What does a solid white line on the right edge of the road indicate?

A solid white line on the right edge of the road is the 'fog line' that marks the right edge of the traveled roadway. To its right is the shoulder, which is for emergency stopping, not normal travel. Crossing the fog line consistently is a sign of driver fatigue or distraction. Fog lines also help drivers stay in their lane in fog, snow, or at night when visibility is reduced. Some highways have audible 'rumble strips' along the fog line that make a loud noise if a tire crosses, alerting a drowsy driver before they leave the road. Crossing the fog line to pass slower traffic on the right is generally illegal and unsafe.