Many railroads installed Centralized Traffic Control to increase traffic capacity on a line operated by the traditional Time Table and Train Order (TT&TO) system. A CTC-line typically has automatic block signals every few miles and power operated switches at all sidings/crossovers, continuously enabling the dispatcher to swiftly and efficiently optimize traffic. Since CTC was and is expensive creative minds worked on approaches to reduce installation and maintenance costs. The results of this are often referred to as "Poor Man's CTC".
"Poor Man's CTC" took many different forms and shapes on the different railroads. Reducing costs meant reducing functionality and the solution chosen by a given railroad would usually depend on the railroad's primary objectives for CTC-installation and perhaps some re-use of existing ABS-equipment. Some ways of cutting costs were:
CTC on the P&WV was a combination of the above approaches plus some more. Or less, more correctly, as the P&WV went for an even simpler but quite clever kind of CTC. This type of CTC is more officially referred to as "Modified CTC". The description below shows the application on the P&WV RR based on information from signal charts, photos and information from people who knew the line. In particular I'd like to thank E. Roy Ward and Gene P. Schaeffer for their help. Additional information and corrections are much welcome.
The Poor Man's CTC on the Pittsburgh & West Virginia Railroad (P&WV) was installed around 1950 by Union Switch & Signal on the mainline from Connellsville PA to Pittsburgh Junction OH. The P&WV was part of the Alphabet Route and was at the time a semi busy mainline. After having been part of the Norfolk and Western since 1964 the line in 1990 became the eastern leg of Ohio based regional Wheeling & Lake Erie Railroad. The CTC was decommissioned around 1992 but many of the signals still stood almost 10 years later. The eastern part of the line saw very little use around the turn of the Millenium but in later years traffic has picked up again.
A typical siding on the P&WV would look as shown below. For the P&WV signal aspects and indications please refer to "Signal Aspects and Indications, Pittsburgh & West Virginia, 1953".
The siding is "unbonded" i.e. has no track circuit and the siding switches are both spring switches. The western end of the siding forms a standard CTC "Control Point", though the spring switch places it the "Poor Man's" category. The controlled signals are preceded by approach signals on the line but these do not serve as intermediate block signals. Thus a block reaches all the way from one siding to the next.
The eastern end of the siding is a bit more unusual. Here the CTC did away with the main track signals and only kept a dwarf signal in the siding to authorize eastbounds back out on the main (signal 10Ls). A westbound train on the main would therefore have authority to proceed all the way to the western Control Point (CP), signal 12R. With this setup meets have to be executed by the eastbound train taking the siding and the westbound staying on the main.
At the point of the eastern switch is a spring switch indicator, indicating by red or green whether the switch is properly lined for the main track. The indicator is just that and is not controlled by the CTC. The CTC signals are, however, supervising the switch as well. Signal 151 is located as an approach signal to the eastern switch even though it's really the approach signal to signal 12R. My interpretation is that this is to provide sufficient braking distance in case the switch has been opened. The controlled signal at the previous siding would also stay red if the switch was open but this may be quite far away and allow too large a window for error.
Some sidings were equipped differently. Some had a power switch at the west end but otherwise the same arrangent. This would allow the eastbound train to head directly into the siding, though the unbonded siding still keeps the train at Restricted Speed. Other sidings had controlled signals at both siding switches and were a more traditional "Poor Man's CTC", thus allowing meets to be executed both ways.
In order to illustrate the P&WV CTC let's see how trains would move across the line and meet. The examples below show a section of the line with two sidings, Lefton and Righting. Lefton is equipped as the example above whereas the Righting has a power switch at the west end. To begin with the line is sitting idle:
The line was last used by a westbound train. This can be seen by the intermediate signals 151 and 269 showing "Approach" whereas signals 178 and 294 show "Stop and Proceed", indicating that the CTC is set for westbound movements though no controlled signals have been cleared.
First, an eastbound train, EB1, is to take siding at Lefton. The train is lined through the west Control Point at Righting and signal 16L (and its approach signal 294) is displaying "Clear". This authorizes the train to proceed to Lefton signal 12L. Lefton's west switch is a spring switch that the train crew will have to throw manually. Signal 12L indicates this by red lights over an illuminated "S", meaning "Take Siding". Approach signal 178 shows "Approach". Note that signal 151 shows "Approach" since the line section here is still lined west:
As EB1 moves east it releases blocks and routes past Righting, until the train comes to a stop at Lefton signal 12L:
When the crew has lined the spring switch reverse the train has authority to proceed into the siding:
After the train has entered Lefton siding the train crew sets the spring switch back to normal. The CTC was designed in the times of cabooses and had the system still been in operation today the switch might have been left in reverse until a meeting westbound came to a stop at 12R to line it back:
With train EB1 now in Lefton siding the dispatcher lines another eastbound, EB3, into Righting siding. The switch here is a power switch so the dispatcher can reverse it himself and signal 16L shows "Restricting". The dispatcher also lines a westbound train, WB6, past Lefton signal 12R to 16R at Righting:
After EB3's arrival in Righting siding the dispatcher lines the power switch back and clears WB6 further west. At the same time WB6 passes over the east spring switch at Lefton. Note how the spring switch indicator's green has nothing to do with track occupancy and stays green. It only indicates that the spring switch is in normal position:
As WB6 clears the interlocking at West Lefton the block becomes free after it. This allows the dispatcher to clear the dwarf signal 10Ls, authorizing EB1 back onto the mainline going east:
As EB1 trails the spring switch the switch indicator goes red since the switch is now open:
With train WB6 now past West Righting, EB3 is lined east. Note that since EB1 is still in the block EB3 can not be authorized further east than Lefton signal 12L:
When EB1 clears the block EB3 can be lined through 12L as well:
This concludes the major principles in the P&WV version of "Poor Man's CTC". The P&WV CTC also included junctions with branch lines that were quite standard CTC. There were cases of sidings close enough that the approach signals on the line were omitted. Instead the controlled signals included an "Approach" aspect in these cases:
Text, Images, HTML: Carsten S. Lundsten.