The main objective of this paper is to provide the research community with power specific CO2 and NOx emissions levels for the 2003-2005 MY heavy-duty vehicles. Five different trucks were tested on the UDDS and the
transient and high-speed cruise modes of the HHDDT. For all the cycles, the emission rates increased with increasing power. However, the linear dependence of mass rate on power was different for CO2 and NOx. The CO
2
mass rate was correlated well with the power (R
2
= 0.85), but the R
2
value for correlation of NOx with power
(R
2
= 0.50) was significantly lower than the R
2
value for correlation for earlier MY vehicles (R
2
= 0.85 from the
study by Ramamurthy and Clark [7]). This is attributed to the complex emission controls employed by the modern trucks. For example, with multiple injections or cooled EGR in use, NOx emissions are governed less simply
by injection timing. The cycle-to-cycle variation of the emission rates was studied and second-degree polynomial equations were developed for each cycle. The effects of three test weights on the emission rates were presented. The linear fits for the three weights had similar slopes and intercepts. This suggested that the test weight