Complex sentence: With modern radios such as CSR and GSM-R it is not even necessary for the driver to speak to the signaller: pressing the "SG" button on the train's radio will send a "Train standing at signal" message.
Split into simpler sentences: With modern radios such as CSR and GSM-R it is not even necessary for the driver to speak to the signaller. Pressing the "SG" button on the train's radio will send a "Train standing at signal" message.