What function must the turn signal perform, even though it isn't required to automatically cancel?

The correct function that a turn signal must perform is to lock into proper turning positions. This means that when a driver activates the turn signal, it should remain in the "on" position until the driver manually cancels it by returning the signal lever to its original position. Ensuring that the turn signal stays activated until the driver completes the turn is essential for clear communication to other drivers about the intended direction of the vehicle, promoting safety on the road.

In this context, the other options do not adequately apply to the function of turn signals. The requirement is not for the turn signal to shake at a specific frequency or flash continuously; rather, it’s about its visibility and indication purpose. Additionally, turn signals do not need to change color when activated, as their primary function is to signal intentions through a consistent color—amber or yellow is the standard in the U.S. This consistency aids in maintaining universal understanding among drivers regarding a vehicle's movements.