Thread by @A320Lga

Perhaps one of the more fascinating freight rail operations issues in the Northeast is the unending saga of Allentown and Enola, the two somewhat duplicative and inefficient Eastern PA hump yards that no one has figured out how to consolidate.

These yards, both owned by Norfolk Southern, serve a critical function insofar as they sort most carload traffic moving from the South to the Northeast, and handle most local traffic moving to points on the NS network east of the Susquehanna River.

Before we dive in, some background...

...on hump yards
en.wikipedia.org/wiki/Classific…
...and on Conrail
american-rails.com/conrail.html
Plus a map of PA railroads...
gis.penndot.gov/BPR_PDF_FILES/…
...and a map of the NS system (with a PDF link at bottom for those who prefer)
nscorp.com/content/nscorp…

To fully understand how things got the way they are at Harrisburg and Enola, one must understand the historical geography of the region's railroads, because fundamentally, the story of these two yards is one of infrastructural mix and match and mission creep.

Back in the era before Conrail, Penn Central (and its predecessors PRR and NYC) really was the dominant carrier into the NE. Its routes carried the most tonnage, had the best structure, and -- critical to our story -- had the most and largest yards.

When Conrail absorbed the PC (along with 5 other RRs), it gained control of all that infrastructure, with the oh-so-important exception of the Boston to Washington Northeast Corridor, which moved to Amtrak or had already been sold to commuter operators.

Conrail, not wanting to pay fees to NEC owners for freights on the corridor + recognizing the merit of separating passengers and freight, started shifting traffic away from the NEC. That spelled the end for electric freight trains, and began the yard saga.
flickr.com/photos/5632/13…

When the NEC was a viable freight main, E-W traffic from Pittsburgh and points west traveled into the NE via what's now the Keystone Corridor to Philadelphia (and onwards to NYC via the NEC) or via the Port Road branch, a line from Harrisburg to Baltimore.
multimodalways.org/docs/railroads…

Those traffic patterns gave rise to a massive yard at the natural aggregation point for traffic: Enola, near Harrisburg, where the lines from Philly/NYC and Baltimore converged before crossing the Alleghenies. (Red = PRR, green = Reading RR; keep this in the back of your mind)

(I should note: a decent amount of pre-sorting was done even further west at Conway Yard near Pittsburgh, but that yard had/has its own capacity stress issues and cannot fully aggregate and distribute all E-W Northeastern traffic, and obv can't deal w local industry hence Enola)

N-S traffic moved overwhelmingly through Potomac Yard, a _massive_ facility in Alexandria, VA where traffic from the south was forwarded onto the PRR/Penn Central (and onto the B&O).

Thus evolved a high-functioning freight geography, with big, well designed yards placed at the southern and western entry points to the region. (There also was a big yard on the ex-New York Central main line near Albany, which took some ex-NEC traffic but isn't _super_ relevant)

But then traffic started to move off of the NEC. Between Harrisburg and New York/Philly, the routes of choice were a bricolage of ex-Reading, CNJ and Lehigh Valley lines that carried freight through Reading and Allentown and then into the metropoles.

For traffic that had previously used Potomac Yard, Conrail's solution was to slowly reroute trains going south via an old, somewhat unimportant Reading RR gateway in Hagerstown, MD, or use trackage rights via CSX into Washington.
multimodalways.org/docs/railroads…

This had an impact on yards. Whereas Enola once had been a through yard, w trains to/from Pittsburgh arriving at its north end and those to/from NE cities at its south (red), the increased use of the ex-Reading line east of Harrisburg meant most traffic went around Enola (orange)

...making Enola into a much-less-efficient stub facility.

Likewise, whereas sorting of North-South traffic had previously occurred at Potomac Yard, the new Hagerstown pattern had no yard along it, meaning the cars had to be sorted somewhere else in PA.

The former set of issues -- traffic diversions in the Harrisburg area -- were somewhat ameliorated with the rebuilding of Allentown Yard. While poorly placed for PHL traffic, the yard could serve as a hub for moves to/from Northern NJ and NE PA.

The latter set of problems was essentially dealt with by scattering classification duties across other yards -- in Allentown, Selkirk, Philadelphia, Newark and elsewhere, which worked well enough given Conrail's comprehensive Northeastern coverage.

The upshot: Enola was all but abandoned (Conrail closed the hump there in '93), Allentown got very busy, and freight trains got moved off the NEC

...but that isn't the end of the facility.

In 1999, CSX and NS split Conrail, creating two large east-coast freight networks. NS received all of Conrail's Harrisburg network -- so the Port Road Branch, the new main to NYC/Philly, and the ex-PRR main heading west.

But NS, unlike Conrail, could handle north-south traffic on one network, an advantage on which they capitalized. Problem was, they had nowhere to sort said traffic once it got to the Northeast (which it did via Conrail's old Hagerstown line)

Unlike Conrail, NS didn't have access to tons of yards to spread southern traffic, they really just had Allentown (Oak Island in Northern NJ was still around, but joint CSX-NS ownership and its positioning at an extremity of NS's eastern network made it a poor choice)

Allentown, for its part, was overloaded and inefficient: sorting some NJ/almost all NE PA traffic was a big task, and the yard's layout (hump switching moves frequently interfere with onwards traffic) meant routing more traffic through it would likely just create congestion.

(twitter won't let me add more tweets, but make no mistake: I'm not done yet 🤪)

The result of NS's conundrum: they reopened Enola, and used it through the aughts and early 2010s to handle north-south traffic. Enola is...kinda terrible for this job: trains have to do a full circuit around Harrisburg, and only then enter the yard.

Moreover, because the eastbound receiving yard is so close to where trains come off of the main line, congestion in the yard preeety quickly translates into trains stacking up throughout the Harrisburg terminal area, despite PRR's amazing grade separations

These issues were, of course, an important part of Conrail's calculus to abandon it, and I'd imagine that if it weren't for their presence, Enola would be playing a much larger role in Northeastern NS traffic than it does today (given its growth capacity, if nothing else).

So, for most of the 2000s and 2010s, NS had to work with two yards involved in sorting NE traffic. This meant lots of inefficient duplication of work, lots of transfer runs between the two, needlessly long shipment travel times, etc.

Thanks to the reliance on classification yards, however, there was little they could do about it: you had to sort the cars _somewhere_.

Then, PSR happened. One of PSR's (some background info en.wikipedia.org/wiki/Precision… freightwaves.com/news/what-is-p…) core tenets is that cars should be yarded as few times as possible. This...makes a lot of sense: every time a car has to be classified, it adds 12-30 hours to trip time.

It achieves this by doing a number of things that are, in traditional railroading, a big no-no. It mixes general freight and intermodal traffic, it swaps blocks of cars (groups going to the same place) wherever possible, it tries to make everything daily.

As those articles discuss, PSR isn't a simple positive, but for its failings it is the only operating philosophy that has addressed this (over)reliance on yards and balkanization of networks by commodity. So I'd argue it's a net positive, but that's for another time.

Relevant here is that PSR has closed the Allentown hump yard. With pre-blocking now so ubiquitous, most of Allentown's work that isn't related to local customers has been shifted to Enola, or to pre-blocking moves further west/south.

I'm honestly unsure whether this will last: recent PSR implementations are full of yard reopenings, and Enola isn't an efficient facility, but thus is the story of this region.

The Q I have in the longer term is how relevant carload traffic is to NS’s long term plans for the NE. They’re down to one mixed freight per day to/from northern NJ; the network is really intermodal-heavy. If carload traffic continues to decline, that’ll also reduce constraint