In 1999, Ramamurthy and Clark [7] discussed the contribution that heavy-duty vehicle emissions make to the
atmospheric NOx levels for 1994-1999 MY trucks. This paper attempts to extend that work by providing emissions data found for typical 2003-2005 MY heavy-duty trucks by analyzing the data in a manner similar to the
one followed in reference [7], and to compare some of the interesting data with those of 1994-2002 MY trucks.