An eastbound oil train has left CTC limits behind at Mesa and is now headed east in TWC (track warrant control) limits. So why is there a trackside signal? And an ever better question...why is the signal yellow when the train is in the block beyond the signal? The key is the "D" plate located on the signal mast near the bottom. That "D" plate indicates this is a "distant signal". This signal does not give any occupancy information about the block ahead. It only gives westbound trains an indication of the CTC signal at the east end of Mesa. Since that signal at East Mesa is currently red, this distant signal shows a yellow (Approach) indication. If the signal at East Mesa were green, this signal would also show a green. Even with something in the block immediately beyond the signal. Indeed, in TWC limits, there are no "blocks" per se.
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