BART DEMONSTRATION REPORT

ACCORDING TO THE GENERAL RAILWAY SIGNAL SYSTEM, SEPARATION OF TRAINS IS MAINTAINED BY A DISCRETE BLOCK SYSTEM. AUDIO-FREQUENCY SIGNALS ARE INJECTED INTO THE RAILS AT INTERVALS EQUAL TO THE DISTANCE WITHIN WHICH A TRAIN CAN STOP FROM THE SPEED LIMIT ENFORCED BY THE SIGNAL SYSTEM. IN THE SIMPLEST ARRANGEMENT, TWO FREQUENCIES ARE USED WHICH ARE APPLIED AT ALTERNATE LOCATIONS. RECEIVERS ON EACH TRAIN SENSE THE PRESENCE OF SIGNALS IN THE RAILS. THE WAYSIDE LOCATIONS ARE NORMALLY DEENERGIZED EXCEPT FOR THE TWO IMMEDIATELY AHEAD OF A TRAIN. THUS, THE TRAIN RECEIVES TWO FREQUENCIES WHEN THE BLACK AHEAD IS UNOCCUPIED. UNDER THESE CONDITIONS, THE TRAIN PROCEEDS AT AN AUTHORIZED SPEED. THE SHUNTING ACTION OF A TRAIN IN A BLOCK PREVENTS THE SIGNAL IN THE RAILS FROM APPEARING BEHIND THE TRAIN. THUS, IN A BLOCK BEHIND AN OCCUPIED ONE, THERE CAN BE ONLY ONE SIGNAL. A TRAIN ENTERING A NEW BLOCK RECEIVES ONLY ONE SIGNAL; THUS THE TRAIN PROTECTION SYSTEM APPLIES THE BRAKES AND THE TRAIN IS STOPPED SHORT OF THE ENTRANCE TO THE NEXT BLOCK. THE DETECTION OF CLEARANCE IS ACCOMPLISHED DIRECTLY BY THE CAR- CARRIED EQUIPMENT. TO TRANSMIT COMMANDS TO THE TRAIN FOR ENFORCING SPEED LIMITS, THE SIGNAL INJECTED AT THE LOCATION IMMEDIATELY AHEAD OF A TRAIN IS FREQUENCY-MODULATED BY PAIRS OF LOW FREQUENCY TONES, ONE PAIR BEING USED FOR EACH SPEED LIMIT. THE AUTHORS HAVE CONCLUDED THAT THE WAYSIDE LINE SUPERVISION SYSTEMS ARE REALIZABLE. THEY FOUND THE CROSS-TALK BETWEEN TRACKS CAN BE KEPT AT ACCEPTABLY LOW LIMITS PROVIDED THAT THE TRACK RAILS ARE BALANCED TO GROUND. NEITHER THE D-C NOR A-C PROPULSION SYSTEM INTERFERE WITH THE RECEPTION OF TRACK SIGNALS. THE FIXED BLOCK SYSTEM PROVIDES A HIGH DEGREE OF INHERENT DAMPING IN THAT ONCE A TRAIN SLOWS DOWN BECAUSE OF APPROACHING TOO CLOSELY TO A PRECEDING TRAIN, ITS HEADWAY REVERTS TO A NON-INTERFERING LEVEL, PROVIDED THE LEAD TRAIN MAINTAINS ITS SCHEDULED SPEED. /UMTA/

  • Supplemental Notes:
    • PROJ NO CAL-MTD-2
  • Corporate Authors:

    General Railway Signal Co

    ,    
  • Publication Date: 1966-6

Subject/Index Terms

Filing Info

  • Accession Number: 00241776
  • Record Type: Publication
  • Source Agency: Urban Mass Transportation Administration
  • Files: TRIS, USDOT
  • Created Date: Feb 3 1973 12:00AM