For interstate driving, slow-moving vehicles must travel _________, except when passing.

Answer: B — On the rightmost lane

For interstate driving, slow-moving vehicles are required to travel in the rightmost lane, except when passing. This regulation helps maintain smooth traffic flow and ensures that faster-moving vehicles can pass without hindrance. The right lane is designated for slower traffic, allowing speedier vehicles to use the other lanes for overtaking. This lane-specific rule promotes safety and reduces the risk of collisions caused by faster vehicles unexpectedly encountering slower traffic in the left or middle lanes. By keeping slow-moving vehicles in the rightmost lane, it provides a predictable path for all drivers and minimizes the chances of traffic bottlenecks or accidents. This practice is particularly important on highways where speeds can be significantly higher, and compliance with lane usage rules is critical for overall traffic harmony.