48 that uses the traffic signal power cable 50 to transmit the independent monitoring circuit state information the disconnect circuit 18 generally comprises a power transistor mosfet thus it is possible to drive the power transistor to create a high short circuit current and blow the fuse in series with the main circuit however during the proof test the disconnect circuit 18 is disabled in operation from time to time the ptc 14 simulates a faulty traffic signal state i e current equals zero or is below some threshold value to activate the independent monitoring circuit 10 without switching the traffic signal into a high impedance state that is the independent monitoring circuit 10 should not disconnect the fuse in series with the main circuit if the independent monitoring circuit 10 works properly the ptd 16 is energized and it communicates externally the current state of the independent monitoring circuit 10 the failure to communicate shall be considered a traffic signal failure and the traffic controller or the maintenance technician is thus notified and the traffic signal shall be immediately replaced the simulation test does not interfere with the overall functionality of the traffic signal there is no need to open the traffic signal in order to diagnose the independent monitoring circuit 10 the test can be done by periodical manual proof testing or on line testing the time.