Abstract: At approximately 10:00 a.m. on October 21, 2003, Employee #1, a heavy equipment operator under training as an electrical technician, and a coworker, were replacing street traffic lights at an intersection. They drove separate vehicles, Employee #1 in a pick up truck and the coworker in a truck mounted hoist with an articulating boom aerial device. The pick up truck was parked at the outer-most lane of the southwest bend of the intersection facing south. The coworker placed a cone to block traffic on that lane. The light to be replaced was above the second lane. The coworker, a tree maintenance worker, was also under training as an electrical technician. At approximately 9:30 a.m., they had a job briefing and then parked the aerial lift truck under the traffic light to be replaced, and placed cones along side it. Employee #1 stated that they were not told to block the traffic lane under the boom basket, only the area around the truck. Employee #1 climbed in and rode the boom basket up. The coworker saw the bottom of the basket as it went up, then went to retrieve some lamps. He heard a noise as a truck hit the aerial truck. The coworker saw Employee #1 hanging from the boom basket by her safety harness. She was hospitalized with body cuts and burses.