Better signalling = more trains. How moving block signalling could boost capacity across Melbourne’s rail network
New thinking is signalled for Melbourne’s transport woes
Our State Government is now driven by a vision drawn from Los Angeles. The East West Link promises not merely to increase levels of car and truck traffic and pollution. Worse, it will guarantee there are no funds available to improve transport for decades.
Meanwhile, such official backing as has existed for public transport has focussed almost exclusively on the 9km ‘Melbourne Metro’ rail tunnel. While undeniably a more worthwhile project than the East West Link (and with a higher benefit-cost ratio) the Metro tunnel has monopolised public transport planners’ attention to the point where it has all but blinded them to the existence of less costly but more beneficial improvements.
The Metro tunnel is promoted as the ‘magic pill’ solving every problem with the rail network — a claim it cannot possibly live up to in reality. To rationalise the single-minded devotion to tunnels, planners within PTV have got into the habit of claiming it is a prerequisite for virtually any other improvement — even when it bears no logical connection at all!
The rail network would benefit substantially more from measures that bring it up to date with the state of the art in European urban rail systems. A good benchmark is the Paris ‘RER’ suburban network, which shares many features with ours: it operates on double track, with lines that combine in the city but branch into three or four parts in the suburbs. One difference is that the RER operates double-deck trains, which makes it vulnerable to dwell-time issues at key stations at least as severe as ours.
Yet the RER is able to schedule trains reliably every 120 seconds in peak hour — a feat said to be impossible here. Actually, until a few years ago it wasn’t possible in the RER either. Then the Parisians rolled out a key capacity-boosting measure: described technically as “moving-block in-cab signalling”.
This short video from London explains the benefits and technical details behind moving block signalling (alongside other technology such as Automatic Train Operation and platform doors).
Moving-block signalling explained
Trains on rails do not operate like trams or cars on roads. Because they’re so much heavier, they require longer distances to stop, so it isn’t safe for drivers to rely on sight to keep a safe distance, as a car or tram driver can. Instead, drivers rely on signalling that tells trains when it is safe to proceed. The technical attributes of this signalling are the key factor that determines how many trains per hour can run on a single track.
Melbourne’s ‘fixed block’ signals were standard for rail systems through most of the 20th century. Imagine a road with traffic lights every 500 metres, where a car can proceed into one of these 500 metre ‘blocks’ when the light turns green, but then the light turns red, and does not turn green again until the first one has cleared the block. With such a system the traffic capacity depends critically on factors like block spacing.
Our highest standard currently is 2-minute fixed block signalling. This has a ‘theoretical’ capacity of 30 trains per hour, but because running times vary randomly, the ‘practical’ capacity is about 80% of this, or 24 trains per hour. On suburban sections of many lines (such as to Dandenong) the signalling headways are longer, permitting just 16–20 trains.
Moving-block signals are a big improvement, operating more like the way cars follow each other on a motorway. The system monitors the distance between trains and issues signals to the driver whether it is safe to proceed at full speed, or if it is necessary to slow down or stop. Effectively, the signal ‘block’ moves with the train. The signals are issued in the driver’s cabin rather than with trackside lamps, hence “in-cab signalling”.
With this type of signalling — now available off-the-shelf from a number of suppliers — it becomes possible to reliably timetable trains 2 minutes apart or better on the same track. Paris manages this well. It is also being installed on the London Underground, where the Victoria Line now operates 33 trains per hour — and anyone who has been to Kings Cross knows the crowd management problems there are every bit as challenging as they are at Flinders Street!
In Melbourne, the likely capacity improvement is at least 50%. This is capable of being achieved on every line in the system at an estimated cost (based on estimates from suppliers) of between $1.5 and $3 billion. By comparison, the $5 billion to $10 billion Metro tunnel provides more capacity on just two groups of lines. New signals also provide the additional capacity to fit Doncaster trains on the existing line to Victoria Park: the Metro tunnel does not.
To obtain the full benefit some additional infrastructure upgrades will eventually be necessary, the foremost being level crossing grade separations. The important thing is to not be limited in our thinking when it comes to effective alternatives.
The above article is from the July 2013 PTUA Newsletter. Join now to get regular newsletters.