A Review of the Department of Transportation Plan for Analyzing and Testing Electronically Controlled Pneumatic Brakes (2017) / Chapter Skim
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A Review of the Department of Transportation Plan for Analyzing and Testing Electronically Controlled Pneumatic Brakes Letter Report A Report of
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i National Academies of Sciences, Engineering, and Medicine Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 February 17, 2017 The Honorable Elaine Chao Secretary U.S. Department of Transportation 1200 New Jersey Ave, SE Washington, DC 20590 Dear Secretary Chao: In response to a congressional request, the National Academies of Sciences, Engineering, and Medicine (NASEM)
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ii ECP Brake Force Propagation in Emergency Applications The DOT modeling approach for the HHFT final rule includes no delay in the emergency application of ECP brakes in response to a derailment. All train cars are assumed to initiate emergency braking at the beginning of the simulation; a latency time for detecting loss of brake pipe pressure and for signals to be received at all cars to initiate emergency braking was not included in the modeling.
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iii Contents ABBREVIATIONS..................................................................................................................................................
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v Abbreviations AAR Association of American Railroads ABDX Current air brake valve manufactured by Wabtec ADF average derailment/collision blockage force BC brake cylinder BCP brake cylinder pressure BP brake pipe or train line BPP brake pipe pressure CAWG Collision Analysis Working Group CCD car control device DB-60 Current air brake valve manufactured by New York Air Brake DOT U.S. Department of Transportation DP distributed power ECP electronically controlled pneumatic EOT end-of-train device FAST Act Fixing America's Surface Transportation Act fps feet per second FRA Federal Railroad Administration GAO U.S.
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vi TTCI Transportation Technology Center, Inc. UMLER Universal Machine Language Equipment Register Wabtec Westinghouse Air Brake Technologies Corporation WDP wired distributed power DEFINITION OF KEY TERMS Emergency braking Application of maximum braking force to stop a train as quickly as possible.
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1 LETTER REPORT ON A REVIEW OF THE DEPARTMENT OF TRANSPORTATION PLAN FOR ANALYZING AND TESTING ELECTRONICALLY CONTROLLED PNEUMATIC BRAKES INTRODUCTION In May 2015, the U.S. Department of Transportation's (DOT's)
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2 ECP brake systems simultaneously send an electronic braking command to all equipped cars in the train. All cars and controlling locomotives in the train must be ECP equipped for the ECP brake system to work.
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3 an increase in the average number of service interruptions per trip for trains with ECP braking systems as opposed to other braking systems. ECP communication issues, such as intercar connector reliability, were among the factors mentioned.7 As a result, whether the safety evidence was sufficient to justify the ECP brakes requirement was questioned.
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4 ment scenarios examined. The approach used in the study conducted by AAR estimated the total energy dissipated in the derailment and the number of cars reaching the POD instead of the number of cars punctured.
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5 Pneumatic Brakes Components of the modern pneumatic brake system on each car include a reservoir for compressed air, a brake valve, and a BC (see Figure 1)
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6 Symbol definitions: FIGURE 2 Brakes released. Piston in BC is fully retracted due to the contained spring.
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7 ECP Brakes ECP brakes are set or released by a signal sent through an electric line connecting all the cars in a train to the locomotives instead of relying on a pneumatic signal through the BP (see Figure 4)
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8 The EOT device at the rear of the train communicates with the HOT component to indicate the status of the BPP and that the device is in motion. If the EOT device at the rear detects a drop in the BPP, the EOT device sends a signal to the HOT device.
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9 the train in emergency mode, or it can be programmed to notify the engineer, who decides whether to initiate emergency braking. • The closer the POD is to the head of the train, the more effective the brake application will be on the portion of the train trailing the POD, relative to pneumatic braking alone.
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10 common ECP communication system and are received by all cars and locomotives on the ECP network at the same time.19 • For an emergency brake application caused by an air hose separation, an ECP-only system initiates an emergency brake application when two or more CCDs detect the drop in BPP below 50 psig. A message from the CCDs is automatically sent down the ECP electric line setting brakes in emergency application simultaneously on the other cars.
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11 comparing ECP and pneumatic brakes, Figure F-6 (Appendix F) indicates that for pneumatic brakes, the BCP began to develop within the first second.
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12 Several simplifying assumptions were made when the LS-DYNA model was developed. The track was not explicitly modeled but was simulated as level and tangent.
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13 (RAIRS) database.
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14 energy dissipated in the derailment. These reaction forces or blockage forces are propagated through all the cars on the track, from car to car through the draft gear and couplers.
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15 Finally, a parametric study was conducted to evaluate the effect of a range of values for train speed, derailment points within a train, track grade, and brake systems (including placement of the DP within the train) on stopping time and distance for each scenario.
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16 brake for the ECP system versus the pneumatic system is reduced to one to two cars. In subsequent analyses, NTSB varied the NBR in addition to the parameters that were evaluated in the AAR study.
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17 braking event up to the POD. The AAR analysis determined these forces by using TOES; the NTSB analysis used TEDS.
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18 gravel mixture, single size hard rock fill" is reported as 0.30 with other factors varying between 0.2 and 0.4 (page 68 of Final RIA, May 2015)
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19 TABLE 2 Comparison of Modeling Methods and Results Modeling Aspect DOT–Sharma AAR NTSB On-track modeling Sharma model TOES TEDS Discrete model for each car on the track Yes Yes Yes Discrete model for each derailed car off the track Yes No No Braking forces included Yes Yes Yes Evaluated EOT and DP separately No Yes No Forces for individual derailed cars included Yes No No Car-to-car collision forces included Yes No No Forces for aggregate of derailed cars included Yesa Yes Yes Use of parametric study to evaluate additional parameters No Yes Yes Puncture probability calculated Yes No No a Through a complete simulation of the pileup dynamics, the blockage force is fully accounted for. Car-to-Car Contact Forces In the DOT–Sharma approach the motion of all the cars is modeled by using LS-DYNA3D, as stated in the Sharma report: "The cars were individually modeled in three dimensions (3-D)
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