The director of public works may establish and maintain, by appropriate devices or marks, crosswalks at all intersections where there is particular danger to pedestrians crossing the roadway, and he may establish and maintain by signs, paint marks or other material, safety zones at any other places that require such safety zones. He may also mark traffic lanes upon the roadway where a regular alignment of traffic is necessary. Where such lanes have been marked or signs, marks or devices have been made or erected, it shall be unlawful for any operator to fail to keep his vehicle within the designated boundaries for vehicles. (1976 Code § 41.13)