Under what condition can vehicles stop at a "No stopping during times shown except for as long as necessary to set down or pick up passengers" sign?

The correct choice indicates that vehicles can stop at a "No stopping during times shown except for as long as necessary to set down or pick up passengers" sign specifically to pick up or drop off passengers. This regulation is designed to facilitate the safe and efficient movement of passengers without causing additional congestion or hindrance to traffic.

The exception provided by the sign acknowledges that loading and unloading passengers is a necessary action, allowing drivers to stop for a brief period while ensuring that their vehicles do not block the roadway or violate traffic laws. This helps create a balance between the need for passenger transport and the smooth flow of traffic.

Other conditions, such as emergencies, maintaining traffic flow, or vehicle repairs, do not align with the specific exception granted by this sign, which is solely focused on the action of picking up or dropping off passengers.