What do double yellow lines that are both solid indicate?

Double yellow lines that are both solid indicate that crossing them to pass another vehicle is prohibited, with the exception of making a left turn when it is safe to do so. This regulation is designed to ensure safety on the road, as solid double lines are used in areas where visibility may be limited or where passing could be hazardous. Therefore, drivers should not attempt to change lanes or overtake other vehicles in these areas, except when turning left at intersections or driveways when it is safe to do so. This understanding helps maintain orderly traffic flow and reduces the risk of accidents.