Propelled by an increase in prescription narcotic overdoses, drug deaths now outnumber traffic fatalities in the United States, a Times analysis of government data has found. Drugs exceeded motor vehicle accidents as a cause of death in 2009, killing at least 37,485 people nationwide, according to preliminary data from the U.S. Centers for Disease Control and Prevention. While most major causes of preventable death are declining, drugs are an exception. The death toll has doubled in the last decade, now claiming a life every 14 minutes. By contrast, traffic accidents have been dropping for decades because of huge investments in auto safety.