Pollard, Justin (2008). "The Eccentric Engineer: The History of Traffic Lights Is Full of Twists and Turns". Engineering and Technology. 3 (15): 93. डीओआई:10.1049/et:20081518.
Hankscraft Inc. (11 October 2012). "Patent application title: Traffic Light Heater". Class name: Heating devices combined with diverse-type art device electrical devices, 20120255942. United States Patent Office. अभिगमन तिथि: 11 October 2012.