outdoor sections, yellow and green flags are also used for the same purpose. A flashing blue light at track level indicates workers may be present, subway operators are required to sound their horn, and follow the signals of track workers when approaching and passing them. See also 1995 Russell Hill subway accident New York City Subway signaling Railway signalling References External links SIGNALS: Questions and Answers about the Signals in use by the Toronto Transit Commission (PDF Format). Transit Toronto. TTC's Signal System Explained on YouTube, published by the TTC on March 5, 2014 How the Toronto (TTC) Subway Train Signal System Works on YouTube, published by T2P Films on June 23, 2014 This article explains the old block signal system and the new communications-based train control (CBTC) to be implemented on Line 1 between 2017 and 2019. , published by The Globe and Mail on June 7, 2017 Toronto rapid transit Railway signaling in Canada Train protection systems