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In emissions modeling, emissions released during cold starts are often underestimated, especially at the network level. This study quantifies the impact of cold-start emissions on human exposure during active travel (i.e., walking and bicycling) and while waiting at bus stops during the morning peak hour. Cold-start emissions of carbon monoxide (CO) are found to account for 90.2% and 77.9% of emissions on local roads and minor arterials. Neglecting cold-start emissions leads to an 82.0% underestimation of emissions at the network level. The results show that CO exposures are underestimated by 82.1%, 67.1%, and 88.8% for travelers walking, bicycling, and waiting at bus stops, respectively, when cold-start emissions are not considered. This study examines the significant contribution of cold-start emissions and recommends taking these into account in emissions modeling. The findings concerning active …