At a West Coast intermodal facility, long trains were made up to carry goods to the interior states, ultimately for distribution to consumers. In this yard, semitrailers were brought in by over-the-road tractors to a drop-off area. Each trailer was then picked up by a spotting yard tractor and moved to a marshalling area.
With so many trailers coming into the drop-off area, the yard tractors were kept operating at a rapid pace. To keep up, a yard employee was pressed into temporary service as a spotter at the drop-off area to assist in guiding yard-tractor drivers.
The yard tractors were built especially for moving, or spotting, trailers within the yard. To engage a trailer, a "fifth wheel," typically slathered with grease, was located over the yard tractor's rear drive wheels. The fifth wheel is a flat plate with a central notch and a locking device that engages a heavy, vertical "king" pin at the bottom front of each trailer. To facilitate fast loading and unloading, the fifth wheel was raised and lowered by a hydraulic cylinder and linkage. This eliminated the need to crank up each trailer's landing gear (the small wheels under the front of the trailer) when moving, and cranking the landing gear down when parking.
Getting an all-clear yell from the temporary spotter who was on the right side of the tractor, the driver put the tractor in reverse, checked his side mirrors, turned his head to look out the back of the yard tractor, and backed up. He moved the fifth wheel upward to engage the trailer kingpin and raise the trailer to drive away, but the trailer appeared cocked to one side. Thinking that he missed engaging the kingpin, he lowered the fifth wheel and pulled forward, and started to call out to have the spotter re-direct his path. As he did so, he saw the spotter slide off the fifth wheel, leaving a trail of blood as the man fell to the ground. Emergency personnel were called to the scene and the injured spotter was taken to the hospital where he died the next morning.
I was retained by a lawyer representing the spotter's family to investigate the cause of the accident. Initially, I was very skeptical of this case, which seemed like a clear matter of negligence on the spotter's part, and failure of the tractor driver to keep the spotter in sight as he backed up. Still skeptical, but at the attorney's insistence, I personally inspected the accident site, the yard tractor, and the trailer. As I sat in the tractor, I could see that there were significant blind spots to the rear. The side mirrors, although very good for highway use, gave a good view to the rearward sides of the tractor but showed nothing behind the tractor. The tractor cab did not have a rear view mirror or even mounting holes for one.
I have always believed that the operator of a moving vehicle, or any machine for that matter, is the "captain of his ship." But I could see that this "captain" didn't have all the tools necessary to drive his tractor safely in reverse. I reviewed lab records of visibility tests for the tractor in question that clearly showed a lack of visibility to the right rear of the tractor, the side from which the spotter was trapped between the tractor and trailer. I also could see where a rear-mounted video camera and an in-cab monitor would have provided an extra measure of rear visibility.
In my opinion report, I cited negligence of both the spotter and the driver but also noted that better rear vision with a rearview mirror and a video camera might have prevented this tragic
accident. A question remained -- what caused the spotter to apparently dart between the tractor and trailer? The only clue was a greasy, bruised, and somewhat squashed cable and connector
that fed the trailer lights. This wasn't the clear "Omigosh" moment of discovery I relish, as I could only surmise that the spotter saw the cable and thought he could quickly pull it away to prevent it from being damaged. The case was not tried, but there was an unspecified settlement for the plaintiff.
This entry was submitted by Myron J. Boyajian and edited by Rob Spiegel.
Myron J. Boyajian, P.E., ([email protected]) is president of Engineering Consultants, a consulting service for forensic and design activities.
Tell us your experience in solving a knotty engineering problem. Send to Rob Spiegel for Sherlock Ohms.