Technical Reports

Risk Analyses for the IDOT Positive Train Control System to Determine Optimum Communications Timeout: Comparison to Cab Signal Systems with Continuous Train Stop and with Speed Control

  • 01
  • Nov
  • 2009
AUTHOR: Alan Bing, Ph.D.,* Eric Sherrock**
OFFICE: RPD
REPORT NUMBER: DOT/FRA/ORD-09/21
KEYWORDS: Positive train control, IDOT Corridor, Timeout, Latency, Risk Assessment
ABSTRACT: This project examines the influence of the communication timeout threshold and latency of a positive train control (PTC) system on its overall safety performance as compared with a cab signal system with continuous Automatic Train Stop and a fouraspect cab signal system with speed control, or an automatic train control system. The analysis was based on average daily traffic on the IDOT PTC corridor, which was composed of six passenger trains, between 0.86 and 1.07 PTC-equipped freight trains, and between 0.36 and 2.30 unequipped freight trains, depending on the season of the year. Maximum speeds considered were 110 miles per hour (mph) for passenger traffic and 60 mph for freight traffic. The latency values varied from 5 to 20 seconds (s) and timeout values varied from 20 to 360 s. Conclusions from this risk assessment are that for the traffic volume and traffic mix, the PTC latency and timeout in the ranges assumed in this study did not have a material effect on risk. Instead, nonsafety considerations such as route capacity, delay reduction, and cost may be the governing factors in the requirements for timeout and latency, instead of safety, for PTC communication network and design.

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