Karl W. Berger, P.E.DCM, Inc.

Centreville, VA

IEEE/ASME National Capital Land Transportation CommitteeDecember 8, 2009

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.

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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

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.

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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.

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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.

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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)

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APPROACH8 – Used at interlockings.

Immediate Penalty 2 Emergency Brake on

Loss of Speed Code or Overspeed.

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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

April 2008 – broken wheel found on LRV

prior to entering service.

Fleet inspection found many wheels with

excessive damage and flats.

Investigation started.

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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.

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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%

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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.

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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.

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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.

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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.

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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.

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Wheel flatting eliminated.

Center Truck track brakes shoe life

reduced to 3 months.

ATP software modification added

discrimination and restored acceptable

shoe life.

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Improve dynamic brake slide control.

Improve friction brake slide control.

Replace car control computer.

Improve ATP integration.

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