What is required for a safe distance when driving at higher speeds?

When driving at higher speeds, it is essential to maintain a following distance that exceeds the stopping distance. The stopping distance refers to the total distance a vehicle travels from the moment the driver perceives a need to stop until the vehicle comes to a complete stop. This distance increases with speed due to factors like greater momentum and longer reaction times.

Maintaining a distance longer than the stopping distance ensures that the driver has adequate space to react to sudden emergencies or obstacles. It provides a buffer that can absorb any unexpected events without compromising vehicle control or safety.

In contrast, the other options do not guarantee safety at higher speeds. For example, having only 0.5 seconds of reaction time may not be sufficient due to the increased speed, which can dramatically extend the actual stopping distance needed. Similarly, while clear visibility ahead is crucial for safe driving, it does not directly address the specific requirement for maintaining a safe distance based on speed and stopping capability. The suggestion of two times the vehicle's length may not correspond correctly to the increased stopping distance needed at higher speeds.

Ultimately, maintaining a distance that is longer than the stopping distance takes into account all the necessary factors for safe driving under demanding conditions.