Hines originated the concept of painting a line down the center of a road to separate traffic in opposing directions.[10] The idea came to him after watching a leaky milk wagon leave a trail down the street.[2] Painted center lines were first used in 1911 on River Road in Trenton, in Wayne County.[2] This simple idea has since been recognized as one of the most important single traffic safety devices in the history of highway transportation.[4][5] Snow removal from public roads was another of Hines' innovations.[5]