Final answer:
A single broken white line on a multi-lane highway indicates that lane changes are allowed. Drivers should change lanes carefully, adhering to the speed limit and traffic conditions.
Step-by-step explanation:
On a multi-lane highway, a single broken white line indicates that vehicles are permitted to change lanes, but they should do so with caution. These lines serve to separate lanes of traffic moving in the same direction, and drivers should ensure it is safe to change lanes by checking for other vehicles and using their indicators before making the maneuver. However, it's important for drivers to be aware of their surroundings and obey the posted speed limit, even when changing lanes, to maintain safety on the highway.