Weaving configuration, as one of principle freeway geometric variables, has a significant effect on the quality of weaving operations, and thus may impact vehicle emissions. This paper quantitatively investigates the impact of different weaving configurations on emissions in order to assess the air quality implications in designing weaving configurations. Most existent weaving segments are one-sided, e.g. on-ramp and off-ramp are located on the same side of the freeway. Ramp-weave and major-weave, as the most commonly used one-sided configurations, are selected as the object of study. The studied configurations are modeled in VISSIM which, in this study, is applied to generate instantaneous speed and acceleration profiles for developing operating mode distributions. The characteristics of operating mode distributions resulting from each configuration are examined to identify the factors that result in the differences in emissions. The study demonstrates that braking, idling, and low speed coasting/acceleration produce higher emissions, while moderate speed coasting/acceleration as well as high-speed acceleration are triggers of lower emissions. The weaving ratio, volume ratio and the distribution of weaving flow between freeway-to-ramp and ramp-to-freeway are critical factors that have a significant impact on emissions production for each weaving segment. In addition the simulation runs were tested in the INTEGRATION software in order to validate the results. The study demonstrates the consistency between the INTEGRATION and VISSIM simulations. Additionally, the results from INTEGRATION demonstrate that the origin-destination demand level may be a significant indicator in deciding which configuration is environmentally best.