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mbsImage1NMRA-MER MEETING 31 MARCH 2001 - FRAZER, PA

MANUAL BLOCK SIGNAL SYSTEMS

THE INFORMATION HEREIN IS EXCERPTED FROM CHAPTER 7- MANAGEMENT OF TRAIN OPERATIONS - FROM "THE PRR IN THE SHENANGO VALLEY"

COPYRIGHT 2001 BY ALAN B. BUCHAN

MANUAL BLOCK SIGNAL TERRITORY

A Manual Block Signal system, the earliest form of block signaling, is nothing more than a series of sections of track, typically between stations (known as blocks) governed by fixed signals located at the entrance to the block (known as block signals), operated manually by the block operator, based on information received from the dispatcher by telegraph, telephone or radio.

 

The signals at the entrance to each end of the block are not interconnected, either electrically or mechanically, and no track circuits are used. Therefore, the presence of trains in the block has no effect on the aspect of the signals.

Manual block systems may be operated as either absolute block or permissive block. With an absolute block system only one train may be in a particular block at any time, while with a permissive block system, trains, other than passenger trains, may be permitted to follow trains other than passenger trains into the block. Under absolute block rules all trains are protected by a definite space interval and full advantage is taken of the space-interval safety feature.

The permissive system may be used to expedite traffic. However, following trains must obey strict speed requirements, looking out for trains ahead.

The PRR Book of Rules(a.k.a. Rules for Conducting Transportation), effective October 25, 1956 and in effect through the PC merger, contained 29 rules in the Manual Block Signal section (the 300 series of rules) and four rules in the Fixed Signals section that applied specifically to manual block operations. The four-fixed signal rules, illustrated below, were:

Other aspects; including Stop-signal, Restricting, Approach, Caution and Train-order were used in manual block territory but did not convey block authority. The PC Rules for Conducting Transportation pertaining to manual block operations were essentially the same as during the PRR era.

BLOCK STATIONS AND BLOCK-LIMIT STATIONS

The signals at the entrance to a block are controlled from what is known as a Block Station, which in the early days were all manned by Signalmen, later called Block Operators initially using telegraph to communicate with the dispatcher and other block operators. In the early 1900s the PRR introduced the use of unattended block stations and later in 1941 block-limit stations as replacements for the manned block station. The events that precipitated the change to unattended block stations are the result of the perfection of the telephone and the need to reduce operating expenses. When the invention of the telephone (1876) became perfected and reliable enough for railroad train order use, ca. 1904, the need to have a person with telegraphy skills at every block station wasn't necessary. The PRR also found it necessary to reduce its operating expenses because of the impact of the implementation of the "full-crew" law in 1913 and the Adamson Act in 1916 that introduced the 8-hour/100-mile day with time and a half for certain kinds of overtime for the operating brotherhoods. At this time the railroad also found it necessary to make large capital expenditures to restore the physical plant and equipment, which had become deteriorated during the massive movement of trains during World War I. Also after the war, when the railroads were returned to private operation the PRR had a deficit in Net Railway Operating Income cause by a severe winter early in 1920, a switchmen's strike in April, a 21% wage increase in May and a discrepancy between freight rates and wages.

In an effort to reduce its labor costs the PRR began to close block stations. The method of closing a block station was not to abandon them but rather keep them as block entrances and place them under the jurisdiction of an adjacent block station and operator. These closed block stations became known as unattended block stations and were closed on either a part-time or continuous basis. A special "sign" indicating the limit of the block was required to be placed adjacent to the track at an unattended block station.

With the introduction of the PRR's new Book of Rules on September 28, 1941 the Block-Limit Station came into being and the "sign" previously used at unattended block stations became the Block-Limit signal (Rule 293). At that time many of the continuously closed unattended block stations became block-limit stations.

USING BLOCK SIGNALS

Trains were usually authorized to pass block stations on signal indication, in other words by the operator displaying an aspect other than Stop-Signal (Rule 292). In most cases that would be Clear-Block (Rule 280). However, when the block ahead was occupied by a freight train a following freight train could receive a Permissive-Block (Rule 289) aspect provided such operations were permitted in the territory. Passenger trains could only operate in a clear block.

Of course if the train were diverting to a non-signaled and/or non-circuited track such as going into the siding or a yard, a Restricting signal (Rule 290) would be displayed. If for some reason the block signal could not be cleared at a block station, authority to enter the block was given to the train by the block operator issuing a Form C - Clearance Card when authorized by the Superintendent-Transportation.

At block-limit stations there are no block operators and the fixed signal (Rule 293) is such that it cannot be changed. Therefore, block authority is given to the train using a Form K - Clearance Card. The Form K simply authorizes the train to proceed by the block-limit station as though the named block signal (Clear or Permissive) was displayed. This form would have been given to the train prior to its departing the previous open block station or via trainphone, telephone or radio to the conductor and engineman prior to or when the train arrived at the block-limit station.

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Sample PRR Form K - Clearance Card. Actual form is 
5-1/4" x 4-1/2" printed on green paper.

RULE 280
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NAME
Permissive-block

INDICATION
See below
 
RULE 287
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NAME
Clear-block

INDICATION
See below
PRR semaphore fixed signals used to convey block authority in MBS territory. From the PRR Operating Department Rules For Conducting Transportation, April 26, 1925. At this time the block-limit signal had not been established as a rule but was in use, designated as a "sign" in the timetable special instructions to be used at unattended block stations. Position light signals were also in use at this time.
RULE 280
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NAME
Clear-block

INDICATION
Proceed; for passenger trains, manual block clear, for trains other than passenger trains, manual block clear outside yard Limits.
 
RULE 289
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NAME
Permissive-block

INDICATION
Block occupied; for passenger trains, stop; for trains other than passenger trains, proceed prepared to stop short of a train or obstruction, but not exceeding 15 miles per hour.
RULE 293
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NAME
Block-Limit

INDICATION
Limit of the block. (Yellow light next to track governed)

 

RULE 293A
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NAME
Approach Block-Limit

INDICATION
Proceed prepared to stop at next Block-limit signal. Train exceeding Medium speed must at once reduce to that speed. NOTE - Will not apply to trains authorized to pass the Block-limit as though Clear-block signal were displayed.
PRR position light fixed signals used to convey block authority in MBS territory. From the PRR Rules for Conducting Transportation, October 28, 1956. Note - between 1925 and 1956 Clear-block changed from Rule 287 to 280 and Permissive-block changed from Rule 280 to 289. For those interested in replicating these aspects using Penn Central color light signals - Permissive-block was yellow with an "MB" plate on the mast while Clear-block was green with an "MB" plate on the mast with or without rounded end semaphore blades. ABB 03/01