When a transit agency uses FTA grant funds to procure rolling stock, Buy America rules require a minimum percentage of US-manufactured content and final assembly in the United States. Vehicles imported under 8603 for federally funded projects must comply with these requirements or obtain a waiver; vehicles procured without federal funding are not subject to Buy America but still face standard HTS duties.

The defining criterion is whether the vehicle has its own traction equipment. A self-propelled unit under 8603 can move under its own power; a non-self-propelled coach under 8605 must be hauled by a separate locomotive or traction unit. Articulated vehicles with distributed traction motors throughout the consist still classify under 8603 as long as the traction equipment is integral to the vehicle.