Under what condition are U-turns legal in residential districts?

U-turns are generally legal in residential districts when there are no oncoming cars present. This condition ensures that the maneuver can be completed safely without risking a collision with approaching vehicles, as U-turns can take up more space and require the driver to navigate across lanes. The absence of oncoming traffic reduces the potential for accidents, allowing drivers to execute the turn more safely.

The other options presented highlight situations that may not necessarily align with safe U-turn practices. For instance, being at a stop sign does not inherently grant legality to a U-turn, as stop signs are typically meant to control traffic and prioritize safety. Similarly, while a clear street free of pedestrians is important for overall safety, it does not address the crucial factor of oncoming traffic. Lastly, the speed limit being 25 mph or lower does not automatically make U-turns permissible; it primarily indicates the maximum speed allowed rather than specific conditions related to traffic or road layout. Thus, the safety consideration of ensuring no oncoming cars is the key factor that makes U-turns legal in residential districts.