No Approach! The Duality of Uncommon Signals

We all learn about traffic lights in elementary school.  Red means stop, green means go and yellow means slow or caution. These are the basics of automatic block signaling that also tend to get taught in entry level railroading books. Now its pretty logical that a signal might lack the ability to display a clear indication. A permanent stop condition or the end of automatic block territory are both situations where a Clear signal would not ever apply. However there are a few situations where signals in North America can display Stop or Clear, but not Approach on the full speed head. 

The first is at interlockings outside of automatic block territory like a diamond crossing or drawbridge. The signal provides movement authority through the interlocking and without track circuits outside of the interlocking limits there is no "prepare to stop" points an Approach type signal would apply to. Trains will have their own movement authority like a track warrant so a clear signal is basically the interlocking telling the train "you do you". One might expect signals in this case to display a Restricting indication, instead of a clear, and sometimes they do, but that is going to come with a 20mph speed restriction, or less, which can be a time hit on unsignaled lines with higher track speeds. 

The next situation, Manual Block territory, would be very familiar to those in other parts of the world. Although almost extinct in the US, there remains a bit of manual block still in service on the LIRR and the way to identify a manual block signal is the lack of an approach indication. (This also applies in general to historic PRR signaling charts.) Signals will display Stop or Clear Block with any Approach functionality handled by a separate distant signal towards the end of the manual block. The PRR even went one further sometimes substituting the \ "Caution" indication in place of / Approach. 

Sometimes its really not good to have locomotives stopped and waiting at a specific signal,  Maybe there's an issue with a grade crossing, or noise, or diesel exhaust. In this case it would not be desirable for trains to approach that signal prepared to stop, so a preceding signal will either hold trains short or allow them to approach a signal with some sort of proceed indication. The most notable of these is at the entrance to Washington Union Stations 1st St tunnel that the currently diesel hauled northbound trains cannot enter without having a signal displayed further on that allows them to leave said tunnel. Another nearby signal location at CSX's LENFANT interlocking might lack southbound approach signals for a similar reason due to an overbuild.

One somewhat PRR-specific situation is where interlockings are provided with exit signals and because of the short distance between the interlocking's entrance signal and exit signal, Slow Approach is used instead of Approach. This creates an upper head that can only display --- Stop or | Clear. The C&O also made frequent use of exit signals, but seemed to keep their upper head Approach indication, although Medium Clear to exit Approach allowed the C&O to minimize the use of R/Y/Y/ Medium Clear.

A fairly new situation where Approach has been "omitted" involves high speed turnouts. At certain points on the NEC, Amtrak has decided to combine a flashing green "Cab Speed" signal indication with R/*Y* Medium Approach. At the end of a main track that converges into another via a high speed turnout, the result will be an upper head with green and red lamps/positions and no yellow lamp/position.
 

The Enthusiasts Step Up

Unlike Europe, Heritage railroads in the United States never developed a vintage signaling component beyond what one might describe as display items. The big reason for this is that in service signaling and interlocking appliances have significant regulatory inspection, testing and documentation requirements that are beyond the reach of most tourist train operators. The result has been that most preserved towers are completely inert, with just a handful having interactive elements such as operable interlocking machines (SS43 BERK) or full on simulations (HARRIS). However, in recent years it seems that the private collector/enthusiast space has been stepping up to fill the gap as exemplified by the small YouTube channel Laser 711.

Signal and signaling equipment collectors have been around for some time, snapping up such items as model boards, CTC cabinets, full size signals and even interlocking machines. Until recently, railroad signaling departments would tend to keep their retired equipment, as similar vintage hardware was still broadly in service and the parts to maintain them were no longer being manufactured. However, the PTC related re-signaling push rapidly phased out so much of the relay era railroad signaling that the equipment is now being sold for scrap or offered free to anyone with the capacity to haul it away. 

In the context of interlocking towers, model boards and CTC cabinets have been widely collected for some time as switch to video display in a dispatch office had long ago destroyed their reuse value. Somewhat ironically, it was the older mechanical and electro-mechanical interlocking machines that retained the most value as a source of spares for their kin.  (For example a major reason LENOX tower near St. Louis was closed was to supply parts to the CNW LAKE ST machine in Chicago.) However as the number of these in service interlocking machines hit zero, anyone with a large enough truck could cart the survivors away for their own personal amusement. This is where Laser 711 comes in, having apparently set up not just a HARRIS style PLC backed simulation, but the full hardware stack including relays, point machines and signals.

 He has also restored an ex-Erie CTC console from BK tower along with its original code system, and now appears to be in the process of implementing as much field functionality as possible "in relay".

Of course it would be great if more publically accessible museums were able to step up to the plate with functional period correct signaling equipment, but the signal enthusiast community, powered by recent advances in the "maker" scene and high capacity pickup trucks, seem to be taking up a lot of the slack. Just like we have seen with the extensive telecom switch collection of Step by Step Phil, these private efforts stand a good chance of eventually finding their way into durable preservation.

Attempted CTC at the Seashore Trolley Museum

I will also mention that non-FRA regulated streetcar/transit museums have the best capacity to implement "live" historic signaling. When visiting Shoreline Trolley Museum I was shown their "in-progress" CTC system that they were building from thousands of relays donated by Amtrak and Metro North.

 

The fact that I have not heard much if anything about that project in the past 20 years hints at its priority in the greater scheme of things, but all it takes is the right team of enthusiasts to get a project off the ground.