The Environmental Protection Agency said Friday that cars and light trucks in the 2001 model year and later could safely use a blend of 15 percent ethanol mixed with gasoline, up from the 10 percent standard now in much of the country. The decision means that about 62 percent of all vehicles can now use the fuel. But the practical impact of the announcement on the fuel blend, known as E15, was not clear. An announcement in October that cars in the 2007 model year and later could use the blend has so far had little impact on retailers or...