Which component is required for passenger vehicles to ensure safety on the road?

The required component for ensuring safety on the road in passenger vehicles is the rearview mirror. This safety feature is critical as it provides the driver with visibility of the area behind the vehicle, significantly aiding in safe lane changes, reversing maneuvers, and overall awareness of surrounding traffic. Proper use of the rearview mirror can help prevent accidents by allowing the driver to monitor conditions directly behind the car.

While other components like airbags enhance passenger safety during a collision and are indeed important, they are not required for a vehicle to operate legally on the road. The sunroof and leather seats, while contributing to comfort and aesthetics, do not play a role in safety. Therefore, the rearview mirror stands out as an essential safety feature mandated for passenger vehicles.