If the tractor is designed for propulsion by both a compression-ignition engine and an electric motor simultaneously or alternatively, it classifies under 870122, not 870121. The presence of an electric drive motor for propulsion — even if the diesel engine is the primary power source — is the distinguishing criterion. Tractors where the electric motor serves only auxiliary functions (e.g., powering accessories) without contributing to propulsion may still fall under 870121; a technical specification review is essential.

Yes. Hybrid semi-tractors must meet EPA greenhouse gas and criteria pollutant emission standards applicable to heavy-duty vehicles, which may differ from the standards in the country of manufacture. DOT Federal Motor Vehicle Safety Standards (FMVSS) also apply. Importers should obtain a conformance statement from the manufacturer and, for used units, verify that the vehicle was originally certified to US standards or has been brought into compliance before entry.