While "section" indeed does refer only to sections of trains in the rule book,
the meaning in Don's dissertation quite obviously was that of a geographical
piece of line. Section is also a term that is used by the accounting
department to describe a section of line for various valuation reasons.
On a single track railway, the line between the absolute signals of
consecutive passing sidings usually has one or two permissive signals. They
increase the line capacity by allowing trains in the same direction to follow
more closely. Additionally, if some track or signal fault (like a burnt-out
bulb) occurs, the requirement to proceed at no more than 15mph is limited to
only a two or three miles, instead of the entire 7-10 miles. When we are
talking about "blocks", I am not sure if the term only applies to the distance
between signals. If so, we have a curious situation where the blocks are not
always fixed, but can be dependent on direction where the intermediate signals
are not opposite each other. This was not uncommon in territory with lots of
curves, to provide decent sight lines. When considering opposing trains, it is
highly desirable to consider the entire single track portion as one "block".
That is built into the ABS signal system circuitry, at least in more modern
times.
The UCOR definition is "A length of track of defined limits, the use of which
by trains or engines is governed by block signals, cab signals, or both". I
think the "defined limits" may vary depending on whether you are considering
opposing trains or following trains. But I will defer to Vic's more intimate
knowledge here.
But all this fine detail is perhaps confusing. Don succeeded in providing a
reasonably close description for common man.
John
---In cpsig@xxxxxxxxxxxxxxx, <thomasd@...> wrote:
As I said, I’m neither a rules nor a signal instructor nor could I become one
without much study. I tried to explain the different types of fixed wayside
signal with reference to different physical circumstances and the different
subsets of operating rules which embody them, in terms which I hoped would be
enlightening to someone who (presumably) does not have a sophisticated
knowledge of the either rules or signals. Some terminological inexactitude is
necessary, and I think excusable, since the questioner probably won’t be taking
any rules classes in the near future. I chose my words carefully to make my
explanation clear and internally consistent, rather than in strict accordance
with the definitions found in the various rulebooks and signal treatises in my
basement. If I were writing a treatise for people with an operating background
I would have chosen my words quite differently and in consultation with rules
and signals people.
Don
From: cpsig@xxxxxxxxxxxxxxx [mailto:cpsig@xxxxxxxxxxxxxxx] On Behalf Of Vic
Sent: November-27-13 8:37 PM
To: cpsig@xxxxxxxxxxxxxxx
Subject: [cpsig] Re: What side of mast for signal target
Posted by: "Don Thomas" thomasd@... mailto:thomasd@... donaldmthomas ;
Date: Tue Nov 26, 2013 10:53 pm ((PST)) Very generally, and not pretending
to be running a Rules or signal design class here: Interlocking signals are
used to protect places where tracks meet or cross. They can be set specifically
for each movement by an operator either locally or remotely, or they can be
triggered to operate automatically to clear a route for each train approaching,
blocking any other train arriving on a different track until the first has
passed. The control mechanisms for the signals and switches are interlocked
mechanically, electrically or electronically in such a way that a signal cannot
be cleared unless there is a safe route through the interlocking zone. This
means all switches (if any) must be set for the train to move through on the
intended route, and there are no other routes cleared which would conflict with
it. Once a signal has been cleared, the switches on the route, and all signals
governing potentially conflicting routes, are locked in place until the train
has gone through (or t he sign al has been set to STOP and a timer runs out).
Not all interlockings have switches, as they can also be used to govern diamond
crossings. But they must all contain signals. An interlocking can involve a
simple diamond crossing or a junction of two tracks, or it can be a complex
beast with a spaghetti bowl of crossovers. Under Interlocking Rules, a STOP
signal is absolute and trains must not proceed after stopping without explicit
permission. The default state of an interlocking signal is STOP unless cleared
to a less restrictive indication. Block signals exist to protect trains
that are not going through junctions. In their simplest form they protect
trains from running into the rear of a train ahead of them. Automatic block
signals are activated electrically by the presence of a train, altering an
electric circuit flowing through the rails. (There are manual block signal
systems, and other manual block systems, which are not relevant to your
question.) Under ABS STOP AND PROCEED is normally the most restrictive signals,
normally meaning proceed no more than 15 mph and prepared to stop short of
obstruction, opposing train, broken rail etc. (Remember this is not a rules
class.) However ABS also allows absolute STOP signals. A simple ABS system is
unidirectional and is used on a double track railway, with the current of
traffic in opposite directions on the two tracks. Absolute Permissive Block
(APB) signals allow ABS to function in both directions on a single track
without head-on collisions or serious delays. AP B provi des absolute signals
at the end of sidings or double track. These are set to STOP when an opposing
train enters the other end of the section, forcing a train to wait there until
the opposing train has gone past. Along the single track the signals are
permissive, i.e. STOP AND PROCEED allowing trains in the same directions to
follow each other. These intermediate signals work the same way as simple ABS
signals. The default state of an automatic block signal is CLEAR unless a train
in a nearby block sets it to a more restrictive indication. Interlocking
signals are wired to work like block signals so the presence of a train will
override a less restrictive indication the signal would otherwise be set to.
Block signals do not convey authority to operate a train. They are overlaid
on the system of written authority used on the railway. Centralized
Traffic Control (CTC) combines some features of interlocking and block signals.
Controlled points such as junctions, siding ends, end of double track, or
crossovers between two or more tracks, are controlled by a dispatcher or rail
traffic controller. These technically are interlockings. The signals on the
main track or tracks between these points are technically automatic block
signals. They are controlled solely by the presence of a train rather than by
the operator. (The controlled signals are also overridden by the presence of a
train on adjoining blocks.) The indications in CTC are consistent with those in
ABS and interlocking rules. The big difference is the rules governing CTC. CTC
signals themselves constitute the authority for train movement within CTC
territory. For the most part, CTC signals at junctions will look and
behave like interlocking signals, and CTC signals between controlled points
will look and behave like block signals. Block signals in ABS generally
have one or two heads. In ABS a two head signal will normally have the heads
staggered to indicate they are permissive. However if there were a two head
signal at a siding end under APB, the heads would need to be vertical to
indicate it is an absolute signal. Interlocking signals may have one, two or
three heads. Signals protecting diverging routes would normally have at least
two. A single head interlocking signal would need an “A” sign to show it is
absolute, and a two head signal would have to be vertical rather than staggered
to show it is absolute. A three head signal can only be absolute; it cannot
give a permissive STOP AND PROCEED indication. Dwarf signals can have only one
or two heads even within interlocking limits. As far as what side of the
mast the signals are placed, I would suggest you research prototype practice
for the locations you are interested in. The only restriction is that a two
head permissive signal must be staggered, and as far as I know the higher head
must be to the left and the lower head to the right. As I warned at the
outset, this is neither a rules class nor a signals symposium. People with
rules cards and signal specialists can correct me ten ways from Sunday. I am
just offering the quick and dirty layman’s 25 cent tour of the subject to give
you a quick grounding. There are lots of better sources on line which can give
you more insight.
Don gave us a superb general outline above. There are a couple of points I
ought to clarify though:
Section: Don used this term in his introduction to APB, itself a concept no
longer recognized under the 1962 UCOR, where APB was simply bundled and
included under ABS as another variety thereof. But the term SECTION in the
context used by Don here is so much at odds with its definition, that "a group
of [consecutive] blocks" would be better wordage in explaining the APB concept
to a operating rules neophyte, w/o destroying the fundamental of Definitions
being keys to understanding rules and concepts. In rules, the definition of
Section limits the terms' application to two or more trains running on the same
schedule and displaying signals or for which signals are displayed. The
"signals" referred to in the preceding sentence are not Fixed Signals [as
defined] but are Classification signals under 1962 UCOR (and all other codes of
rules and most independent operating rules) Rule (hereinafter "§") 20. And
FWIW, APB systems where installed and functional, were only [used] in single
track territories.
Don also said "Block signals do not convey authority to operate a train. They
are overlaid on the system of written authority used on the railway." This is
true and correct in single track territories outside of CTC (§§ 261-273), and
outside of yard (§ 93) and station limits (§ 93a*), but not necessarily so in
Two or More Track territories if §§ 251-257 are in effect, nor any number of
main tracks under CTC, ibid.
* After yard limits were invented, they replaced station limits on most
roads. Notable exceptions were NAR CPR and all CPR affiliates (E&N TH&B DAR QC
etc) where station limits remained in cont'd use but supplementary to, rather
than instead of, yard limits.
All of my rules references abv are to the 1962 UCOR unless otherwise specified.
VRP
London Canada
ex Rules Instructor, Examiner
and Consultant inter alia, ret.
