The cause was also joined by environmental groups and activists who, among other things, famously photographed a tank car carrying chlorine with the nation's Capitol building in the background. That began a push to get such shipments detoured around metropolitan areas and heavily populated areas.
A handful of major accidents, including a 2001 freight train derailment near Minot, N.D., drove home the activists' point. In that case, five tank cars carrying ammonia gas broke open, releasing toxic fumes that killed one and injured 1,441, federal data show. In 2005, a train collision in Graniteville, S.C., broke open one tank car loaded with 90 tons of chlorine, releasing about two-thirds of the gas. Nine died and 252 were injured.
Following the North Dakota accident, the National Transportation Safety Board (NTSB) in a 2004 study concluded that more than half of the 60,000 rail tank cars used to transport hazardous materials at that time were not built according to standards and were susceptible to rupture in the case of an accident.