I believe this refers to Tier II emission standards being applied in October of this year rather than in 2004 as originally planned. This is as a result of a consent decree signed by the DOJ, EPA, and the heavy duty diesel engine manufacturers back in '98.
It seems that the silly lawyers in Washington D.C. wrote some emissions regulations a few years back without understanding current and near term engine control technology. Some enterprising engineers at Cat, Cummins, Mack etc., implemented the regs in such a way as to maximize fuel economy at the expense of NOx emissions in engine operating modes not explicitly covered by the regulations. I guess it was assumed by the EPA that if they defined emissions standards at multiple engine operating points, the emissions performance would interpolate between the points. That's the way mechanical fuel injection systems would have worked. I guess no one ever bothered to do any research or even pick up a few copies of Diesel Progress. Apparently they missed the advent of computerised electronic fuel injection and engine control. Pin heads.
They get a new Peterbilt.