High emitters represent a small fraction of the vehicle fleet, yet they are responsible for a large portion of the total mobile source emissions. Drive-cycle-specific high-emitter cut points for the identification of high-emitter vehicles are first developed. A microscopic model for estimating high-emitter vehicle emissions by using second-by-second emission data is developed subsequently. The proposed model estimates vehicle emissions with a margin of error of 10% when compared with in-laboratory bag emission measurements. The model was incorporated in the INTEGRATION traffic assignment and simulation software for the environmental assessment of alternative traffic operational projects, including emerging intelligent transportation system initiatives.