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Highlights • Field and simulated car-following trajectories were compared in the Wiedemann Cartesian systems. • The existence of the regime structure led to the "acceleration cliffs". • The "acceleration cliffs" were found to be responsible for the unrealistic VSP distributions. • The "acceleration cliffs" could be eliminated by implementing continuous acceleration models. Abstract Errors have been found in the speed-specific vehicle specific power (VSP) distributions generated by the Wiedemann car-following model. The impact of the existence of the regime structure on the distributions was investigated in this paper. The analysis was conducted based on massive field car-following trajectories and numerical simulation of the Wiedemann model. The field and simulated speed-specific VSP distributions and acceleration distributions were compared. The field and simulated accelerations were analyzed with the help of the Wiedemann Cartesian systems. The unrealistic "acceleration cliffs" were found along with the regime borders. It was indicated that the "acceleration cliff" was a source of the generated emission errors. The existence of the discrete regimes was responsible for the "acceleration cliff." It was indicated that the "acceleration cliff" could not be eradicated by the parameter calibration, unless the logics of the regimes were modified. A data-driven model was designed based on the Wiedemann plane. The "acceleration cliffs" were successfully eliminated by implementing continuous accelerations. It was indicated that the Wiedemann model had the potential to generate realistic VSP distributions. [ABSTRACT FROM AUTHOR]

Incorporating cold-start emissions from hybrid electric vehicles (HEVs) into on-road emission modeling is fundamental to accurately assess the environmental impacts aligned with their projected deployment. This study introduces a cold-start emission model, integrating travel time, dynamic emission rates, and cold-start durations by fuel type. This study further explores the anticipated spatiotemporal patterns of annual cold-start emissions. Findings indicate a reliance on gasoline for most on-road vehicles in the next decade, but vehicle electrification could reduce carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NO X) emissions by over 60% by 2035. Cold-start emissions will remain significant (67%-79% of CO, 59%-71% of HC, and 42%-54% of NO X emissions), especially on local roads. Cold-start emissions from HEVs will contribute to 14%, 25%, and 13% of total CO, HC, and NO X emissions in 2035, respectively. This study highlights the importance of accurate modeling in understanding the environmental benefits of vehicle electrification. [ABSTRACT FROM AUTHOR]