Railway Wiki

• 1: Glossary
• 2: ETCS (ERTMS)
• 2.1: ETCS

1 - Glossary

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2 - ETCS (ERTMS)

2.1 - ETCS

Context

The onboard computer of ETCS-enabled trains has to compute a number of position / speed curves. Here is how it works:

• below all the curves, the speed indicator is white
• above the indication curve, the speed indicator is yellow
• above the permitted curve, the speed indicator is orange
• above the warning curve, an alarm rings
• above the intervention curves, an emergency break intervention is triggered

Inputs

In order to compute any of these curves, a number of things are needed:

• target data (the destination of the braking curve, which can be EOA and SvL or LOA and MRSP)
• train data
• infrastructure data
• infrastructure manager constants
• standardized constants

Train

• max speed
• length
• rotating mass
• T_traction_cutoff: the time it take to cut off traction
• braking model, either lambda or gamma:
  • lambda (braking weight/mass)
  • gamma (constant deceleration at a given speed)
• correction factors (k_dry and k_wet for gamma braking) for braking curves

Infrastructure

• corrected gradients (it incorporates curvature)
• odometry balise locations

Processes

Braking coefficients:

• A_brake_emergency is the expected emergency braking capability, without safety margins
• A_brake_safe is the emergency braking coefficient, with safety margins
• A_brake_service is the expected service braking capability, without safety margins

Speed / distance targets

• EOA end of movement authority: the location until which the train is allowed to move
• SvL supervised location: the protected location

Curves

• SBD supervised braking deceleration: intermediary result computed from EOA and A_brake_service
• EBD emergency braking deceleration: intermediary result computed from SvL and A_brake_safe

All the curves below are cut below a given release speed:

• EBI (emergency break intervention) computed from EBD, shifted in position and space given rolling stock metadata
• SBI1 computed from SBD, shifted in time with Tbs1
• SBI2 computed from SBD, shifted in time with Tbs2
• FLOI (also called SBI, the intervention curve) the minimum of SBI1 and SBI2
• WARNING (warning curve) computed as a shift of FLOI by Twarning
• PS (permitted speed curve): shift of WARNING by time Tdriver
• INDICATION is a shift of PS by time Tindication