Over the Hill


Expertise Includes:

    • Vehicle Collision Reconstruction
    • Crash Data Retrieval
    • Forensic Mapping Technology
    • Motorcycle Collision Reconstruction

When traveling down the roadway, a lot of things must be considered. While things that can be seen are obvious concerns, things that cannot be seen pose a threat too. Blind hillcrests leave drivers guessing “what’s on the other side”. Regardless of their intentions, before drivers make a maneuver, they should pay extra attention to blind hill crests. In a collision that occurs just over a hillcrest, where one driver is attempting to continue straight as the other is attempting to make a left-hand turn, many times the investigating officer arrives at a common conclusion. Failure to yield right of way charges are often applied to the driver making the turn; however, are these charges applicable?

Blind Crest Roadsign



In this scenario, the speeds of the vehicles involved need to be determined. This can be done by completing speed calculations, which requires crash scene documentation of the collision.  Hopefully, evidence such as skid marks, yaw marks and other physical evidence are still visible. Speed can also be found by imaging the Event Data Recorder (EDR) information that will most likely be available in modern vehicles. An analysis of this data will give the most accurate speeds if the system functioned properly and the vehicle’s safety system was engaged. An investigation is more involved than “was anyone speeding?”.

To understand the sequence of events involved in this type of collision, a reconstructionist must complete a time distance study of the crash. Much like the speed calculations, they will need a documentation of the collision scene. Whereas in speed calculations they are looking for the positions of the vehicles at the beginning of skids, the point of impact, and final rest so they can determine how fast the vehicles were traveling; in a time distance study they are looking for how much distance did the vehicles cover at the determined speeds and where were the vehicles in relation to each other when things begin to transpire. In the example of a blind hillcrest, was the vehicle attempting to continue straight visible to the driver on the other side of the hillcrest that was attempting to make a left turn? Using the speed that the vehicle was traveling as it attempted to travel straight through in conjunction with any speed that vehicle lost from skidding, that vehicle must be backed up from the impact with the turning vehicle. Likewise, using the determined speed of the turning vehicle, that vehicle must be backed up from the impact. Using mapped data from the collision area, a scaled diagram can be derived from the collected data.

Mapped data will give lateral and longitudinal locations and the elevation of mapped points. A scaled diagram using this data will capture the slope and superelevation of the roadway for a 3-D depiction of the crash scene. With vehicles in the diagram scaled to match the width, length, and height of the vehicles involved in the crash, perspectives set at the measured heights of the drivers of the vehicles will show what they were able to see or not see as they maneuvered on the highway in the proximity of the hillcrest. From the view of the vehicle turning left, can they see the vehicle that is approaching them? Which leads to the question, how can they yield to something they cannot perceive? If the vehicle continuing straight was found to be above the posted speed limit (it is always good to know where and when the speed limit sign was erected), does that influence the collision?  This is also a good place to point out that mapping the damage profiles of the vehicles helps to show how much of the vehicle was able to clear the area of impact, and how much had not cleared at the time of the collision.  If the impact to the turning vehicle is at the frontmost portion of the vehicle, then it is obvious that it still needed a lot more time to clear the crash area than if the impact was to the rearmost portion of the vehicle.

a road crest at the top of as hill

A road crest at the top of a hill

Once it is determined where the vehicles were as they approached the collision, the investigator can now look at the factors that could be changed to keep the collision from happening.  Did the driver of the turning vehicle turn too slowly and hesitate to cause the crash?  Was the driver of the vehicle continuing straight through traveling above the posted speed limit?  If they had been driving the speed limit,  would the collision still have happened?  Does the State Department of Transportation have a contributing factor in the collision because of their roadway design in relation to the posted speed limit?  The answers require time, distance and a thorough reconstruction.

Aaron (Al) Duncan II, ACTAR, is a vehicle collision reconstructionist with Warren and President of SCARS. Prior to joining Warren, he worked for 23 years as a South Carolina Highway Patrol Trooper to include 10 years as a Multi-Disciplinary Accident Investigation Team (M.A.I.T.) member. Al is accredited as a Traffic Accident Reconstructionist by The Accreditation Commission for Traffic Accident Reconstruction. He investigated in excess of 1000 vehicle accidents and incidents, as a trooper. Then, as a member of M.A.I.T. for 10 years, he was involved in over 1000 detailed investigations and collision reconstructions. Al has testified multiple times in state courts and he has been court qualified as an expert in accident investigation and collision reconstruction. Al’s work expertise focuses on investigating and reconstructing vehicle collisions involving single and multi-vehicles, animals, pedestrians, motorcycles, heavy trucks, and commercial vehicles. He is also a skilled user of forensic mapping technology and computerized collision diagramming software for collision scene analysis. Al is experienced in the data download and analysis of airbag black boxes (Crash Data Retrieval Units) in automobiles, pickup trucks, and SUVs. He holds a Bachelor of Science Degree in Political Science from Lander University in Greenwood, South Carolina and completed the Law Enforcement Basic Program at the South Carolina Criminal Justice Academy in Columbia, South Carolina.

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