A woman killed Monday after the bike she was riding collided with a pickup has been identified as Layn Stewart, 56, according to the Tarrant County Medical Examiner.The Arlington woman was hit about 12:15 p.m. in the 5900 block of West Pioneer Parkway near The Oakridge School in Arlington when she moved off the shoulder and into the roadway, police said.The truck driver stopped and tried to help the injured woman.Stewart was pronounced dead at Medical Center of Arlington, police said. Her manner of death was ruled an accident.The area where the crash happened is nearly a mile west of West Pioneer Parkway's intersection with Green Oaks Boulevard, on the west side of Arlington.Tiara Ellis Richard, police spokeswoman, said investigators believe that the woman, who wore a helmet and a backpack, was riding west on the shoulder of Pioneer Parkway."For an unknown reason, she went into the outermost lane of traffic on the roadway and was hit by the pickup, also heading westbound," Richard said. "In addition to witnesses and the driver of the pickup stopping to offer assistance, officers heading to the nearby Police Training Center also stopped to help the victim."Investigators, as of Monday afternoon, had not yet determined fault in the wreck, Richard said."There is no indication that the pickup driver was intoxicated at the time of the crash," she said. "The man is cooperating with investigators."