The DL&W, Erie and EL didn't use "Advance Approach." Where necessary for stopping distance, they used "Approach Medium" to an "Approach Signal." That was slightly ambiguous, because it was also used in the rear of a "Clear Medium" signal. But both instances called for the same response from the engineman at that point. "Clear Medium" was the Erie/DL&W/EL name for the indication more commonly called "Medium Clear." "Clear Medium" has a definite advantage, because when called across the cab of an engine, it is less likely to be mistaken for "Clear" if the first word is not heard.
Some DL&W colorlight signals had two arms with only three lamps, with red and yellow on the top arm and green on the bottom. They could display "Clear," "Approach Medium," "Approach" and "Stop" or "Stop and Proceed" depending on the presence or absence of a number plate. It might appear possible to display a "Clear Medium" on that signal, but that would never work because that same signal would also have to be able to display "Medium Approach" or "Restricting," where a yellow lamp was required in the bottom arm.
I disliked one factor on those DL&W signals. The absence of a light on the top arm upgraded the signal indication. A Yellow over Green was "Approach Medium," but a single Green on the bottom was "Clear." Same with a "Clear Medium," Red over Green. Our signal supervisor at Hoboken explained that the light-out relays always protected against such a false clear, but light-out relays don't detect snow, bird nests or branches obscuring the signal.
- Gordon Davids