HOUSTON, July 23 (Reuters) - The Greenbrier Companies Inc  
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    said a two-year timeline for phasing out older railcars used to carry the most dangerous flammable liquids, including North Dakota's Bakken crude oil, is "aggressive," but can be done, a spokesman for the railcar manufacturer said on Wednesday.     Those comments came after the U.S. Department of Transportation proposed new safety standards for moving crude and ethanol by rail in light of several fiery accidents over the past year.  
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        The proposed standards suggest phasing out older cars built before October 2011, which is when the industry adopted a newer design with 7/16-inch thick steel hulls and reinforced valves to better protect against leaks in a derailment.     They also suggest several options for tank cars built after October 2015. Two options would have 9/16-inch thick steel and a third would maintain the 7/16-inch standard.     Oregon-based Greenbrier in February began marketing a newer tank car design with 9/16-inch thick steel, as well as stronger top and bottom outlet protection and an outer steel jacket with ceramic insulation.     Greenbrier last month said multiple customers had ordered 3,500 tank cars with that latest design.     This week Greenbrier and Kansas-based Watco Companies LLC, one of the U.S.' largest short-line railroad companies, formed GBW Railcar Services, a joint venture combining their 38 railcar repair, refurbishment and maintenance shops.     Jack Isselman, a spokesman for Greenbrier, said on Wednesday the company was ready for a regulation requiring a stronger railcar that can better withstand volatile Bakken crude with the joint venture.     "A two-year timetable for phasing out the use of older DOT-111 cars in the most hazardous flammable service is aggressive, but can be met with appropriate retrofit packages and new car design," he said.   (Reporting by Kristen Hays, editing by G Crosse)  ((kristen.hays@thomsonreuters.com)(+1-713-210-8538)(Reuters Messaging: Reuters Messaging: kristen.hays.reuters.com@reuters.net))  Keywords: USA OIL/RAILWAYS GREENBRIER