PHOTOS: GREENBELT - The Last CPLs

In the fall of 2014 CSX completed multi-year re-signaling efforts in the heart of its former Baltimore and Ohio territory that included the Philly, Capitol, Metropolitan and Cumberland Subdivisions. B&O style Color Position Lights, some installed as late as the 1990's, were replaced by the typical hooded traffic lights. Beyond the odd siding exit, drawbridge, diamond crossing or distant on non-signaled track, the main line CPL era east of the Ohio River was over. There was however one notable exception on CSX in the form of GREENBELT interlocking in Greenbelt, Maryland. Located just inside the Beltway adjacent to the DC Metrorail-MARC transfer station of the same name, GREENBELT was distinctive in being an interlocking that only really served the MARC commuter train service. These CPL signals would stand for an additional 6 years until their replacement in late 2020. In May of 2020 I went out to GREENBELT for a documentation run so I could present to you photos of The Last CPLs.

GREENBELT interlocking was installed in 1992 as part of a general re-signaling of the Capitol Sub to better support the MARC Camden Line. This saw the elimination of any residual Rule 251 ABS territory, a new Camden terminal complex in Baltimore and the closure of any remaining manned towers such as JD TOWER in Hyattsville. Both the Capitol Sub project and a similar one on the Metropolitan Sub turned out to be some of the last where B&O CPLs were installed new. Like several of the new Capitol Sub interlockings, GREENBELT was commissioned solely for the benefit of MARC commuter trains and consisted of two side pocket tracks that would provide an ADA compliant high level platform connection to DC Metro's new Green Line terminus (The The Americans with Disabilities Act having recently come into force). Pocket tracks were necessary as high level platforms conflict with the clearance envelope of main line North American freight trains. The interlocking consists of two switch pairs, #1 and #2 and 4 signal pairs, 1E/1W. 2E/2W, 3E/3W and 4E/4W.

The signals were in turn broken down into 4 high mast CPLs for the main tracks and 4 dwarf CPLs for the pocket exits. The dwarf signals were placed following the old "right hand" style, while the high masts were not.

In addition to the 12 o'clock orbital for normal routes, eastbound main track signals sported 6 o'clock orbitals for Medium speed diverging movements into the pocket tracks as well as 10 o'clock orbitals for Approach Medium indications for crossover routes at AMMENDALE interlocking, one full signal block beyond GREENBELT.

Eastbound pocket track signals featured a 6 o'clock orbital for diverging routes back onto the main line as well as an 8 o'clock orbital for Medium Approach Medium indications when trains needed to immediately diverge again at AMMENDALE.

 
The westbound signals have a slightly more complicated history. As originally configured westbound main track signals featured both 10 o'clock and 2 o'clock orbitals for Approach Medium and Approach Slow indications respectively. This is because GREENBELT was also one signal block away from the former JD TOWER complex in Hyattsville. Trains approaching from the east would get an Approach Medium for track 1 to 2 crossovers or routes onto the Alexandria Extension at RIVERDALE PARK interlocking. However if a Stop signal was displayed at JD TOWER interlocking, a Slow Approach indication would be displayed (at least for diverging routes) at RIVERDALE PARK due to the short block distance between RIVERDALE PARK and JD TOWER. This then necessitated an Approach Slow capability at GREENBELT.

The westbound dwarf signals operated in a similar manner, just with a full row of lower orbitals including an 8 o'clock orbital for Medium Approach Medium and the somewhat rarer 4 o'clock orbital for Medium Approach Slow.

Unfortunately, the decision to place GREENBELT and RIVERDALE PARK interlockings adjacent to each other created a monster 3.7 mile long signal block that clearly resulted in operational problems as several years before the 2012-2014 re-signaling, a new color light intermediate signal location at Milepost 30.8 was installed between GREENBELT and RIVERDALE PARK. This absorbed the responsibility for the Approach Slow indication from GREENBELT and the 2 and 4 o'clock orbitals were duly deleted from the affected westbound signals.

On the dwarf signals this left a vestigial mounting bracket for the 4 o'clock orbital.

Since nothing can ever be simple, the insertion of the 30.8 intermediate signal converted one overly long signal block into a pair of overly short signal blocks. This meant that the westbound signals would need to retain an Approach Medium or Medium Approach Medium capability for trains needing to get stopped at RIVERDALE PARK and possibly JD TOWER as well. During my 2020 visit, a general lack of late afternoon traffic on the Capitol Sub to/from Baltimore had the dispatcher line up the first pair of MARC locals over two hours in advance! This resulted in the 2W signal displaying the otherwise hard-to-catch Medium Approach Medium indication for an extended period of time.

In a twist of fate, the reconfiguration resulted in #2 pocket track's 4W dwarf's Medium Approach Medium indication going from possibly the interlocking's rarest (since MARC trains using the pocket have few reasons to turn turn onto the Alexandria Extension DC freight bypass route), to one someone could reasonably expect to catch during a reverse running event.

A somewhat non-standard feature of GREENBELT was the failure to employ Medium Approach Medium capability for pocket track movements. Instead trains would enter the pocket on a Medium Clear, just to immediately encounter another Medium Speed signal to exit the interlocking. I guess since the train never leaves GREENBELT interlocking it can be argued that the first Medium Clear's instruction to proceed at Medium Speed through all turnouts applies to both ends of the pocket track. 😅

Moreover, diverging to a stop at the pocket exit signal results in a Slow Approach indication despite the 30.8 intermediate not supporting Approach Slow. It is likely that the pocket track block is so short trains just get an Approach at 30.8 and then diverge over Slow Approach to stop. Both of these quirks can be considered non-standard, yet neither is unsafe.

The re-signaling would generally keep the same plan of signal indications, however the dwarf signals would be replaced by ambidextrously placed color light mast signals. If you are wondering, the three lamp bottom heads on all the main track masts is to support R/R/Y Slow Approach to pocket exit Stop conditions, not a change to a R/Y/*G* Medium Approach Medium pocket track entrance.

While I was doing my thing, CSX signal crews were on site working on the replacement and I was afforded the opportunity to get some photos of the 1992 relay hut on the east end of the plant. This was a track circuit and indication hut, not the central hut with the interlocking logic and local control board, but I'm not going to be picky. Here we can see the general layout with power equipment on the left, signaling equipment on the right and the cable terminal board at the rear.

Despite being a General Railway Signal plant, the vital signal logic consisted of digital cards of Union Switch and Signal manufacture. From right to left the cards appear to be a signal state code transmitter for both eastbound tracks, two indication cards for the 1E/W and 2E/W signals, two vital isolated output cards to control relays related to the 1E/W and 2E/W signals, a CPU card and a power supply card.

Surprisingly the US&S cards were co-located with original 1992 vintage GRS glass case plug type relays. Click here for a full resolution version with legible text. The lead sealed mounting nuts are a nice touch.

While I don't have a definitive answer as to why GREENBELT got a 6 year CPL extension, I strongly believe that it is related to its function to serve the new DC Metrorail station. One likely scenario is that Metro or MTA Maryland may have obligated itself paying for all upkeep related to a new interlocking with absolutely no useful purpose to CSX. Having declined to fund a replacement in 2014, the matter could have been forced by PTC deadlines with replacement being a better "value" than upgrade. Another possibility is that the use of Federal funds for the 1992 project had a minimum life expectancy which only recently expired or Maryland was waiting on additional Federal $ to complete the replacement that CSX refused to fund on its own. Either way I am thankful for the opportunity to have gotten out and taken these photos with my 2020 signal documentation practices instead of my less comprehensive 2014 practices. If you are interested in the full set of photos you can find them here The full set of these photos can be found here ( mirror ).