Nighttime visibility is an important consideration in collision reconstruction and personal injury investigation. Decreased contrast in low ambient lighting conditions can greatly affect human perception and response. Because ambient lighting levels change rapidly at dawn and dusk, forensic investigators must have an accurate knowledge of the time of day and the cloud conditions at the time of the incident before initiating a nighttime visibility assessment. Previously, human factors experts attempting re-enactments at dawn or dusk have had to wait for sky conditions that match those at the time of the incident, making the investigation of those cases extremely difficult, if not unfeasible. In this study, an ambient illumination equivalency tool has been developed based on a database of time-lapse light meter readings collected by the authors. This new tool can be used to facilitate nighttime visibility assessments on any day by providing a time adjustment factor to account for the changes in ambient illuminance due to differences in the cloud conditions between the day of the incident and the day of the re-enactment.
Investigation of nighttime motor vehicle collisions represents one of the most challenging aspects of collision reconstruction. Nighttime collisions with motorcycles, pedestrians, cyclists, skateboarders, or wildlife will often require the investigator to assess the visibility of the struck object from the driver perspective at the time of the collision. Since lighting conditions, weather conditions and traffic conditions are continually changing, the ability of the investigator to create a perfect re-enactment is, by definition, not usually possible. As such, the investigator must make use of nighttime visibility assessment techniques to best reproduce the conditions at the time and correctly account for all other factors that are not in the investigator’s control. The goal of this panel discussion session is to share the combined experience and knowledge of the panelists with the audience regarding the tried-and-tested best practice techniques and tips of conducting nighttime collision re-enactments.
In collision reconstruction of nighttime accidents, the conspicuity of hazards from a driver's perspective is a critical factor. When the collision involves large commercial vehicles, the visibility of the reflective strips is essential in assessing avoidance. Reflective strips on commercial vehicles are generally consistent from vehicle to vehicle and are highly reflective between perpendicular and 45° viewing angles. However, at shallower viewing angles (closer to parallel viewing), which occurs when trailers begin turns, the reflective strips may not be effective. In this initial study, the effectiveness of reflective strips at shallow viewing angles (‘entrance angles’ of 45° to 90°) was examined under a variety of test conditions including high beams and viewing distances of up to 150 m. The results indicated that at entrance angles of less than 70°, reflective strips are highly effective warnings from a human factors perspective. At entrance angles of more than 75°, reflective strips are ineffective. From 70° to 75°, the results were sensitive to the test parameters. This study does not address the visibility of the tractor or other aspects of nighttime visibility. Further research is recommended to extend this study to greater viewing distances, xenon headlights, ‘dirty’ vs. ‘cleaned’ reflective strips, and wet roads, with particular attention to entrance angles of 70° to 75°.
Professionals who are allowed by a court to serve as expert witnesses are granted the special legal status of offering opinion and theoretical evidence based on human factors research and provided facts that the expert did not witness themselves. The role of the Human Factors forensic expert in U.S. and Canadian court cases has become more common over the past two decades as lawyers become increasingly aware of the specialized nature of this field of study. U.S. and Canadian Human Factors experts sometimes find themselves being retained by firms on the other side of the border due to their specialized experience and training in a particular area relevant to the case at hand. In such situations, the expert will need to deal with differences in legal systems and differences in client expectations between the U.S. and Canada. The goal of this panel discussion session is to share the combined experience and knowledge of the panelists with the audience regarding the most significant differences between U.S. and Canadian clients, courtrooms, and procedures in forensic testimony, so that the expert knows what to expect when accepting a cross-border retention.
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