Traffic signal systems

Claim 1

A TRAFFIC CONTROL SYSTEM, INCLUDING A TRAFFIC SIGNAL UNIT HAVING AN INTERNAL SEQUENCING SWITCH AND A TIMER NORMALLY CONTROLLING SAID SEQUENCING SWITCH TO OPERATE THE TRAFFIC SIGNALS THROUGH A PREDETERMINED SEQUENCE OF PHASES, ACTUATING MEANS FOR ADVANCING SAID SEQUENCING SWITCH STEPWISE, EXTERNAL CONTROL MEANS FOR SAID ACTUATING MEANS, HOLD MEANS EXTERNALLY CONTROLLABLE FOR TRANSFERRING SAID SEQUENCING SWITCH FROM CONTROL BY SAID TIMER TO CONTROL BY SAID EXTERNAL CONTROL MEANS, AND A CENTRAL AUTOMATIC DIGITAL COMPUTER OF THE TYPE HAVING INPUT AND OUTPUT MEANS FOR DATA AND INSTRUCTIONS, MEANS FOR STORING OPERATIONAL INSTRUCTIONS AND DATA, AND MEANS FOR CARRYING OUT ARITHMETIC OPERATIONS AND LOGICAL OPERATIONS INCLUDING ACCESS TO THE STORING MEANS AND TO THE INPUT AND OUTPUT MEANS, A HOLD RELAY FOR CONTROLLING SAID HOLD MEANS AND AN INTERLOCK RELAY, EACH OF SAID RELAYS HAVING A HOLDING CIRCUIT AND HAVING RELATED CIRCUIT INTERRUPTING MEANS THAT ARE OPENED RESPECTIVELY DURING DIFFERENT PORTIONS OF EACH READ-OUT CYCLE OF SAID DIGITAL COMPUTER, SAID HOLDING CIRCUITS OF SAID RELAYS BEING EFECTIVE TO MAINTAIN THE RESPECTIVE RELAYS ENERGIZED, SUBJECT TO THE RELATED CIRCUIT INTERRUPTING MEANS REMAINING CLOSED, SAID DIGITAL COMPUTER BEING ADAPTED TO ENERGIZE SAID INTERLOCK RELAY MOMENTARILY DURING EACH READ-OUT CYCLE AND SAID INTERLOCK RELAY HAVING ITS HOLDING CIRCUIT IN SERIES WITH ITS RELATED CIRCUIT INTERRUPTING MEANS SO THAT SAID INTERLOCK RELAY IS DEENERGIZED ONCE IN EACH COMPUTER READ-OUT CYCLE, SAID INTERLOCK RELAY HAVING A FURTHER CONTROLLED CIRCUIT FOR HOLDING IN SAID HOLD RELAY WHEN THE INTERRUPTING MEANS RELATED TO SAID HOLD RELAY IS OPERATED, WHEREBY WHEN NO COMPUTER OUTPUT IMPULSES REACH SAID INTERLOCK RELAY IN ANY GIVEN READ-OUT CYCLE, SAID HOLD RELAY DROPS OUT AND RESTORES SAID ACTUATING MEANS TO CONTROL BY SAID TIMER.