Signals are Key

Dutch Infrastructure operator ProRail has been looking at Japanese railway practices for some time now, in an effort to understand the „secrets” behind their efficiency and see how these could be applied at home. In fact they had their „man in Japan” spend a year there and posted regular reports on his findings on their intranet. In a recent presentation to the IRSE Dutch section, Vincent Weeda (ProRail) and David Koopman (DHV) explained a concept they call „Kort Volgen” which literally translates as „rapid following” and is all about shorter headways and less complicated lay-outs. Something that should be very familiar to those of us involved with rapid transit systems.
To start it off, some observations about Japanese performance were given:
• On many (sub-)urban lines a slow train and an intercity service, both at 10 minute intervals is operated
• In and between cities large numbers of passengers are transported
• 97% of trains operate at less than 5 minute delay
• In busy spots a train stops at a station every 2 minutes
• Signals passed at danger are extremely rare
• In most railways fares have not been raised since 1987
• Railway companies operate both infrastructure and trains and are profitable
No wonder ProRail, which has enjoyed less than favourable reviews of its performance by both passengers and parliament off late, are asking themselves „How do they do it?”. The answer it turns out is surprisingly simple and has nothing to do with our traditional perception of white-gloved drivers, miraculous quality management practices and rigid discipline. The secret formula is keeping things simple and focussing on the essentials. Not necessarily as an integrated railway, but as a business. If you want to make more money, you operate more trains and transport more passengers. That in turn requires more capacity and an unobstructed flow of traffic.
1. One of ProRail’s first observations was that „Signals are Key to Everything”, always something that goes down well with an IRSE audience.
2. Optimum traffic flow requires signals to be spaced at short distances, if needed 100 meters apart, so every train releases its route for a next one quickly.
3. A smooth flow of traffic even when trains bunch up, and speedy recovery of perturbations also requires short signal spacing.
4. In designing a line, signal placing should be as restriction free as possible.
5. Speed is essential, but avoiding slower speeds is more important than high maximum speeds.
6. Short dwell times are essential, as are rapid turnaround times at terminal stations.

Signal Placement

That’s really all there is to it. Of course the Japanese also have their stabling yards, depots and workshops and the tracks and point work to get to and from them. But first and foremost, the principle is to keep it simple and concentrate on the essentials. All frills cost money, require maintenance and are a source of disturbances. „If it’s not there, it can’t break”. And therein lies the lesson for our railways it would appear. In contrast, Vincent points out that Dutch requirement specs for a layout read like long wish lists with endless restrictions. Some of the examples quoted are:
• Additional point work for various scenarios to handle disturbances.
• Additional crossovers to cater for possible future timetables.
• Bi-directional working on all tracks, even when four tracks are available, to overtake defective or slow trains.
• Braking distances based on worst-case performance of each and every train (as designed decades ago).
• Maintaining existing functionality.
• Future proofing of everything.
Of course all these requirements have their backgrounds and historic justifications. But together they result in overly complex systems, the consequences of which are seldom analysed. In short it leads to a very expensive infrastructure, which paradoxically is hardly able to deliver the required performance anymore.
So how does this affect signalling? The engineers sent on the study trips to Japan noted that the Japanese had no qualms about placing a signal almost everywhere, including places where Dutch engineering rules would never allow this to be done. Examples are directly in rear of the platform, just in advance of a level crossing, after a set of points etc. Secondly the layout appeared much less complicated, with almost no bidirectional working, much less points and crossovers and much simpler station throats.
When they discussed our engineering rules with their hosts, the simple question returned was „but how can you possibly position a signal anywhere then?”
In adopting the Japanese principles, the first rule of thumb was “just position all the signals you need to optimize traffic first, and let the other technical systems follow from there” (as opposed to today where e.g. an overhead sectioning or level crossing can prevent optimal signal spacing). And „don’t worry about trains stopping at inconvenient locations too much. Just make sure they can move on quickly instead”.
Short signal spacing in the direction of travel, is another example. In Holland, bidirectional working is required virtually everywhere. But what does it really get us, is the question Vincent asks. In disturbed situations, following an accident, more often than not, both tracks are blocked. If we want to drive past a stranded train, we disturb the traffic in the other direction and defective trains can (or should be able to) be removed fairly quickly anyway. It is an eye-opener to see how much simpler the layout becomes if we abandon bi-directionality. Signal placement is simplified dramatically, control systems and algorithms become simpler, drivers and signalmen have better overview and situational awareness etc.
A typical Japanese layout has much less points than ours. Points can give flexibility in disturbed situations, although „ only to a degree” as pointed out in the discussion of the benefits of bidirectional working. But this flexibility comes at a price. Points eat capacity, as they limit signal placement options and usually introduce speed restrictions. Not just when traversed diverging, but also due to induced cant limitations, standardization of point types leading to requirements to apply only in straight sections of line etc. They impose restrictions on timetables, as they have to be traversed and require de-rusting movements to be made regularly, offer the possibility for misrouting, require inspections and scheduled maintenance. They are an inherent safety risk, subject to wear and tear themselves but also cause wear to rolling stock etc. And in the Japanese philosophy one should avoid the need for, rather than employ the option of rerouting.
In employing these different „system philosophies”, the potential for simplification and cost saving appears to be enormous. Compare Tokyo and Utrecht Central stations. Both have a similar number of platforms and a comparable role in the network. Tokyo Central has 28 points, Utrecht Central has 280! Both stations have uncoupled the main traffic streams to eliminate crossing moves as much as possible. At present Utrecht handles 60 train movements per hour, Tokyo handles 180.
In Holland most stations have a generic speed limitation of 40 km/h within the station limits. This is due to the nature of the Dutch ATP, but also to limit the number of point type and space taken up by them in the complex station throats. If we could raise the lower speeds on the network first, or instead of concentrating on higher speeds, that would optimise traffic flow as well as benefit both slow trains and InterCitys alike. And it avoids the capacity penalty usually incurred when the speed differential between train types is increased.
Early traffic simulations by the study group showed that this concept has promise and now the studies are being extended to the SAAL (Schiphol-Amsterdam-Almere-Lelystad) corridor upgrade project.

Simulation results


As an example, one simulation showed that the simple addition of a signal directly in rear of a platform on a station on the open line and leaving out the cross-overs traditionally found in such locations, still respecting all other design constraints like braking tables etc. would increase theoretical line capacity by some 29%. Most readers will note that this is a very common practice in rapid transit systems as it allows train to ease up to the platform and the train they are following is departing, usually referred to as platform re-occupation time. Further studies taking into account optimised braking tables etc. show even greater promise but are likely to require some more thought on the implications for safety cases when combined with the limitations of existing ATP systems. This of course led to a debate on the benefits ERTMS level 2 might deliver in such system concepts.
Any signal engineer worth his salt will undoubtedly be able to point out many potential issues with the „kort volgen” concept and the Dutch section audience was no exception. „How many Yellow signals will a driver encounter in rear of a red signal”? „Where do we get the additional ATP codes”, etc. But isn’t the real challenge to our profession to investigate under which conditions a number of these benefits can be had, as they apparently are in Japan? And why not examine how we can pick the „low hanging fruit” quickly instead of waiting for ERTMS to be rolled out as an enabling technology. And „adopting 1954 engineering rules to ERTMS design has already been shown to deliver just about no capacity benefit at all”, as one of the members in the audience remarked.
We are perhaps left with the question „can it really be that simple”. And if it is, why hasn’t it been tried before. And the obvious answer might be that it has, and successfully as well. In rapid transit and urban railway settings. So the real issue might be to adopt these principles on mixed traffic lines and break out of the heavy rail design paradigm. It will be interesting to see how this develops and observe a possible application to the SAAL project.

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One Response to Signals are Key

  1. Pingback: Otros mundos ferroviarios. Japón (II) | ruedaycarril

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