Frequencies listed here are used for train status within the train. EOTD's (End Of Train Device), also known as FRED's (Flashing Rear End Device) are fixed at the rear of most freight trains. This device is linked to the HOTD (Head Of Train Device) also known as a MARY (as opposed to "FRED"). The devices report that the train is moving, air pressure and emergency status of the air valve along with its specific radio ID. This data burst is commonly used by the railfan community that a train is in the listener vicinity. Trains using DP or Distributive Power (remotely controlled locomotives) also use 450MHz frequencies to control such locomotives and transmit information such as power or brake setting, unit ID and other status information. Remote Controlled Locomotives (RCL) are typically found in yards/terminals on yard jobs. Some may be found on mainlines on local jobs but are not used for through trains and are not the same as DP locomotives.