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Light Rail Braking & Automatic Train Protection


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Light Rail Braking & Automatic Train Protection

  1. 1. Karl W. Berger, P.E. DCM, Inc. Centreville, VA IEEE/ASME National Capital Land Transportation Committee December 8, 2009
  2. 2. Long term inadequate inspection allowed fleet-wide wheel defects. Investigation revealed underlying problem caused by poor integration of car braking systems with Automatic Train Protection (ATP). A temporary fix completely eliminated wheel damage. 2
  3. 3. Opened in 1992 as a single-track line. Central Line + 2 branches = 30 miles. Serves 33,600 passengers per day. 53 large LRVs by ABB (Bombardier). Originally equipped with Automatic Block Signals (ABS) and magnetic Trip Stops. Several collisions revealed deficiencies with Trip Stops. 3
  4. 4. Progressively upgraded Central Line between 2004 and 2006. Replaced ABS with Cab Signaling with Automatic Train Protection. Removed wayside signals and trip stops. Reduced headways from 17 minutes to 8 minutes. Improved service reliability. 4
  5. 5.  Wayside signal system impresses each track block with a speed codes.  Speed code inductively coupled to lead vehicle in train.  Operator normally controls train below received speed code.  Audible alert if operator exceeds speed.  Automatic Train Protection applies brakes if operator or vehicle fails to respond. 5
  6. 6. Guaranteed Emergency Brake Rate (GEBR) of 1.5mphps (0.67 m/s2) implemented with vital systems. GEBR achieved with single-point failures in braking systems. Signal block lengths designed to include adjustment for grade and curvature. 6
  7. 7. Condition Cab Signal Command LRV Response Speed < Speed Code – 1.5 mph Normal Operate Normally Speed = Speed Code – 1.5 mph Propulsion Disable Inhibit Propulsion Speed > Speed Code + 0.5 mph Penalty 1 (Overspeed) Apply Full Service Braking Penalty 1 Active AND Decel < 1.5 mphps for > 3 seconds Penalty 2 (Brake Assurance) Apply Emergency Brakes (vital) 7
  8. 8. APPROACH8 – Used at interlockings. Immediate Penalty 2 Emergency Brake on Loss of Speed Code or Overspeed. 8
  9. 9. Constraints due to nearly obsolete car control computer. Added redundancy to remove single-point failures in friction and track brake systems. Added two emergency magnet valves for ATP Emergency Brake applications. 9
  10. 10. April 2008 – broken wheel found on LRV prior to entering service. Fleet inspection found many wheels with excessive damage and flats. Investigation started. 10
  11. 11. The fall leaf season intensified the problem. Northern half of system shut down in early November 2008. Only 7 cars operational by mid-November. Intensified research into problem and solutions. 11
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  13. 13. Causes: • Inadequate slide control in service braking • No slide control in Emergency Braking • Problems induced by other defects. Distribution: • Brake Assurance – General 36% • Brake Assurance – Greasy Rail 22% • APPROACH8 anomaly 21% • Unknown/Unaccounted 14% • Operator commanded 7% 13
  14. 14. Component failures in signal cabins caused momentary loss of speed code at interlockings. (APPROCH8 Anomaly) Excessive grease on curves reduced adhesions. Accounted for 43% of Emergency Brake flats. 14
  15. 15. Inadequate slide control in service braking – typically 0.8 to 1.2 mphps during slide. No slide control in Emergency Braking. Higher adhesion demand on unpowered center trucks. Maintenance was not refilling sand boxes. 15
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  17. 17. LRVs equipped with six electromagnetic track brakes (one pair per truck) . Each pair provides ≈ 0.8 mphps. Sliding wheels + Track Brakes > 1.5mphps Not fail safe – power required for actuation. Cannot be used to meet GEBR. 17
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  19. 19. Energize one pair of track brakes on ATP overspeed (Penalty 1). Track brakes add ≈0.8 mphps to full service brakes. GEBR satisfied with sliding wheels. Vitality provided by existing Emergency Brake response. 19
  20. 20. Added two diodes and an On/Off switch. Effectiveness verified by test. Vitality of ATP confirmed by Failure Mode Effects and Criticality Analysis. Entire fleet retrofitted and tested in one week. Full service over entire system restored by the end of November 2008. 20
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  22. 22. Wheel flatting eliminated. Center Truck track brakes shoe life reduced to 3 months. ATP software modification added discrimination and restored acceptable shoe life. 22
  23. 23. Improve dynamic brake slide control. Improve friction brake slide control. Replace car control computer. Improve ATP integration. 23
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