BoundedApproachNaming

Geographic Approach Block Naming Versus "Bounded"

(Credit to Mark Landgraf for the term "Bounded".)

Some of us old heads still stick with something called bounded approach block naming, and this is an attempt to explain why. Going back to the left-right convention, there was one logical way to associate an approach track with a signal. If your signal name was RG, then the track in approach to this signal was RA. No directional component was involved in this type of naming. This is not to say that some railroads didn't do things differently. Perhaps the approach blocks names or numbers had no correlation to any signal name. But from what most older signal prints show, this was pretty common. Using my old tutorial's stick diagrams, here is a sample of that scheme:

                              O-  A:LG/NW
A:RA________________(TK)___________________A:1LA
              A:NW \          O-  A:LG/RW
      A:RG  -O      \______________________A:2LA

This also had the effect of setting of a precedent for naming an approach track for the signal it led up to. And it was not exclusive to block signaling. Even in crossing protection, some railroads like the Illinois Central would name approach tracks to flasher-protected crossings based on the concept of direction "bound", for example SBAT for South Bound Approach Track. New York Central, however, named approach tracks by their geographic locations, like WT for West Track and ET for East Track. Contrary to all this, the Nickel Plate simply used numbered track circuits like 1T, 2T, 3T (2T being the middle or island track circuit).

So as those of us early adopters of the ATCS Monitor hobby transitioned from Left-Right naming to North-South or East-West, it became a holdover to think of approach blocks to an interlocking or control point as tied to the signal name. And since a train has to be, for example, westbound to get a westbound signal, the track in approach to that signal logically became the Westbound Approach Track, or WA. The "W" meant westbound and not just west. Here is a stick example of such a conversion:

                              O-  A:WG/NW
A:EA________________(TK)___________________A:1WA
              A:NW \          O-  A:WG/RW
      A:EG  -O      \______________________A:2WA

This may go against the defacto standard in the program, and even against modern signal practices. In the history of railway signaling there was great diversity in nomenclature and naming practices since there were so many different railroads. We've lost that with all the mega-mergers. Perhaps using the bounded approach naming scheme is showing respect to signal engineers of the past...

-- Main.DougNipper - 06 Mar 2007