I find myself playing with railroads a lot (I am originally from Chicago, so it’s appropriate). I have to deal with people who actually know what they are doing, while I have been getting by on bluff and bluster and the general knowledge that the important thing is to keep the train centered on the tracks. Thus, I’ve been reading railroad books on the side - so I can bluff better.

I thought this would be dull but important, but it turned out to be interesting and important. It’s something of a compromise between a technical manual on the history of signaling and a coffee-table book with attractive train pictures; the author manages to pull this off.

I am attracted to books with lots of “trivia”: facts that are esoteric, unexpected, and slightly amusing. Thus:

Early trains were routed solely by timetable. There wasn’t even telegraph available yet. Needless to say, there were some spectacular accidents. But since brakes didn’t work all that well it wouldn’t have mattered much if a signal indicated another train - you probably couldn’t stop in time anyway.

The expression “to highball” comes from one of the early American signaling methods: hoist a red ball on a signal pole if the track ahead was clear.

The early railroads in North America and Europe all had their own signaling methods, once it became obvious that signaling was a good idea. A spectacular accident on one of the British railways (The Great Western?) resulted in The Government getting involved and dictating signaling uniformity. As in many other cases when The Government tells people to do stuff, this was initially successful but had the long-term effect of inhibiting progress on new signaling methods. Thus most of the improved signaling technologies (automatic blocks, for example) came from North America, where railroads were free to have spectacular accidents without Government interference. It was instructive that all the examples of historic signaling methods (manual interlocks, the “staff” method”) shown in this book came from British and Irish railways where they are still in daily use.

Manual interlocks are what you see in historic photographs of rail yard operations. These are large levers set into the floor of a control tower that a signalman has to grab and pull to throw a switch and/or set a signal. In the early days, these were entirely mechanical - there was a control linkage connecting the lever in the tower to the switch or signal, often several hundred feet away. It took muscles to be a signalman back then. Eventually the linkages were replaced by pneumatic, hydraulic or electric assists. There are some nice pictures of a still-operating manual tower on Irish Rail. In yards with complicated switch setups, the manual interlock levers often had to be thrown in a particular order, to prevent switches from being set up in dangerous alignments. There were also timers connected to the switch levers, to reduce the possibility of switches being thrown while a train was passing over them. Thus if you were a signalman at a yard and you needed to let a through train go through, you would have to throw the switches in the right order to let the train bypass occupied track, and once you threw those switches the timers would prevent you from setting them back. Therefore, making a mistake was a very bad thing - the train would have to stop and wait until the timers released and the switches could be reset. This was another reason for requiring the switches to go in a specific order; the last switch to be set is the one controlling the signal for entering that track block; thus the oncoming train can’t enter the block until all the switches are set properly.

I had no idea what the “staff” system was, but not only is it still in use on Irish Rail, there are also couple of branch lines in the US that still use it. The train stops at a control tower and gets a “staff”, which is a physical hunk of wood or metal inscribed with the name of a track section and with a series of grooves or bars that act as a “key”. Possession of the “staff” allows the train to use that track. When the train reaches the end of that track block, it returns the “staff” to the control tower or station there and picks up another “staff” for the next section. The obvious problem is that the system depends on two-way traffic flow; there has to be a way to get the “staff” back to the original station. There was an ingenious mechanical solution to this in Europe - the invention of interlocked staff-dispensing machines. A dispensing machine has a number of staffs but only releases one at a time. A train crew picks up a staff from the machine, does its run through that track block, then stops and inserts the staff in the machine at the far end of the block. (The “keyed” nature of individual staffs prevents using a staff for the wrong track block). This sends a signal to an interlocked machine up the line that allow that machine to again dispense exactly one staff. Thus you could have several trains going in the same direction, each secure that it had “the” staff for that track block. As long as the overall number of trains using the track block balances out by direction, the dispensing machine won’t run out. Obviously automatic blocks would have been much simpler, but they were Not Invented Here.

The automatic block system depends on the train completing a circuit between the rails. Because steel rails and steel axles aren’t the best electrical conductors, there are sometimes problems with very short trains on days with bad weather that requires sanding the tracks. Hyrail and track maintenance vehicles also sometimes fail to trip automatic blocks; this has resulted in some ugly wrecks. The setting of a train signal is called the “aspect”; railroaders thus talk about the “proceed aspect” rather than the “green light”. A trackside signal mast will often have two sets of signals - one has the aspect for this block; the other has the aspect for the next block. This allows a train crew to start slowing down for the next block if necessary. If signals are arranged vertically, they are the opposite of highway traffic lights - the green signal will be on top and the red on the bottom. This is considered to contribute to “fail-safe” operation; the upper signal will act to partially shield the lower signal from snow and ice accumulation.

I had no idea that most European railroads have positive interlocks with grade crossing signals. In the US, it is up to a motorist or pedestrian at a grade crossing to avoid trains (although the train crew must sound a horn or bell when approaching a grade crossing). There may be a gate or barrier, but that is not connected in any way to track signals. I expect the system evolved that way here because the track usually came before the road. In European practice, grade crossing signals are fail-safe connected to track signals. If a grade crossing light or barrier isn’t working, the corresponding signal for that track block will revert to “STOP”. There are a horrendous number of grade crossing accidents in the US every year even with American drivers; I pity European visitors who blithely cruise through a grade crossing with nonfunctional signals only to find themselves decorating the front end of a locomotive.

The future of rail signaling will probably be something already under test - Precision Train Control. Paradoxically, this does away with trackside signaling altogether. Each train has a GPS and a radio connection to dispatch and follows instructions. Although it seems scary to eliminate signaling, this is essentially the same way air traffic control works. The railroads feel that PTC will allow them to scrap a lot of maintenance-intensive signals and move more freight on less track. We’ll see.

The only minor flaw I find with the book is that I would like to see more technical diagrams of how signals work and fewer pretty color pictures of signal towers at sunset. Some illustration of accidents caused by signal failure would also be instructive. However, my overall impression was quite favorable. ( )