Nighttime Visibility
Saturday, July 1, 2023
by: Neal Carter, Explico

Section: Spring 2023

Explico Case Study: Nighttime Visibility Case from Explico on Vimeo.

Neal Carter and the Explico team analyzed an impact between two tractor-trailers. According to the police investigation and provided documents, the collision occurred at approximately 2:00 a.m. The first tractor trailer was initially traveling northbound on the Interstate, when it crossed the center median into the southbound lanes and became disabled, with the trailer across both southbound lanes and the southbound shoulder. Four southbound drivers were able to successfully stop their vehicles on the shoulder of the southbound lanes without impacting the tractor or trailer. A second tractor-trailer was southbound on the Interstate and approached the stopped passenger vehicles and the disabled tractor-trailer. The tractor-trailer heading southbound passed the vehicles that were stopped on the shoulder and impacted the disabled trailer.

The southbound tractor was equipped with a Lytx DriveCam system, which records forward facing video, rear facing video, audio, longitudinal acceleration, lateral acceleration, and GPS-based vehicle speed. The images below are frames taken from the forward-facing video. These frames depict the southbound tractor trailer traveling past the passenger vehicles that are stopped on the shoulder and the collision.

Accident Scene Documentation
The investigative agency documented the scene of the subject collision photographically. The images below depict the position of the northbound tractor and trailer at rest after the trailer was impacted by the southbound tractor. The impact caused the trailer axles to separate from the frame and caused the trailer to rotate. These photographs also depict the passenger side door, door frame, and mirror of the colliding tractor lodged into the side of the trailer.

Video Analysis
Neal Carter and the Explico team analyzed the video provided from the Lytx DriveCam system that was installed on the southbound tractor. The DriveCam system records forward facing video, rear facing video, audio, longitudinal acceleration, lateral acceleration, and GPS-based vehicle speed. This data is recorded in a loop and when the system detects acceleration greater than a user-defined threshold, the system writes the recorded data to memory. In this case, the system recorded for eight (8) seconds before the triggering event and four (4) seconds after the triggering event. The system exports a video file that displays 10 frames of video per second with the corresponding measurements overlaid on the video. Video frames and measurements that occur before the triggering event are given a negative time stamp, and video frames that occur after the triggering event are given a positive timestamp. The timestamp on the subject video progresses from -8.00 seconds to +4.00 seconds, for a total of 121 frames of video.

The driver-facing portion of the DriveCam video was black for the entire duration of the event. The forward-facing portion of the video showed the northbound trailer across the travel lanes. In the video, the northbound trailer is visible from the beginning of the video (-8.00 seconds) to impact. In addition, four vehicles are shown stopped on the shoulder of the roadway. The rearmost (northernmost) vehicle in the shoulder had its hazard lights activated, and a person is seen on the shoulder waving at the southbound tractor.

Explico utilized the technique of camera matching photogrammetry to determine the position of the DriveCam camera in the southbound tractor at various times before it impacted the northbound tractor trailer. In this instance, Explico utilized data from the United States Geological Survey (USGS) the 3D Elevation Program (3DEP). The USGS formed the 3DEP in 2012 with the purpose of collecting and providing standardized, high-quality lidar data of the United States. Lidar, a term that is an acronym for light detection and ranging, is a method of remote sensing. The images below show the lidar data that we collected for the area of the accident. This data can be incorporated into photogrammetric analysis to determine the location of physical evidence, including vehicle rest positions.

Based on the results of the photogrammetric analysis, the Explico team created the diagram below. This diagram depicts the location of the DriveCam camera at six points in time as the southbound tractor approached the disabled trailer. The diagram also depicts the orientation of the disabled trailer and the location of the four vehicles that were stopped on the shoulder. At the DriveCam frame labeled -8.00 seconds, the DriveCam camera was approximately 744 feet from the trailer.

Nighttime Visibility Study
Based analysis of the video, Mr. Carter and the Explico team conducted a visibility study that utilized an exemplar tractor and trailer to represent the disabled tractor and trailer, an exemplar tractor to represent the southbound tractor, and four exemplar passenger vehicles to represent the four vehicles that were stopped on the right shoulder to the north of the disabled trailer just before it was impacted by the southbound tractor.
During this visibility study, Mr. Carter evaluated and quantified the degree to which the exemplar tractor and trailer was visible from the cab of the exemplar tractor. In this study, the trailer was trailer was clearly visible from a distance of at least 750 feet. The findings of this study were consistent with the video retrieved from the southbound tractor DriveCam. The left image below was taken during the visibility study at a camera distance of approximately 750 feet from the trailer. For comparison, the right image below is a distortion-corrected image from the DriveCam video at time -8.00, when the camera was approximately 744 feet from the trailer.

It would have taken approximately 300 feet for the southbound tractor and semi-trailer to brake to a stop. The southbound tractor would have had to begin applying the brakes at the position shown at about -3.50 seconds in the DriveCam video. That frame is reproduced below for reference. From the analysis of the DriveCam video and visibility study, northbound tractor would have had a clear view of the disabled trailer for at least 4½ seconds before he would have needed to apply the brakes in order to bring the tractor and trailers to a complete stop before impacting the disabled trailer.  Below is a comparison of the calibrated video from the nighttime visibility study, and the original DriveCam footage.


Calibrated Visibility Study Video from Explico on Vimeo.