Final answer:
Turn signals are legally required, and drivers must use them to indicate a change in direction, even if no other vehicles appear to be in sight.
Step-by-step explanation:
The correct answer to the question is that turn signals are mandatory by law. It is legally required for drivers to use turn signals to indicate when they are making a turn or changing lanes.
This is a safety measure to inform other drivers and pedestrians of a vehicle's intended direction of travel. Despite the importance of turn signals, there are studies suggesting a significant portion of drivers do not use them consistently or correctly.
However, even if there are no other vehicles visible, the law still requires a signal to be given as others may not be readily apparent, such as cyclists or pedestrians that could be in harm's way.