The following four methodologies are primarily used in collision analysis: 1. the energy method, 2. the momentum or amount of motion method, 3. the dynamic method, and 4. the kinematic method. Of these four methods, the momentum method is the most commonly used because applies the principle of conserving the amount of movement, equalizing the momentum of the vehicles before and after the collision, allowing the determination of the initial speed and will be considered in the development of these book. In crash investigations, two or more techniques are usually used to analyze the convergence of the results and, as the energy method is a powerful tool for determining speeds before impact, it is usually used as a complement to the momentum conservation method.