What characterizes a divided highway?

A divided highway is characterized by the presence of a median in the roadway, which serves to separate opposing lanes of traffic. This median can be composed of various types of physical barriers such as concrete walls, grass, or simply a wide space, and is designed to enhance safety by minimizing the risk of head-on collisions. The division allows vehicles traveling in opposite directions to operate separately, increasing overall traffic flow and providing a clearer and safer environment for drivers.

The other options do not accurately define a divided highway; for instance, a single lane of traffic does not imply division, traffic lights may not be present on all types of highways, and road signs placed every mile do not characterize the specific structure or layout of a divided highway. These elements might be features of various roads but do not define what constitutes a divided highway specifically.