Particulate matter and its dispersion near urban roadways has become an issue of increasing concern because of the possible health risks to humans associated with the inhalation of small particulates. Despite the potential health risk, little is known about the concentration of particulates near urban roadways or the particulates emission rates of various vehicles. This research focused on particulate matter smaller than 2.5 micrometers (microns), typically denoted PM2.5, because of the high potential health risks of such small particles. Data were collected along roadways on the University of Washington campus. The results of the data collection and subsequent statistical analysis revealed, as expected, that urban buses are far and away the major source of particulate emissions and that buses with low exhaust pipes are more of a threat to pedestrian traffic. More interestingly, our findings suggest that procedure AP-42 for calculating particulate matter near urban roadways is grossly inaccurate, producing values that are one to two orders of magnitude higher than actually observed PM2.5 values.