department of Transportation (2013) Federal Motor Carrier Safety Administration Standard No. 218, Motorcycle helmets. Washington, DC.
[ii] United Nations (2021). Uniform Provisions Concerning the Approval of: Protective Helmets, of their Visors and of their Accessories for Drivers and Passengers of Motorcycles and Mopeds. Regulation No. 22-06
[iii] Snell Memorial Foundation. (2024). Standard for Protective Headgear for use with Motorcycles and Other Motorized Vehicles. M2025