JMRI : Cab Signals

JMRI generated Cab Signals are currently available for the following hardware types :

Signal Data Table Columns

JMRI Cab Signal Data Send Window

The table will attempt to identify which block the train is in via the block value ( train describer ).

The table will update when the train number is the block value.

A block initially has no direction set, forward values can only be calculated when JMRI knows what direction the block is set.

The direction is normally calculated by JMRI when a new block is occupied, then comparing neighbouring blocks.

This process can be triggered manually by clicking the Block Lookup button.

The button will change to a Reverse Direction button if a block is located for the train ID.

Layout Editor blocks can be checked for continuity in Layout Editor by taking the panel into edit mode, then clicking on Tools > Check.

You can view block routing by right clicking on an individual Layout Editor track segment and selecting View Block Routing.

The table will follow the block route of the train until it finds the next signal or bumper / buffer stop.

Signals used by this tool are defined using Aspect Signalling.

Digitrax Throttle Cab Signals

The LocoNet Cab signal indications is intended to work with Digitrax throttles with digitrax throttles that include semaphore icons for the Left and Right throttles. The code was developed and tested using a DT402 and a DT500. The basic message format shold work with a DT300 and DT400 as well, though they have not been tested by the author.

As of JMRI 4.15.4, it is only possible to send cab signal indications to throttles when they are plugged in to the LocoNet. This is limitation of the hardware and is true even on Duplex Wireless systems.

When a cab signal is active, The throttle will beep every time a new aspect is sent to the throttle. The beep may occur even when no change of aspect is seen.

The Digitrax Cab Signal Semaphores have 3 controlable blades (horizontal, diagonal, and verticle). When the semaphore is active, Each blade can be turned on and off. The semaphore can also be set to flash.

The JMRI support for Digitrax Cab Signal Semaphores uses the speed indication from the Aspects as indicated in the following table.

Aspect Mapping

Semaphore Appearance Mapped Signal Speeds Other Mappings
  • Clear
  • Normal
No matching speed was found, but the signal system indicates the aspect is permissive.
Flashing Vertical
  • Limited
  • Medium
No matching speed was found, but the signal system indicates the signal is neither a stop (danger) aspect or a permissive aspect
Flashing Diagonal This appearance is not currently used
  • Stop
No matching speed was found, but the signal system indicates the signal is a stop (danger) signal or the signal is held.
Flashing Horizontal
  • Restricting
  • RestrictedSlow
  • Restricted
  • Slow
Dot Indicates the cab signal is active, but no Aspect is currently available.
Nothing Indicates the cab signal is not active.


You can view this help page within JMRI by selecting Help > Window Help in the top bar of the Cab Signal window.

CBUS® is a registered trade mark of Dr Michael Bolton