This book describes an orderly and science-based process of highway accident investigation, reconstruction and causation, beginning with the collection and interpretation of physical evidence, through the qualitative and quantitative reconstruction, to the determination of accident causation, with the ultimate goal of guiding the development of countermeasures. This process has evolved from the author's extensive teaching, research and reconstruction experience involving thousands of highway accidents, as well as the shared expertise of dozens of qualified investigators and engineers. Serious consideration is given to the role of police and civilian investigators in the process. Procedures are provided for the identification, collection, documentation and interpretation of the physical evidence upon which the entire process is dependent. Guidance is also provided in the qualitative reconstruction of accidents, thus providing critical information for subsequent quantitative reconstruction and causal analysis. Quantitative accident reconstruction proceeds from final rest backward through post-impact, impact and pre-impact phases of an event. The derivation and description of the vehicle and impact dynamics necessary for this reconstruction for a variety of crash configurations, as well as many example cases, are presented and discussed. An Accident Causation Model is offered as an orderly method for identifying human, vehicular, and environmental failures that cause a given highway accident. Analysis of the "second impact" includes a discussion of the methodology for determining occupant kinematics and injury causation, as well as suggestions for injury mitigation. Although this book is primarily directed toward investigators, reconstructionists and causal analysts, some topics will be of interest to professionals from a wide variety of fields such as attorneys, insurance adjustors, judges, and vehicle and highway engineers.