In the bi-polar mess that are Union Pacific Signal rules, an often overlooked feature are the < C > plates that upgrade Advance Approach and Diverging Advance Approach to Advance Approach [Commuter] and Diverging Advance Approach [Commuter]. These modifiers came about in association with the Caltrans funded Capitol Corridor service between Sacramento and San Jose and upgrade the speed restriction associated with an Advance Approach signal indication to 60mph from 40mph.While this falls way short of the 90-110mph operation and 60-80mph high speed turnouts the line should have, its at least a step to improve performance.
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| SP vintage mast signals displaying Advance Approach with a < C > Modifier |
Anyway, at some point between 2023 and 2024, [ C ] markers appeared on virtually all signals on the Caltrain main line. While I am still waiting on rulebook confirmation, it seems likely that Caltrain is trying to take full advantage out of the performance of its new electric trains. With short signal blocks of 1 mile or less, Caltrain makes use of 4 or 5 block speed signaling to keep trains moving. Caltrain already defined Limited Speed as 50mph vs the more typical 40 or 45mph, but the new [ C ] plates will boost the speed of following movements from 50 to 60mph where an unrestricted speed if normally 80mph.
While I was initially concerned that Caltrain was dumping its unique speed signal system for standard Union Pacific rules, this does not seem to be the case. However it is still possible that some of the signal progressions may have changed such a replacing Approach Limited -> Approach with Advance Approach -> Approach. For reference, here is how the same location looked in 2017 before the [ C ] boards were applied.
If any readers in the bay are on Caltrain in peak periods, consider checking the speed after the trains pass an advance approach and let me know what you find in the comments.
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