Nostalgia & History > Approach Medium or Advance Approach

Most times when a signaling question comes up on TO the discussion gets bogged
down over regional differences and applications.

Risking that, here is a post that I hope you find educational.

The Approach Medium was mostly used by the eastern railroads that had speed signaling.

From a time when thought was put into projects with the idea of saving time and money
in the operation of trains. 

From the April, 1948 issue of Railway Signaling, digitized by the good people at Google Books.

---

Very interesting post. Some years ago, I got to know a professional in the signalling field, the late Robert McKnight, who donated his papers on railroad signalling practice to the Barriger Railroad Library. I had a number of conversations with him on such issues regarding what might be called the theory or philosophy of signalling. At the time, I did not have an appreciation of such issues, and sometimes I could barely keep up with his points. As a non-railroader, I just did not have an appreciation or experiential understanding of the issues involved. I also number as a close friend of many years a railroad manager who has deep experience in operating practices, rules development and promulgation, and operational training and rules / safety practice. Conversations with him on such matters were also very interesting, and perhaps because he had much closer and more regular contact to operating crews than did an engineer like Mr. McKnight, the conversations tended to be somewhat more comprehensible to this non-railroader when we got into the finer points.

In recent years, I have been active in running various railroad simulation programs, including the original Microsoft Train Simulator, its successor OpenRails, and Run 8. I won't vouch for the accuracy of the signal systems in these simulators in properly displaying proper aspects relative to train positions in the sim at the time. They seem to do a pretty good job to this layman's viewpoint. But that's not really the point. The real point is that it finally gave me an appreciation and understanding, however incomplete, of the kinds of issues raised in this article, and that I used to sometimes discuss with Mr. McKnight and my friend. As a railfan photographer standing trackside, maybe with a view of just one or several signals in sight, it just wasn't possible to really understand all of the issues involved, even if one knew how to read the signal aspects that were visible and to understand them. In the train simulators, again whether accurate or not in their display of aspects, I gained a whole new appreciation and level of understanding about these issues because I had to properly respond to them in handling the train I was running in the simulation at the time. And thus I gained a much greater appreciation of their importance.

It will be very interesting to me to read the comments of professional railroaders on this thread. Hopefully the discussion will be able to not get too bogged down, as Englewood said, in the technicalities of regional differences. I'll step back now and let the professionals comment. Thanks, Englewood, for this thought-provoking post.

MC
Muskegon, Michigan



Edited 2 time(s). Last edit at 04/08/20 10:02 by ironmtn.

> Approach Medium was mostly used by the eastern
> railroads that had speed signaling.

AFAIK, if you don't have speed signals you can't have Approach Medium -- just Appr Diverging and/or Adv Appr.

timz Wrote:
-------------------------------------------------------
> > Approach Medium was mostly used by the eastern
> > railroads that had speed signaling.
>
> AFAIK, if you don't have speed signals you can't
> have Approach Medium -- just Appr Diverging and/or
> Adv Appr.

Approach Medium has been used in conjunction with route signaling for decades. Often, Medium Speed was not defined in the rules, but the speed limit was shown in the indication rule.

TAW

Englewood Wrote:
-------------------------------------------------------
> Most times when a signaling question comes up on
> TO the discussion gets bogged
> down over regional differences and applications.
>
> Risking that, here is a post that I hope you find
> educational.

That argument went on for a long time, basically until relatively recently.

There is an additional argument that was not a common situation in 1948. With heavyweight passenger cars, 4,000 foot freight trains and steam engines / early diesels, stopping distances among trains was somewhat uniform. In recent times, there is a wide variation in stopping distance. Depending upon the train, passenger stopping distance from 80 mph can be half that of a freight train at 60 mph. Spacing signals for passenger stopping distance but giving a 4th indication for freight trains or putting signals at freight stopping distance and giving passenger engineers the opportunity to reduce speed at a point appropriate for their stopping distance would maximize capacity. However, it depends upon  the engineer's judgment to control the train at a point that is not specifically at a signal.

I tried promoting the use of Advance Approach when I was developing the Sounder and Cascades services. Some of the discussion I was involved in turned into a couple of papers by university engineering students years ago. The point was an attempt to improve mixed traffic railroad capacity and utilization. Not only did it not gain any traction, I hit a virtual brick wall at BN when the signal department told me that three-indication signals increased line capacity over 4-indication signals. (hint - that is WRONG)

It is a Really Dead Issue now because PTC needs a specific speed for every signal indication. Engineer judgment is trusted even less now than it was a couple of decades ago.

TAW

TAW Wrote:
--------------
>
> Approach Medium has been used in conjunction with
> route signaling for decades. Often, Medium Speed
> was not defined in the rules, but the speed limit
> was shown in the indication rule.

What route-signalled RR used Approach Medium?
Was it yellow over green?

timz Wrote:
-------------------------------------------------------
> TAW Wrote:
> --------------
> >
> > Approach Medium has been used in conjunction
> with
> > route signaling for decades. Often, Medium
> Speed
> > was not defined in the rules, but the speed
> limit
> > was shown in the indication rule.
>
> What route-signalled RR used Approach Medium?
> Was it yellow over green?

Off the top of my head, BN and Santa Fe - Flashing Yellow.

TAW

Yup, I was wrong -- the 1975 SFe book calls flashing yellow Approach-Medium and the indication is what you'd expect.

Approach Medium was also found on ex-Milw trackage of the CP.
Flashing Yellow. Proceed. Pass next signal not exceeding 40 mph.

The Rock Island also used it.  The 1950 book shows Yellow over Yellow or a Flashing Yellow.
30 mph at the next signal.

The BN got in trouble with the FRA over the use of the Approach Medium on the East End.
As I recall it was about 30 years ago.  On the East End the Approach Medium (Flashing Yellow)
was used as both an Advance Approach and Approach Diverging.  I believe it called for 35 mph
at the next signal.  That was fine when the crossovers were good for 35mph but the Engineering
Dept. at some point changed the speed through the turnouts to 30 mph. The FRA took exception
to that and the BN had to put in Approach Diverging aspects.
 



Edited 1 time(s). Last edit at 04/08/20 17:26 by Englewood.

TAW Wrote:
-------------------------------------------------------
 Not only did it not gain any
> traction, I hit a virtual brick wall at BN when
> the signal department told me that
> three-indication signals increased line capacity
> over 4-indication signals. (hint - that is WRONG)
>
Too bad the BN threw all their old issues of Railway Signaling in the trash.
The young guys might have learned a thing or two by paging through them.

Englewood Wrote:
-------------------------------------------------------

> Too bad the BN threw all their old issues of
> Railway Signaling in the trash.
> The young guys might have learned a thing or two
> by paging through them.

Nah. It is so much more satisfying to make stuff up and claim superiority of knowledge.

TAW

Bingo.

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