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Human Reliability Analysis: Accounting for Human Error on Light Rail Transportation Systems

Human Reliability Analysis: Accounting for Human Error on Light Rail Transportation Systems. SYSM 6309 Advanced Requirements Engineering By: Michael Murphy. Agenda. Motivation Case Study Human Reliability Analysis (HRA) Tools Technique for Human Error Rate Prediction (THERP) Error Rates

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Human Reliability Analysis: Accounting for Human Error on Light Rail Transportation Systems

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  1. Human Reliability Analysis:Accounting for Human Error on Light Rail Transportation Systems SYSM 6309 Advanced Requirements Engineering By: Michael Murphy

  2. Agenda • Motivation • Case Study • Human Reliability Analysis (HRA) Tools • Technique for Human Error Rate Prediction (THERP) • Error Rates • Event Tree • Swiss Cheese Model • Possible Light Rail System Solutions • Questions

  3. Motivation • Federal Transit Administration’s (FTA) Office of Safety and Security compiled a report of light rail safety statistics from 2003 to 2008 that grouped light rail accident types with light rail accident causes. • 5 Types: Rail Grade Crossing (RGX) Collisions, Non-RGX Collisions, Derailments, Fire and Other • 4 Causes: Equipment Failure, Workforce Behavior, Customer Behavior and Public Behavior • Within that time span, there were 3,665 reported accidents. • Of the 3,665 reported accidents, 583 (16%) were caused by Workforce Behavior.

  4. Case Study: San Francisco Railroad Accident • Date: July 18, 2009 • Time: 2:50 pm, Pacific daylight time • Property Damage: $4.5 million • Injuries: 48 (28 serious) • Accident: L train 1433 struck the rear end of standing K train 1407 • K train was at the end (aka platform) of the West Portal Tunnel, waiting to merge onto the K line. • L train, controlled by automatic train control system (ATCS), pulled into tunnel. • L train operator “cut out” of ATCS to manually pull ahead to the platform. • L train was moving about 5 mph when the operator “blacked out” until impact.

  5. Accident Simulation Platform Tunnel Outbound K L K L KA-BLAM!!! Inbound K Train arrives in tunnel, no cars at platform. L Train arrives in tunnel, K Train still at platform. K Train pulls ahead to platform. L Train changes to manual and pulls ahead to platform.

  6. Cause of Accident • Human Error • L Train Operator failed to request permission of OCC management to disengage ATCS. • L Train Operator failed to keep the train in automatic mode until reaching the station stop at the West Portal platform. • Would have been a safe guard against his “black out” • OCC failure to monitor and enforce requirement that the operator wait until reaching the platform before changing operating mode of the train.

  7. Corrective Action • Bulletin issued reminding the train operators not to “cut out” of the ATCS without OCC permission. • The final sentence of the bulletin read, “Failure to comply with these existing rules outlined in the Rules and Instruction Handbook will result in discipline, up to and including termination.”

  8. Human Reliability Analysis (HRA) • Role is to provide the foundation for calculating the probability that the human element of an operator/process or system interaction will fail. • Majority of HRA methods were developed in the 1980’s due to concern caused by the accident at Three Mile Island.

  9. Technique for Human Error Rate Prediction (THERP) • Best known human performance reliability prediction technique which involves 5 steps: • Define the system or process. • Identify and list all human operations performed and their relationships to the system or process tasks and functions. • Predict error rates for each human operation or group of operations. • Determine the effect of human errors on the system or process -> Event Tree. • Develop and recommend changes that will reduce the system or process failure rate.

  10. Error Rates • Probability that a class of errors will lead to system failure is: Qi = 1 – (1 – FiPi)^nj • Error Rate Tables • http://panko.shidler.hawaii.edu/HumanErr/

  11. Event Tree

  12. Swiss Cheese Model

  13. Possible Light Rail System Improvements • Utilize THERP when building new or expanding current systems. • Additional training of established operating procedures. • Threat of disciplinary action when established operating procedures are not followed. • The German Aerospace Center has developed a Railway Collision Avoidance System (RCAS) • Safety overlay that can be deployed on top of any existing safety infrastructure in train networks. • Provides train position and vehicle dimensions to all other trains in the area using ad-hoc train-to-train communications.

  14. Questions?

  15. References • “Collision of Two Municipal Transportation Agency Light Rail Vehicles, 7/18/2009, San Francisco, CA,” http://www.ntsb.gov/investigations/reports.html • “Human Reliability,” http://en.wikipedia.org/wiki/Human_reliability • E. Hollnagel “Human Reliability Analysis,” 2002, http://www.ida.liu.se/~eriho/WhatIsHRA_M.htm • “Technique for Human Error Rate Prediction.” http://en.wikipedia.org/wiki/Technique_for_Human_Error_Rate_Prediction • Barbara Gregory, MPH, Victoria S. Kaprielian, MD “Anatomy of Error – Swiss Cheese Model,” http://patientsafetyed.duhs.duke.edu/module_e/swiss_cheese.html

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