Vehicles turning left at intersections from opposing left-turn lanes often restrict each other’s sight distance. Previous research has developed guidelines for offsetting opposing left-turn lanes to provide adequate sight distances. Implementation of these guidelines at existing intersections typically involves reconstructing the left-turn lanes. However, increasing the width of the lane lines between left-turn lanes and the adjacent through lanes has also been found to improve the sight distance between opposing left-turn lanes. Using the relationship found between lane-line width and available sight distance, guidelines for designing the width of left-turn lane lines to provide the required sight distance for opposing left-turning vehicles are presented.