NYC Subway Signaling - A Decade of Change

Ten years ago I was provided with a amazing PDF document from the New York City Transit Authority that contained diagrams of every rail line, every rail yard and every interlocking on the Subway, Staten Island Railroad and even some railroad shotlines. The interlocking diagrams themselves had details from switch and signal numbers, details regarding the control panels and interlocking machines and even the date of details of the contracts that the signaling equipment was installed under.

Since then the NYCTA has been pushing hard to eliminate the last bastions of single interlocking towers with CTBC projects ongoing on the Flushing and Queens Boulevard Lines.  As my document aged I attempted to get an updated copy, but was told that the NYCTA was annoyed that the first consolidated document had ever been created and that the information had been effectivly split up between all the various line managers.  I don't know if that was true or not, the NYCTA culture thrives on control of information (often using "terrorism" as a justification), but while searching for some photos of the old E 180th St tower to fix a dead link I came upon a 2019 version of the same document.

Because nobody had metaphorically slipped me the new version "under the table" with a promise of confidentiality, I am just going to link both documents here so you all can see for yourself the extent of signaling heritage that has been lost on the NYCTA over the last ten years.  Enjoy.

NYCTA Schematic Track and Interlocking Diagrams 2009
NYCTA Schematic Track and Interlocking Diagrams 2019

DART - One System, Two Methods

Dallas Area Rapid Transit is one of the new generation of North American light rail systems, as large in scope as many heavy or commuter rail networks, but built to a much lower price point.  DART was built in two waves, the initial Blue and Red lines built between 1996 and 2002 and then the Orange and Green lines built roughly between 2010 and 2012.  Despite being part of a unified transportation system, DART uses two completely different signaling methods.

 Signaling on the Red and Blue lines consists of pretty standard ABS CTC with wayside signaling.  Signals consists of single direction stub masts placed back to back.  An ATS capability is provided via some sort of IIATS or Westcab transponder to enforce signals displaying Stop, however track speeds are not enforced.

Interlocking signals use a NYC Subway style system with the upper head indicating block state and the lower head route.  Thus G/Y is diverging clear and Y/G is approach straight.  Also note the use of traditional track circuits with impedance bonds.

Of course for the second phase Orange and Green lines, DART decided to switch gears and adopt a cab signal system without fixed wayside signals.  Cab signals are of the jointless audio frequency type and signals are only provided at interlockings with the ability to display Stop (R), Restricting (R/Y) and lighted directional arrows for everything else.

These directional signals were also used in the Phase 1 street running portion downtown, so it was natural to reuse the system in cab signal territory to reduce the need for re-training.

Unfortunately my photo of the cab signal display did not turn out, but there is not a lot of complexity.  The operator sees the vehicle speed in red LED and a target speed in orange LED.  The speed changes as soon as a new cab signal code is received with an ATO style brake application being instantly applied, as opposed to a penalty application after a grace period. This system enforced both track and block speeds with speed control in 5 or 10 mph increments between 10 and 60mph.

It was interesting to see these two generations of systems running side by side with Orange line trains in particular starting under one system and finishing under the other.  It was also interesting to see how much train operation was being impacted by the speed enforcement with operators having to brake about 5mph past the speed target and then re-accelerate.  This created a very jerky form of operating where as the lines without speed enforcement saw much smoother operation.

Although many light rail systems are adopting or converting to heavy handed forms of train control, there are still many systems built since 1990 that have retained lower cost, human-centric signaling systems that will likely be the last such examples as heavy and commuter rail lines become increasingly "supervised".

EDIT: DART actually has a THIRD method of operation that I discuss in a followup post.

Thinking About the Price of Safety

I have been a pretty vocal critical about the value of PTC when it comes to general rail safety.  It's the sort of thing that sounds great in practice, but looking at the number of lives lost in PTC preventable rail accidents the costs are seriously hard to justify.  Anyway, in this day of weighing the cost of hundreds of thousands of lives lost due to a pandemic against the severe cost of an economic depression, the folks at 538 took a crack at trying to figure out how much the government should spend to save a life.  It provides some additional metrics beyond "lives" or even Quality Adjusted Life Years that get to people's own subjective valuation of risk.

Right Hand Rule - How De-Regulation Ruined US Signaling

Why the US railroads seem to go from having a pathological need to mount their signals to the right hand side of the tracks they governed, like this...

Or this...

Or even this...

To, seemingly overnight, just doing this...

Well in 1939 most locomotives provided the engineer with visibility like this...

So in 1939 the ICC decided to legislate the obvious and required that all railroad signals be situated to the right hand side of the track they governed.  Of course the usual system of waivers and grandfathering applied so that left hand running lines such as the CNW didn't have to rip out its fireman-side signals, but all of that created barriers to cost cutting, even after the 1960's rolled around and all of the main line steam locomotives had been retired. 

By the 1980's, chopped short hoods on the F end had been the norm for the better part of two decades with only a few out-layers like the Southern, still holding on to the practice.  In 1985 the ICC successor, FRA decided that the Right Hand Rule was obsolete and railroads could put signals on whichever side of the track they wanted. 

  

The effect was immediate with back-to-back masts replacing split masts automatics and end-of-siding signal bump-outs becoming some sort of vestigial organ. Bracket masts, the go-to low cost option for bi-directional automatics on two track main lines were hit particularly hard along with the two track automatic signal bridge.  Multi-track cantilever signals have hung on, but only in areas of restricted visibility like curves.

Now in Europe many of the right (or left) hand replacement requirements are either still in force or at least still practiced by the state owned railways and as such there is much more diversity in the signal mounting systems, typically in the form of signal bridges.  It just goes to show how important the regulatory environment can be for something as esoteric as signal diversity.