In a bid to improve safety and reduce the number of freight-train crashes in which hazardous chemicals are released, the Association of American Railroads' Tank Car Committee has approved new design requirements for tank cars carrying chlorine and anhydrous ammonia. The new standards call for thicker steel shells and extra padding to protect the tops and ends of tank cars. The committee says the redesign will reduce the chance of a release during an accident by at least 65%. The standards are scheduled to take effect in January. The existing fleet would have to be retrofitted over the next 11 years by adding a layer of steel to each tank's exterior. The modifications would add about $30,000 to retrofit a car that now costs $100,000. Chemical shippers say any effort to change tank-car standards should be guided by congressionally mandated research currently under way at the Department of Transportation. Findings are due next year. Shippers also question whether the "heavier is better" approach will significantly improve tank-car safety and argue that railroads need to improve track maintenance and operations. DOT relies on the expertise of the tank-car committee to establish detailed design standards and has historically accepted the panel's recommendations.