Final answer:
The center line used to mark the center where there are only two lanes of traffic is a broken line. This line can be crossed when it is safe to turn or pass another vehicle.
Step-by-step explanation:
When there are only two lanes of traffic, the center line used to mark the center is a broken line. This type of center line indicates that it is safe to cross the line to turn or pass another vehicle when it is safe to do so. The broken line allows for flexibility and provides drivers with the opportunity to make necessary maneuvers.
For example, if a driver wants to turn left onto a side street, they can cross the broken center line when it is safe to do so. Similarly, if a driver wants to pass a slower vehicle, they can also cross the broken center line when it is safe.