Centerline markings are painted lines on roadways that indicate the center of the lane. They help drivers stay in their lanes and provide guidance for safe passing. These markings can be solid or dashed, with solid lines indicating no passing and dashed lines allowing for passing when safe. These markings are essential for road safety and are part of traffic control devices regulated by organizations like the Federal Highway Administration. Proper visibility and maintenance of centerline markings are crucial for preventing accidents and ensuring smooth traffic flow.