An electronic message transmitted by radio between a Signal BoxThe building in which the Signaller(s) is/are situated together with the control and indication system for the signalling. See also Signalling Centre. and train.
It performs the function of a TokenAny Single Line Token, Staff or Tablet. but no physical TokenAny Single Line Token, Staff or Tablet. is required. See
RETBA Signalling System used mainly on Single Lines, where an Electronic Token is transmitted between the controlling Signal Box and train..