This expanded and updated third edition continues to be an essential reference volume in regards to the principles and techniques of traffic crash investigation. One of the most important phases of any investigation into a traffic crash is that which is conducted at the scene. The traffic crash investigator must be aware of his or her responsibilities and know how to properly fulfill them from the time of being advised of a crash to the time the report is completed based on the on-scene investigation. This manual sets out in detail the requisites for a properly conducted crash investigation by delineating the types of evidence to look for and how to recognize, interpret, gather, and record evidence such as skid marks, yaw marks, roadway and vehicle marks and damages, and environmental, human, and mechanical factors. Only by understanding the principles presented in the text will the objectives of a traffic crash investigation be met: what happened, where the crash occurred, why the crash occurred, and who was involved. The manual covers in both written and illustrative form those situations that confront the investigator conducting a technical crash investigation. An important introduction to scientific speed analysis based on thorough at-scene investigation is provided. Mathematical equations and examples are completed in both the United States or Imperial and metric (S.I.) measurement systems. The book is generously illustrated and substantial appendices provide helpful mathematical tables. This invaluable resource will meet the needs of law enforcement officers, insurance adjusters and investigators, private investigators, lawyers, judges, legal investigators, and instructors and students involved in cadet or advanced traffic crash investigation programs. This new edition will be appreciated by all those charged with the responsibility for investigating traffic crashes, interpreting data, and presenting evidence based on sound analysis.