Crush & Speed Analysis Case 

Accident Reconstruction Summary

Kineticorp investigated an accident involving a 2015 Ford F-250 pickup truck, and a 2013 Ford F-150 pickup truck. According to the police crash report, Vehicle 2 (Ford F-150) was stopped facing westbound at the stop light at the intersection. Vehicle 1 (Ford F-250) was traveling westbound behind Vehicle 2, and Vehicle 1 failed to stop and struck Vehicle 2 in the back.  Kineticorp was hired to determine the speed of vehicle 2 pre-impact and post-impact.

The information below was derived and redacted from the actual Kineticorp expert report.  All names and identities have been changed.  For the full redacted report, contact Justin Holderness at [email protected].

Process:

In conducting this investigation, provided photographs were used in conjunction with the crash report and testimony from involved parties to analyze the accident. Kineticorp also inspected and investigated the accident site, and reviewed the provided documents.  Kineticorp performed a scene inspection at the accident site. Photographs were taken at the intersection of the accident, and a 3D laser scan survey of the scene was conducted. A total of five scans were conducted with more than 46 million points of data obtained.

 

Camera Matching Photogrammetry: Having created scaled three-dimensional models of the accident site and exemplar vehicles (2015 Ford F-250 and 2013 Ford F-150), Kineticorp used camera-matching photogrammetry to analyze photographs taken of the accident site.  The same method was used to determine the locations of vehicles in provided photographs and the damage to the subject vehicles. The vehicle rest positions that were identified and located using photogrammetry, were inserted into the scene diagram. Photogrammetry is a process that uses principles of perspective to analyze and obtain three-dimensional data from photographs or video. These principles and techniques are widely accepted and used within the field of accident reconstruction and computer visualization.

The photogrammetric process involves aligning the computer model with photographs such that the position and characteristics of the camera that took the image are matched in the computer environment with a computer-generated camera. The photographs below show the subject vehicles and the accident site matched with the 3D laser scans captured by Kineticorp. The photograph matching allows for accurate location and position of both subject vehicles’ rest positions in the 3D computer environment. Photogrammetric analysis was also used to determine the severity of damages to both

Accident Analysis: In evaluating this collision, Kineticorp analyzed the accident sequence of events using the completed 3D model of the accident scene, including camera-matched rest positions. A momentum analysis was performed using the post-impact travel distances of both vehicles to determine a range of impact speeds. We also analyzed the damage to the subject vehicles to perform an impact speed analysis to verify the impact speeds calculated in momentum analysis. The momentum and crush energy analysis methods, processes, and procedures used by Kineticorp in reconstructing this crash are widely accepted and utilized in the accident reconstruction community.

Momentum Analysis: Conservation of linear momentum utilizes the pre- and post-impact speeds of the vehicles as well as their respective weights. According to vehicle 2’s driver, he was stopped at the light for approximately 6 seconds before being impacted 7. A rollout deceleration test of modern vehicles was performed in 2012 by a Kirsten White, in which the rollout deceleration of a 2010 Ford F-150 equipped with rear-wheel drive was tested. This 2010 F-150 is within the same model year range (2009-2014) of the subject 2013 F-150, and therefore is substantially similar to the accident vehicle. Vehicle 2’s driver testified that the first thing he remembered after the impact was waking up on the side of the road, which indicates that he applied no driver inputs to the vehicle after the impact. With the post-impact travel distance, the vehicle and driver condition at the time of the collision, and the data presented in the rollout deceleration research paper, a post-impact speed for the F-150 was calculated. With the pre- and post-impact speeds of the F-150 known, the closing speed for the impact could be calculated. Because the pre-impact speed of the F-150 was zero mph, the closing speed of the impact is also the pre-impact speed of the F-250. Linear momentum analysis resulted in a closing speed, and therefore pre-impact speed of the F-250, of approximately 34 mph.

Crush Energy Analysis: The closing speed between vehicle 1 (Ford F-250) and vehicle 2 (Ford F-150) was analyzed through a crush energy analysis and compared to the momentum analysis. Crush measurements were calculated by comparing the camera-matched images of both subject vehicles’ damages to the exemplar vehicles inspected by Kineticorp. The images below show the camera-matched damage lines on the subject Ford F-150 used for crush analysis.  Crush energy analysis results in a closing speed for the impact of approximately 33 mph and Delta Vs for the F-150 and F-250 of approximately 20 mph and 16 mph, respectively.

Analysis Summary: Two independent methods were utilized in analyzing this accident: one method used conservation of momentum, and the other method used crush energy. Both methods used resulted in similar closing speeds and Delta Vs. The range for the pre-impact speed of the F-250 was found to be between 33-35 mph. This impact speed is consistent with the police findings of pre-impact skid marks and from Mr. Hill that he applied the brakes before impact. The Delta V of the F-150 was 20-21 mph and Delta V of the F-250 was 16-18 mph. Therefore, based on the speed analysis and the testimony, vehicle 1, the F-250, was traveling 70 mph prior to braking and impacted the F-150 between 33-35 mph.

Opposing Expert Video Analysis: A video file from the opposing expert witness was analyzed. The video is a representation of what they believed happened in the accident. The video shows the rest positions of both vehicles, which are consistent with Kineticorp’s findings. The video first shows contact between the vehicles happening between 56 and 57 seconds; the F-250 comes to rest approximately at 1:04, and the F-150 at approximately 1:10. At 1:59 the impact is shown again, and at 2:12 the F-150 comes to rest. From these times in the video, the impact-to-rest times of the expert’s reconstruction can be extracted: the impact-to-rest time of the F-150 is approximately 13-15 seconds, and approximately 8-9 seconds for the F-250. Using the distance from the point of impact to the accident vehicles’ rest positions, the average post-impact speed of the F-150 and F-250 would be approximately 34 mph and 20 mph, respectively. If a constant post-impact deceleration is used, the post-impact speeds would be 68 mph for the F-150 and 40 mph for the F-250. Therefore, the video simulation shows a Delta V of approximately 68 mph for the F-150, which far exceeds the values calculated by Kineticorp through momentum and crush energy analysis.

Conclusions: Based on the available evidence, testimony, and this engineer’s training, education, and experience, the following conclusions were reached:

• Vehicle 2 was stopped at a red light at the intersection.
• The F-150 came to rest approximately 755 feet from the point of impact.
• The F-250 came to rest approximately 260 feet from the point of impact.
• The closing speed of the impact between the F-250 and the F-150 was approximately 35 mph.
• Vehicle 1 was traveling approximately 70 mph prior to braking inputs.
• Vehicle 1 decelerated his Ford F-250 from 70 mph to approximately 35 mph prior to impact.
• The Delta V experienced by the F-150 was approximately 20 mph.
• The Delta V experienced by the F-250 was approximately 17 mph.

Do you want to learn more about this case, or do you have similar questions on one of your cases?  Contact Kineticorp’s Director of Expert Relations, Justin Holderness at [email protected].

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