NCJ Number
200123
Date Published
March 2003
Length
33 pages
Annotation
This document provides information to prosecutors on the basic science, investigative techniques, and questions to ask on crash reconstruction.
Abstract
Evaluating fatal motor vehicle crashes is one of the more difficult challenges for prosecutors. Roughly 40 percent of all the fatal crash reports that prosecutors assess will involve impaired driving. After a crash, the prosecutor receives a written police report, and in many cases, a part of that report focuses on the reconstruction of the crash. The prosecutor can strengthen the investigation by critically assessing the reconstruction and playing the role of the devil’s advocate. Challenging questions must be asked. The prosecutor should be particularly sensitive to issues affecting the credibility of the potential police witness at trial. It is important for prosecutors to visualize the crash from the information in the report alone. Searching for gaps in the paperwork may suggest reasonable doubt later. Prosecutors often make the mistake of taking for granted proof of operation. The anatomy of a crash is composed of three chronological phases -- pre-impact, impact (engagement), and post-impact. Reconstruction fundamentals include energy analysis (motion energy), an analysis of speed from friction marks made by tires, and measurement with a drag sled (an accelerator attached to a vehicle). Since the drag factor is an important part of the reconstruction methodology, defense attacks attempt to lower the value measured at the scene by investigators. The length of a braking action is determined by the measurements of the tire marks on the roadway. Another method used to determine pre-impact speed is based upon the principle of conservation of momentum. The level of defense attack on the prosecution’s reconstruction is inversely proportional to the level of completeness of the prosecution’s investigation. Errors or omissions in scene processing, examining the vehicles, taking witness statements, and reconstructing the events provide attack points for the defense. The key to handling the adverse expert is preparation. 13 endnotes