According to the May 2018 version of the Canadian Rail Operating Rules (CROR), specific train horn warning signals must be sounded as per rule 14. Like the American railroad authority, signals are illustrated using "o" for short sounds, and "_______" for longer sounds. In the CROR, it states that warning signals "should be distinct, with intensity and duration proportionate to the distance the signal is to be conveyed". The following table lists the train horn warning signals required by Transport Canada. The signals marked with an asterisk (*) must not be replaced with radio communication.