Category Archives: crash reconstruction

Accident Reconstruction

In the United States there are 11 million motor vehicle accidents each year, more than 400,000 of which result in death. The most common injuries resulting from automobile accidents are to the head, brain, neck, and low back. The evaluation of such cases often involves a team of experts, including accident reconstruction, biomechanics and human factors experts.

As an expert witness in biomechanics and human factors as well as a certified accident reconstructionist for motorcycle crashes, automobile accident, and truck collisions, r. John Lloyd is a highly qualified testifying expert witness.

accident reconstruction expert Dr. John Lloyd

Accident Reconstruction

First the accident reconstructionist evaluates the physical evidence from a crash scene, including skid marks, gouges and other roadway markings, along with crush information from the vehicles along with their final rest positions. This evidence is used to calculate the change in velocity of the subject vehicles. 

Biomechanical Analysis

lloyd accident reconstruction biomechanica modelingThe complete anatomy of the crash (pre and post impact vehicle speeds, whether or not seat belts were worn, faulty airbags, etc.) is conveyed to the biomechanics expert.

Biomechanists use this information to determine occupant kinematics (motion of the vehicle occupants in response to the impact), kinetics (forces acting on various body parts as a result of the collision) and injury mechanisms. This can include the impact to the head and forces transmitted to the brain, blunt trauma to the low back, and shear forces to the cervical vertebrae. Findings are used to determine whether impact locations and forces provide a causal explanation for claimed injuries. Hence the biomechanist can provide rationale as to whom was at fault for the sustained injuries.

As an expert witness in biomechanics and human factors as well as a certified accident reconstructionist for motorcycle crashes, automobile accidents, truck collisions, in addition to bicycle and pedestrian accidents, Dr. John Lloyd is highly valued expert for the evaluation of motor vehicle crashes.

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.

Crash Data (EDR) Retrieval

Crash data retrieval (EDR) is a tool used by accident reconstructionists to download pre and post collision information from vehicles to determine driver behavior, impact severity and the cause of the crash.

Much like an airplane, almost all vehicles in the United States are equipped with a ‘black box’. In the event of an impact critical information about the crash as well as pre-crash information is recorded and stored in this black box, also known as an event data recorder (EDR). The process of obtaining this data is known as crash data retrieval.

It is a common misunderstanding that EDR data is only temporarily saved in the vehicle’s ‘black box’ and is erased after a short period of time. In the event of an airbag deployment, EDR data is almost always recorded and permanently stored. This data is never erased. Whereas, in a non-deployment event (i.e. airbags did not go off), if the event meets the manufacturer’s propriety algorithms to trigger recording, that data is saved, but can be overwritten if the vehicle is involved in subsequent collisions.

Motor vehicle crash data retrieval

crash data download from vehicle event data recorder

This information of vital importance when investigating a crash includes:

  • Speed
  • Change in Velocity (Delta-v)
  • Acceleration / Deceleration 
  • Braking 
  • Pre-crash Steering Inputs/ Angle
  • Seatbelt Usage and airbag deployment

crash data retrieval toolSpecialized equipment is required to access the EDR.

Unfortunately, law enforcement investigating a crash typically only retrieve the information from the Crash Data Recorder in the event of a traffic homicide. Hence, it is up to the accident reconstruction experts to download this information from the vehicles.

EDR data can help an accident reconstructionist to determine:

  1. pre-crash driver behavior
  2. crash severity
  3. who was at fault

Combined with his biomechanical expertise, Dr. Lloyd can use the information from the EDR to determine:

  1. occupant kinematics (motion in response to crash)
  2. whether injuries are consistent with crash severity

Solo Motorcycle Crashes

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:

  1. Riding too fast
  2. 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.

solo motorcycle crash - efficient braking

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.

solo motorcycle crash - rear brake skid

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.

solo motorcycle crash - 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.