Innovators Research, Inc.
Michael L. Shirley, PE
Athena Research & Consulting LLC
Shelton Investigations, LLC
American Academy of Forensic Sciences
iri Case Studies
Defective Brakes or Driver Error?
A tractor pulling two dump trailers loaded with hot asphalt, was unable to negotiate a sharp curve near the bottom of a long downhill grade. The driver bailed out of cab prior to rollover, and claimed the brakes failed. iri staff inspected the tractor & reviewed a trailer inspection report from another expert, as trailers were no longer available to iri during our investigation. Based upon tractor-trailer tire marks leading up to the curve and driver deposition testimony, the driver’s failure to properly utilize air brakes and the tractor’s “Jake Brake”® were concluded - after applicable engineering analysis and calculations - as being the most probable cause of the excessive speed rollover. The case was resolved with no expert testimony.
Driver Error or Pre-Collision Damage?
After going over a very rough RR grade crossing at approximately 45 MPH, that was at an angle to a rural highway, a tractor-trailer entered the oncoming traffic lane and collided with an approaching pickup truck. The tractor-trailer driver testified the tractor’s steering wheel jerked as he crossed the RR tracks and that he had no steering control afterward. The driver applied brakes, leaving tire braking marks leading up to the collision, and a component of the tractor’s steering linkage was found to be fractured after the collision. Several experts concluded the steering component fracture resulted from the collision with the pickup truck and that driver error caused the accident. iri staff became involved and after carefully reviewing the existing evidence, initiated a detailed examination of internal components of the tractor-trailer’s steering gear, which revealed damage-induced impact witness marks on internal components. These internal witness marks were not consistent with damage that would have been created during the collision with the pickup truck. The fracture origin on the steering linkage component was also inconsistent with pickup truck induced collision damage.
Immediately after the accident, investigators had documented a 11” deep hole in the RR crossing ballast, partially covered by a “rubber” flexible driving mat with a seam between adjacent mat sections, that was over the main portion of the hole. A steer axle wheel of the tractor, dropping into an 11” deep hole at 45 MPH at the driving mat seam, with the tractor crossing the RR at an angle, would produce impact forces to the steering linkage, transmitted to upstream steering components, of sufficient magnitude to produce the steering linkage component fracture and corresponding witness marks within the steering gear - consistent with the physical evidence - and the driver’s testimony of no steering control after the RR tracks. Driver inattentiveness was not an issue, as he had applied the tractor-trailer’s brakes, leaving braking tire marks, prior to the collision.
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