While bankrupt General Motors is discontinuing its line of medium-duty trucks, the clock is ticking for others to clean up tailpipes in January. The clean-air regulation has Warrenville, Ill.-based Navistar International Corp. asking a U.S. appeals court in Washington, D.C., to review a February ruling by the U.S. Environmental Protection Agency. The EPA action provided guidance to diesel-truck makers on how to certify engines using selective-catalytic reduction. Navistar alleges EPA in 2001 did not deem SCR permissible due to the use of liquid urea, of which distribution and handling was questionable. Other producers argue urea is proven. Navistar is the
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.