ITHACA, N.Y. -- Even the low-level but chronic noise of everyday local traffic can cause stress in children and raise blood pressure, heart rates and levels of stress hormones, reports a new study by a Cornell University environmental psychologist and his European co-authors. "We also found that girls exposed to the traffic noise become less motivated, presumably from the sense of helplessness that can develop from noise they couldn't control," says Gary Evans, an international expert on environmental stress, such as noise, crowding and air pollution.