* T3 keeps passengers in railroad cars safe. * In those places in which radio environment is weak and wire announcement is not allowed (such as in a subway and in a train) * Wireless announcement becomes possible by using the radio relay system with low power in case of emergency situation. * T3 is the solution for wireless announcement * T3 is the system that makes an announcement to passengers even if the power is cut off in case of emergency. * It is because devices with built in rechargeable batteries are installed in railroad cars and voice packet is relayed for receiving & transmitting by the digital wireless relay method of installed devices.