Here is some poop on Santa Fe Railroad's Rule 251.
FYI: Text is pasted from a document I wrote previously. Graphic images were made by me using AutoCAD R14, then turned into Gifs with Paintshop Pro.
(I hope this post is interresting to everyone!)
ATSF Railroad's "Rule 251" Descriptions.
This describes the functions of Rule 251, which was in effect from 1920 until June 4th, 2001.
This was when the last portion of Main Line Trackage was changed over to CTC (Centralized Traffic Control).
The functions of Rule 251 are unique to ATSF, due to several reasons:
1: Traffic Control in a "Two-Track With Outside Sidings" area,
2: Signal Aspects on "Automatic Signals" which are "Absolute" (explained later),
3: Non-Automatic control of Turnouts,
4: Conductor of Train determined when to "Go Into The Hole",
5: Avoid delays to not just the "Priority" Traffic, but to all Traffic,
6: ATSF Used the "Left-Hand" Rule.
**BASIC AND BRIEF DESCRIPTIONS***
*Two-Track Mainlines with Outside Sidings:
Traffic moved on Two separate Main Tracks - Westward Traffic moved on the "South Track"
(with your Left arm facing West, the Track closest to you is the "South" Track),
and Eastward Traffic moved on the "North Track".
At certain intervals, each Mainline has a Passing Siding - termed "Outside Sidings".
When a Train takes a Siding, it "Goes Into The Hole"
Signals which work Automatically to describe the state of Traffic between Block Points.
These Signals may be "Passed While Red" with restrictions (Stop then Proceed at restricted speed, etc.)
Automatic Signals are not controlled by Dispatcher(s), instead they are controlled by the Absolute Block Signals and Traffic.
Signals which are Dispatcher Controlled. Absolute Signals may not be passed while Red (unless allowed to by Radio Contact to Dispatcher).
These Signals are found at Sidings, Crossovers, and other crucial points.
An additional Track of limited length (typically 6,000 to 9,000 feet), which connects to the Main Track via "turnouts" (Switch Tracks),
for the purpose of allowing one or more Trains to pass.
In most applications, the Turnouts at each end of the Siding are Automatically controlled by the Dispatcher, via Motorized Switch controls.
On Two-Track / Rule 251 Territory, the "Head-In" switch (Turnout which the Train enters the Siding) is Manually Thrown to allow the Train
to take the siding (done by that Train's crew), then relined to normal position once the Train's last car clears the switch.
The "Head-Out" switch (Turnout at the "Exit" side of the Siding), is a "Spring Switch" - a Turnout which operates via a spring,
so a Train may simply move through it without the need of Manually throwing it.
In 2-Track CTC Territory, there are no Outside Sidings - only "High Speed Crossovers" which are used to cross traffic from one Track to another
at speeds above the restricted 10 - 25 MPH of a Siding. CTC Crossovers are typically listed for 50 MPH.
According to the direction which the Traffic is flowing, the Signals or Sidings will be on the Left Hand side of the Train.
This was an "odd idea" in the days of Steam Locomotives - especially when the days of Locomotives with Large Boilers, like 4-8-4 Northerns,-
which made visibility of Signals to the Engineer difficult.
To address this problem, ATSF deployed all Absolute Block Signals on Towers, instead of on Masts.
2 flavors of Signal Towers were widely used by ATSF:
The "Bridge" type and the "Cantilever" type - both made by Illinois Steel, Inc.
ATSF loved the Cantilevers, and used them more than any other North American Railroad.
By 1940, the most common Signal used was the Union Switch & Signal "H-2" Searchlight Signal.
This was a Single Lens type Target Signal, with three colored gels on a rotary disk - Red, Yellow and Green.
Other types of Signals used were US&S 3-position upper quandrant Semiphores (Style "S" and "T-2"),
and US&S "Style L" 3-position color-light (one lens per color).
*Power For Trackside Signals - Three Basic Designs:
1: Primary: Where system power is supplied by Batteries Only-usually a bank of wet cells located at each Signal.
The drawback is the expense of Maintaining the Batteries, the advantage is low first cost.
2: Primary AC: Where system power comes from Commercial power lines.
Lamps, relays and Motors are powered by Line AC, stepped down by Transformers.
The drawbacks are if the AC power goes dead, the Signals do too! Advantage was no Battery maintenance.
3: AC Float: This combines both Batteries and Primary AC together.
Equipment is powered from the Batteries, and the Batteries are charged by the AC step-down Transformer (and Rectifier of course!).
During normal operation, this combination functions similar to an Automotive Charging System.
If the AC power is interrupted, the systems may continue working without interruption (like UPS systems).
This setup requires the most up front cost, and includes nominal Maintenance costs; but this is offset by it's ability to keep traffic safely moving.
(The following items are exerpts from the January 2003 edition of Trains Magazine, edited by me for this article)
***RULE 251-TEXT EXPLAINATION***
In Santa Fe's Rule 251 territory, if one Train wanted to overtake another, it was done on an outside Siding.
Spaced about every 6 miles, they kept the railroad fluid and enabled 100MPH streamliners to co-exist with 40MPH freights.
Almost all had dwarf signals to protect the mainline, and spring switches at the outbout end.
("dwarf" signals are single lens signals which are mounted at Ground level - as opposed to mounting on masts or towers)
On the Santa Fe, all freights operated as "Extras" (they were not listed in the timetables).
To occupy the main in 251 territory, a freight conductor needed only a Clearance Card from the Dispatcher before departure.
The Extra could then run on signal indication (the Automatic and Absolute signals).
However, it was the conductor's responsibility to clear the main track to avoid delaying all "Superior" trains listed in the timetable.
Where specifically to clear was left to the conductor's judgement, an agressive conductor might naturally wait for the last possible siding to clear the main;
but delay to any first class train was not tolerated.
The only other time a conductor would clear the main was by train order issued by the dispatcher and delivered at an open office.
After the advent of Track Warrent Control (TWC), the operation was nearly identical, except the dispatcher issued the orders verbally (Radio).
The outside siding in Santa Fe 251 territory is now extinct, but before their removal (Last to go was signal 2492 on June 5th, 2001) it was possible to monitor movements by observing
a combination of the siding dwarf and main line signal.
Below is an illistration of a Westward movement at a typical outside siding; Adamana.
***RULE 251-VISUAL EXAMPLE***
Below is a series of Graphical Descriptions of Rule 251:
Legend Of Symbols And Color Schemes
-continued on next posted message-