Night Visibility Evaluation
How do you determine what a driver could, or could not see and perceive in the dark?
This is the kind of question we are asked to answer often given our expertise in the areas of night visibility and conspicuity.
Case Study – Visibility of a Disabled Tractor-Trailer
In this particular case there were actually two collisions.
The first, a night-time collision of a passenger vehicle with a tractor-trailer rig which left both vehicles disabled in the middle of the intersection.
The second, an oncoming passenger vehicle approaching from another direction which fails to avoid the disabled truck and under-rides the trailer, leading to severe passenger compartment intrusion.
Evaluate the visibility of the tractor-trailer prior to the second collision and determine if there was adequate time and distance for the decedent to perceive, react to and avoid the accident.
Accidents at night are unique because, in part, vision under low light conditions is different than during daytime conditions. Evaluating visibility at night requires an understanding of how the eye works and how humans perceive. "Visibility" and response to a disabled vehicle are a function of the information received and interpretation of this information.
In this case, the best practices for accident reconstruction were used to set up the scene and allow S-E-A engineers to evaluate visibility and perception under the circumstances particular to the case at hand.
S-E-A reconstructed the accident using carefully matched vehicles, including a detailed match of the reflective materials present on the original tractor-trailer.
Law enforcement closed the roads as the accident was reenacted.
The recreation was performed at the original scene, at the same time of day and with the same lunar conditions as the incident.
S-E-A captured nighttime-calibrated photos and videos of the reenactment.
Test evidence was evaluated and resulted in the following findings:
- In all cases and for all tested conditions, the tractor-trailer was found to be visible from the position of the driver of the car.
- There was enough time and distance available to the driver of the car to recognize that the tractor-trailer was in the intersection and stopped, perceive the vehicle as a hazard and avoid the accident by braking to a stop and/or slowing and steering around it.
While high-end photographic and luminance measuring tools were used in this case, the specialized knowledge involved is far more important.
An in-depth understanding of human visual abilities in low or adverse light conditions is what allows for proper replication, measurability and analysis of what is visible from varying distances under a variety of conditions. Our decades of experience in accident reconstruction combined with an intimate knowledge of the capabilities and limitations of the human eye is a powerful combination indeed.
S-E-A’s multi-disciplinary teams are a large part of the reason why we have been able to help so many clients. Our scientific methodologies cross all disciplines and our wealth of experience solving a wide range of problems is invaluable in assuring broad perspective and thinking unfettered by familiarity and repetition.
For more information about reconstruction of accidents in low or adverse light conditions, contact:
Fawzi P. Bayan, P.E., CSP