The U.S. Environmental Protection Agency's proposed rule on diesel exhaust emissions won't be final for months yet and, if adopted as proposed, not fully effective until the year 2010. The agency is proposing a 90% reduction (from 2004 levels) in NOx pollution and up to a 97% reduction (from current levels) by 2006 in sulfur levels in diesel truck and bus fuel. By why wait? asks the Arlington, Va.-based Natural Gas Vehicle Coalition, a group trying to seize a market opportunity created by the proposed regulation. "Many heavy-duty natural gas trucks and buses available today already meet the very stringent proposed particulate standard, and produce up to 50% less nitrogen oxides than comparable diesel vehicles," says Richard Kolodziej, president of the 180-member coalition that includes natural-gas-equipment manufacturers and service providers.