Becoming an Expert in Accident Reconstruction

Accident reconstruction utilizes principles of physics and empirical data to analyze the physical, electronic, video, audio, and testimonial evidence from a crash, to determine how and why a crash occurred or to determine whose description of the crash is most accurate. Accident reconstructionists may also analyze how a crash could have been avoided. Crash reconstruction draws together aspects of mathematics, physics, engineering, materials science, and psychology and combines analytical models with empirical test data. Different types of crashes – vehicle-to-vehicle collisions, single vehicle rollover crashes, pedestrian and bicycle crashes, motorcycle crashes, or heavy truck crashes, for instance – produce different types of evidence and call for different analysis methods. Still, the basic philosophical approach of the reconstructionist is the same from crash type to crash type, as are the physical principles that are brought to bear on the analysis.

Technical Competence

Following is a description of the characteristics and knowledge-base of a competent accident reconstructionist. When you achieve this level of expertise, you will be an indispensable part of a team of accident reconstructionists. This level of expertise will not necessarily qualify you to manage projects or to lead a team. This level is, however, an essential baseline to achieve if you aspire to manage projects, manage a team, or to testify.

1. The competent accident reconstructionist has read and mastered the material in the following books:

   • Traffic Crash Reconstruction, Lynn Fricke

   • Fundamentals of Traffic Crash Reconstruction, Daily

   • Vehicle Accident Analysis and Reconstruction Methods, Brach and Brach

2. The competent accident reconstructionist has studied these books in sufficient depth to know that they do not agree on everything and each of them probably contains some errors. They are useful, but not authoritative.

3. The competent accident reconstructionist begins with the end in mind. What questions are you trying to answer? What is the source of these questions (i.e. the client, the type of case)? What do you need to know in order to answer those questions? The competent accident reconstructionist understands what details are not important in answering the relevant questions.

4. The competent accident reconstructionist knows the characteristics and meaning of the many common types of physical evidence. For example:

   • Tire Marks

     1. Skid Mark

     2. Yaw Mark

     3. Striations within tire marks

     4. Crooks in tire marks that define the location of impact

   • Scrapes and Gouges

   • Vehicle Crush

     1. Direct versus induced

     2. Dynamic versus residual

   • Scratches on Vehicle Body Panels

   • Glass and debris deposits

5. The competent accident reconstructionist can integrate the many types of evidence - physical, electronic, video, audio, testimonial - into a coherent and justified accident reconstruction.

6. The competent accident reconstructionist understands and applies the following physical principles for analysis:

   • Conservation of Momentum/Principle of Impulse and Momentum

   • Conservation of Energy/Energy Balance

   • Principle of Work and Energy

7. The competent accident reconstructionist understands that many crash types are split into phases for analysis and confidently identifies these phases in the physical evidence. For example:

   • Pre-impact, impact, and post-impact

   • Yaw, trip, roll

   • Loss of control, capsizing, tumbling

8. The competent accident reconstructionist understands and applies common and widely-accepted analysis techniques for various crash types. For example:

   • Vehicle-to-Vehicle Collisions

     1. Planar Impact Mechanics 

     2. Crush Analysis 

     3. Energy Balance (Conservation of Energy)

        1. Analysis of Post-Impact Vehicle Spin with Braking

        2. Striation Analysis

        3. Tire Modeling

     4. Simulation Software (at least one of the following):

        1. PC-CRASH 

        2. Virtual Crash 

        3. HVE

   • Rollover Crashes

     1. Speed Analysis using Energy Balance (Conservation of Energy)

     2. Analysis by Phases

        1. Yaw Phase

        2. Trip Phase 

        3. Roll Phase

   • Motorcycle Crashes

     1. Car Crush and Motorcycle Wheelbase Reduction

     2. Post-Impact Translation and Rotation of the Struck Vehicle

     3. Slide to Stop

     4. Incorporating EDR Data

   • Heavy Truck Crashes

     1. Brake force calculations

9. The competent accident reconstructionist understands the assumptions and limitations of each accident reconstruction method and knows what can be learned from each method. They know when not to apply a particular method. 

10. The competent accident reconstructionist knows how to document the physical evidence types from a crash. Common tools used for this include:

    • Camera 

    • Total Station

    • Laser Scanner 

    • Camera-Equipped Unmanned Aerial System 

    • Pocket Rods

    • Checklists and forms

11. The competent accident reconstructionist understands and applies photogrammetric techniques to reconstruct the locations of pieces of physical evidence that are no longer present during a site inspection or to generate terrains for use in analysis. For example:

    • Camera-Matching 

    • Photomodeler

    • Pix4D

12. The competent accident reconstructionist understands the importance of documenting the physical evidence on a scale diagram. They see this as a primary underpinning of a well-founded accident reconstruction. They also understand common measurement methodologies used by police investigators and can interpret police measurements. 

13. The competent accident reconstructionist can select an appropriate range of values for the coefficient of friction, the drag factor, or the acceleration rate for a wide variety of situations. They understand the differences between these quantities.

14. The competent accident reconstructionist can integrate event data from a passenger vehicle EDR into a reconstruction alongside other types of evidence (physical, video, audio, testimonial). The have a grasp of the expected error rates for various quantities reported by an EDR.

15. The competent accident reconstructionist can integrate event data from a heavy truck EDR into a reconstruction alongside other types of evidence (physical, video, audio, testimonial).

16. The competent accident reconstructionist can determine a reasonable range of perception-response times for a driver in a particular crash scenario.

17. The competent accident reconstructionist takes witness statements and testimony seriously and uses them in their accident reconstruction. The competent accident reconstructionist recognizes that witnesses are generally inaccurate when estimating times, distances, and speeds. They also recognize that witnesses have biases and motivations that may lead them to lie or describe events incorrectly. However, the competent accident reconstructionist does not have a dismissive attitude towards witness accounts. They use physics and physical evidence to test what witnesses say.

18. The competent accident reconstructionist can apply techniques of uncertainty analysis to determine which variables are most significant to a reconstruction and to establish a range on a calculated value.

19. The competent accident reconstructionist will develop at least one area of specialized expertise. Areas that come to mind include:

    • Imaging passenger car EDR data

    • Imaging heavy truck EDR data

    • Specializing in a specific area of accident reconstruction:

      1. Rollover

      2. Pedestrian

      3. Motorcycle

      4. Heavy Truck

20. The competent accident reconstructionist is familiar and conversant with a wide swath of the accident reconstruction literature.

21. The competent accident reconstructionist has an active reading and research practice that is moving their expertise forward. 

Mastery of Accident Reconstruction 

You do not become an expert in accident reconstruction simply by achieving technical competence. As your expertise progresses, you will take on the following characteristics that are evidence of a growing mastery of accident reconstruction. When you take on these characteristics, you are becoming well-equipped to testify and to lead projects.

1. You have become skilled at identifying key questions and issues for individual cases. You know how to define the scope of work to address these questions and issues in a way that accounts for limitations in the available evidence, budget, or time.

2. You know how to properly pair your findings and opinions with the available evidence. Your findings and opinions do not go beyond the evidence or outside the boundaries of your expertise. And yet, your opinions have a “so what” to them. They are not divorced from the issues of interest to the lawyers and fact finders involved in the case.

3. You understand the progression of the investigation and analysis of an accident. Your investigation and analysis unfolds in a logical and efficient progression. As an example, you do not attempt to simulate the crash before gathering the physical evidence. You first learn all you can from the physical evidence and spend time establishing reasonable ranges for the simulation inputs (coefficient of restitution, friction coefficients, etc.).

4. You are able to move a case efficiently through the investigation and analysis process to reach well-founded conclusions. You are able to direct others in this process.

5. You recognize that all models are wrong, but most models are useful. You do not dismiss or needlessly criticize models or methods. Instead, you have invested the time to have many models available in your toolbox, and you know which tools to use on any given case. 

6. You are aware of emerging issues and technologies in the field and you are taking regular action to update and improve your skills in these emerging areas.

7. You are comfortable working with attorneys. You recognize the unique ways that attorneys process information and you have made your peace with it. You don’t demonize the way that attorneys think.

8. You are committed to the truth. However, you do not confuse the truth with your analysis and opinions. You strive to be rational and reach well-founded conclusions, but you recognize that you are capable of making mistakes and being biased. You entertain the possibility that you might be wrong.

9. You understand and apply appropriate terminology around causation.

10. You understand how to define reasonable and justified hypothetical scenarios. 

The Consummate Expert in Accident Reconstruction 

Beyond mastery, you may achieve a level of expertise that puts you a leader in the field.

1. At this level, you have become an accident reconstructionist that others, both inside and outside of the company, strive to emulate. 

2. Other experts, both inside  and outside of the company, seek out your expertise and opinions.

3. You know how and when to break the rules. For example, you may choose to simulate a crash before gathering the physical evidence, simply to develop an understanding of what variables are significant. You are capable of doing this without over-committing yourself to a particular theory of the case. You remain open to the physical evidence that you will discover later in the process.

4. You invest significant effort in disproving your own theories and opinions.

5. You can critique the other side’s experts without losing the ability to learn from them.

6. You quickly recognize the issues and questions that will be relevant to a case.

7. You recognize the distinction between your role and the role of the attorneys and other experts on a case. You hold a level of detachment from the case and do not demonize or dismiss either side in the litigation. You figure out what you can learn from the other side - you figure out what you can learn from everyone - and you take seriously your role of providing the jury with useful and educational information that will help them make a good decision.

8. You recognize that we are consultants. You are open to any and all questions from our clients. You treat each question with respect and give it a real answer. If the real answer is “I don't know,” then you say that.

9. You give direct and clear answers to cross-examination questions. You are not evasive in your answers because you have become comfortable with any and every question. You know how to engage inappropriate or manipulative questions in a professional manner.