CBTC Explained - Train Positioning

In this video, I’ll walk you through the logic behind how CBTC determines train position, step by step.

0:00 - Intro
1:41 - Different train Localization methods
3:52 - How Train Localizes
5:50 - Building blocks
9:30 - Location update after crossing transponder (Odometry)
10:10 - Wheel Diameter Calibration
11:17 - Position Uncertainty
12:52 - Transponder Reading Error
13:34 - Transponder Installation Error
14:29 - Wheel Calibration Error
15:44 - Undetected Slip/Slide
18:07 - Discretization Error (Granularity and Quantization)
20:02 - Correcting with Tag Placement
21:02 - Secondary Speed Input (Speed Sensor/Accelerometer/Doppler Radar)


Please note: I’m only explaining the underlying principles and engineering logic. Actual CBTC implementations vary widely between suppliers and remain proprietary. The intent here is educational.

This video is part of an ongoing effort to build a comprehensive CBTC series, covering everything from train positioning and architecture to ATP/ATO/ATS, safety logic, and network design. My goal is to create a clear, systematic reference for anyone interested in understanding how CBTC really works.

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