The next phase of U.S. regulations aimed at cleaning up airborne emissions from off-road diesel engines will start taking effect in just nine months. The rule, called Tier 4, will all but eliminate the amount of diesel particulate matter (soot) and nitrogen oxides (NOx) that new construction equipment will put into the atmosphere. Photo: Caterpillar Inc. Photo: Caterpillar Inc. Cat’s Clean Emissions Module—the Tier 4 excavator at left uses one—will fit on new and existing engines. The particulate filter can regenerate, or burn soot, without idling the machine. Related Links: Three Ways Manufacturers Will Meet the Tier 4 Standards 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.