Robert T. Lynch, PE, Sr. Collision Reconstruction Engineer ::::
In order to determine whether or not a collision was avoidable, the question that is often posed to the reconstructionist is: What could or could not be seen at the time of the incident?
Answering this question for collisions occurring under daylight illumination is a straightforward approach. The engineer/investigator visits the site and takes photographs from viewpoints of interest that depict the field of view that would have been available to a vehicle operator. Measurements taken during the site inspection compliment the photograph to specify the available sight distance that is visually represented.
However, using photography in nighttime collisions to represent what a driver could or could not see is more involved. Specifically, the lighting conditions at night (vehicle headlights, streetlights, lane striping, etc.) play a large role in determining when an object/vehicle/pedestrian presents itself as a hazard, and thus, play a critical role in determining whether or not a collision was avoidable.
Assuming that the challenge of matching the lighting conditions during the night inspection/recreation to represent the conditions at the time of the collision can be reasonably met, the exercise then is to obtain a photograph that provides a fair representation of what was available to be seen. The general approach involves placing a contrast chart in the recreated scene, such as at the position of a pedestrian, and then to have an observer view the chart from a position of interest, such as the driver seat of a vehicle on a path heading towards a collision.
The observer records the minimum contrast levels visible on the chart. Several photographs of different exposure settings (exposure can be effectively visualized as image brightness/darkness) are taken from the same vantage point as the observer. The same set of photographs are taken with the chart removed from the scene. When the photographs are then printed/displayed, the observer selects the photograph that yields the same minimum detectable contrast level for the chart as was recorded while at the scene. The photograph with the same camera exposure settings without the chart is then a validated representation of the lighting conditions.
Nighttime photography is a valuable tool to represent the lighting conditions available to the investigating observer at the time of the recreation, and thus arguably the same as was available at the time of the incident, if the conditions and illumination were set up correctly.
For more information about using nighttime photography for collision reconstruction, contact Robert T. Lynch, PE, Sr. Collision Reconstruction Engineer at DJS Associates, at 215-659-2010 or via email at firstname.lastname@example.org.