Final answer:
The smoothest lanes on a highway with three or more lanes going in the same direction are usually the middle lanes.
Step-by-step explanation:
When there are three or more lanes going in the same direction on a highway, the smoothest lanes in terms of flow of traffic are usually the middle lanes. This is because the outermost lane (furthest from the median or center divider) is often used by slower-moving vehicles, such as trucks, and by vehicles entering or exiting the highway. The innermost lane (closest to the median) is often used by faster-moving vehicles who may be passing slower vehicles in the middle lanes.