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Monday, September 2, 2013


How does one operate a commuter rail service on a busy freight main line without resorting to exclusive use windows that drive freight railroads absolutely bonkers? The answer seems to be interlockings, and lots of them! When industry laggard CSX was trying to claw itself out of the dismal days of railroading in the 70's and early 80's it found itself saddled with a pair of passenger routes operating out of Washington, DC on former B&O trackage. With plans for the state operating entity to expand service and buy new equipment CSX correctly realized that it might be bad karma to oppose an expansion of passenger rail service into the nation's capitol and instead worked to turn lemons into lemonade by getting the state to fund a new signaling system on each line.

Sometime between 1990 and 1992 both the Capitol Subdivision and Metropolitan Subdivision were upgraded for bi-directional CTC operation. Both projects were some of the last wherein CSX installed brand new B&O style Color Position Lights, but the Capitol Sub project was also interesting for the sheer number of crossovers installed. Where most railroad CTC mainlines tend to have crossovers about every 8-10 miles, the 38-mile Capitol Sub has one about every 4 miles. Unlike the Metropolitan Sub, the Camden needed to run a bi-directional service during the peak periods to serve both Washington and Baltimore. Service on the Brunswick Line continues to be peak direction only and could get away with a more traditional 8-10 mile crossover spacing.

In 2009 I went out to a pair of these interlockings adjacent to the Dorsey and Jessup, MD stations to document the signals involved and then I returned in 2011 when stimulus money resulted in the early retirement of the 1990 vintage CPL. The complete 2009 can be viewed here, and the 2011 set here.  While neither location retains their CPL's, the historical record of them serves as a nice guide to B&O CPL signaling in a modern bi-directional CTC environment.

Because Dorsey and Jessup interlockings are back to back with no intermediate signals, the westbound masts at Dorsey have 4 orbitals. 12 o'clock for normal speed route, 6 o'clock for medium speed route, 10 o'clock for Approach Medium speed route and 8 o'clock for medium route approaching medium speed route.  Here is the CPL mast for track 1.

And the CPL mast for track 2 displaying a CLEAR indication for a southbound MARC commuter train

 The eastbound signals are simpler only requiring a 12 and 6 o'clock orbital for the medium speed crossovers.

Here in this 2011 view the northbound track #2 signal is displaying Clear for an approaching CSX freight train while Darth Vaders hover menacingly in the background.

All of the signals are of the latest design revision before GRS stopped production. This is identified by the small, corrosion resistant terminator box on the back of the central target. Lamp cups remain unchanged from previous CPL designs.

 Points are powered by a  GRS Model 5F point machine. I also noted that there was no anti-snow devices applied to any of the points at Dorset interlocking. 

The interlocking equipment was located is a somewhat washout susceptible relay hut. The antenna indicates either the presence of the wireless "code line" system called ATCS to eliminate the need for a physical pole line.

Dorsey interlocking was installed new with the early 90's line rebuild and did not replace/enhance an existing interlocking. The interlocking two miles to the west at Jessup existed prior to the line upgrade as it controlled the east end of the yard lead to the Jessup auto terminal and other local industrial tracks. Jessup interlocking is also located adjacent to a station, although the Jessup station sees a smaller number of stopping trains. This allows most commuter trains on the line to use this pair of interlockings to leapfrog any freight trains traveling the route.

As the interlocking was rebuilt and not new, it retains a B&O style bracket mast at each end.

Unlike the signals at Dorsey, the westbound signals at Jessup have a central target with a complete circle of lights. This allows for the signals to display a Restricting (lunar \) aspect instead of just Stop and Proceed (Red -- with a 6 or 12 o'clock orbital lit). For westbound trains this was useful for train entering the non-signaled yard lead. Today with Restricted Proceed replacing Stop and Proceed there is in theory even less use for the dedicated restricting aspect. The presence of 8 and 10 o'clock orbitals is also a bit puzzling as while the next signal is an interlocking, it does not provide for a diverging route on either track. It could be due to the fact that the second signal block between the next interlocking (PA TOWER) and the interlockinf after that (SAVAGE) is slightly shorter at 1.5 miles and 4-block protection is therefore needed.

The eastbound signals feature the 8 and 10 o'clock orbitals due to the presence of Dorsey interlocking, but also support the Restricting aspect even tho there are no routes leading to non-signaled track. This could be an artifact of earlier B&O signals at this location having that indication.

All 4 signals use the newer GRS revision termination box, but they seem to be a bit older than the ones at Dorsey. Jessup may have been rebuilt first to support to auto terminal and then revised to support bi-directional operation.

 All the turnouts at Jessup are fitted with electrically powered ducted snowmelters, which contrasts strongly with the turnouts at Dorsey which have no snow melting facilities whatsoever. The reason is due to what is called a "snow plan" allowing for cost savings in snow removal gear. During a snow plan certain switches are restricted from use in order to prevent a points failure that might delay trains and require a maintainer to fix. Because the crossover at Dorsey is 1.7 miles from the crossover at Jessup, in a snowstorm there is no reason to need both sets of crossovers and therefore Jessup is included in the snow plan and Dorsey let out.  Just because one can assume that having two interlockings so close would make one redundant doesn't mean that MARC can't run its regular level of service in a snowstorm.  The local commuter service has its own plans for reducing service in inclement weather as well.

The relay hut is of the same design, but the point machines are standard GRS model 5H's instead of the compact 5Fs seen at Dorsey. Also note the point heater ducting.

Finally, the signal coming off the yard lead is fitted with a B&O CPL dwarf with a 6 o'clock orbital for medium speed moves. I am not sure what trains also diverging at Dorsey would get as the 8 o'clock orbital is absent. I am guessing they would either get a Medium Approach or a Slow Approach Slow (Green | w/ no orbital lit).  Medium Approach would also satisfy the safety conditions for a diverging movement at Dorsey.

The 2011 re-signaling cast doubt on the whole Medium speed switch idea hinted at by the dwarf CPL as the signal governing movements off the lead offered slow speed routes only.  Either the re-signaling downgraded the switch or the dwarf was a retread that had the 6 o'clock orbital left in place. In that case Slow Approach Slow would have been the most likely indication for a diverging move at Dorsey.  With the re-signaling thanks to CSX not having a color light indication for Slow Approach Anything, a R/R/Y Slow Approach would be needed.  The only other Slow Approach Medium indication I could find was in Canada (of course!) which uses R/*Y*/G.

Also note the 2011 re-signaling was adding a power operated derail to the extended yard lead. Probably a wise precaution.

That's all for this edition of Know your B&O CPLs.  Some time in the future look for other brief posts on other formerly or currently CPL lit interlockings on CSX main lines and how the most theoretically advanced signal aspect system in North America worked in practice.


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