It is generally conceded that, under ideal circumstances, the best source of information regarding the sequence of events surrounding a vehicular accident lies in accurate, complete, and absolutely reliable eyewitness accounts. When, however, as is most often the case, eyewitnesses are missing or the information which they provide is incomplete or conflicting, it is necessary to rely upon data derived from the evaluation of physical evidence recovered from the accident scene and from the vehicles themselves. Evidence of this kind is likely to include glass, paint, soil, fractured metal surfaces, and, frequently overlooked, headlight and taillight filaments, the microscopic examination of which provides information relating to the operating condition of the vehicles' headlights and taillights before, during, and after the accident.