On May 11, the U.S. Environmental Protection Agency unleashed a new clean-air rule that further cuts diesel emissions from off-road vehicles, generators, locomotives and marine vessels. The new “Tier 4” mandate is EPA’s fourth step since introducing off-road standards in 1996, and it lowers such pollution by 90% (ENR 6/23/03 p. 13). The rule varies across engine sizes, but most producers will reduce nitrogen-oxide levels in new engines to 0.3 grams per brake-horsepower-hour and particulates to 0.01 g/bhp-hr by 2014. Under the new rule, EPA is not requiring pollution controls on existing machines in the field. Off-road fuel also is...
