Abstract: At approximately 8:55 a.m. on October 12, 2006, Employees #1 through #3 and a coworker were replacing reflectors between two northbound lanes of a highway. The crew was using a mobile operation work zone system, in which there were two shadow vehicles behind the truck actually performing the maintenance work. Shadow vehicle #1 was approximately one-quarter to one-half of a mile ahead of shadow vehicle #2, a pickup truck with a flashing arrow board advising oncoming traffic of the work zone in the right lane. Shadow vehicle #2 was not on the roadway. Shadow vehicle #1 was parked on the road in the right lane, 80 to 100 ft behind the work vehicle; it was equipped with a truck-mounted Safe-Stop 180 TMA attenuator, as well as a flashing arrow board and a RIGHT LANE CLOSED sign. Employee #1, the crew foreman, had gotten out of shadow vehicle #1 to help Employees #2 and #3, who were with the work vehicle, prepare a series of reflectors for installation. All three employees were standing at the tailgate of the work vehicle when a tractor trailer traveling north on the highway failed to merge into the left travel lane. It was moving at approximately 55 mph when it struck shadow vehicle #1, pushing into the rear of the work vehicle and its tow-behind air compressor. The compressor struck Employees #2 and #3, throwing them off to the right. Both sustained injuries that required hospitalization. Shadow vehicle #1 landed on the left side of the work vehicle, crushing and killing Employee #1. At the time of the accident, there was no precipitation, the road was not reported to be wet, and no obstructions to visibility were reported.