Final answer:
Double reflectors are used to outline objects on freeways. These corner reflectors consist of two reflecting surfaces that reflect light back parallel to the direction from which it came. They are commonly used on bicycles, cars, and warning signs to provide visibility and safety.
Step-by-step explanation:
Double reflectors are used to outline objects on freeways. These reflectors, also known as corner reflectors, consist of two mutually perpendicular reflecting surfaces that reflect light back exactly parallel to the direction from which it came. They are commonly used on bicycles, cars, warning signs, and even the moon's surface to provide visibility and safety.