Higher capacity signalling

[stephenk]

From information I can obtain (from the previous timetable) 28 trains per hour per direction (tph) were run between Roma Street and Bowen Hills during the busiest hour of the morning peak. The most per track was approx 15tph, which equates to a train on average every 4mins.

Paris RER Line A introduced an overlay in-cab signalling system called SACEM. This allows trains to drive closer to the train in front at around 30kph in the station area, using very short signalling block sections. This allows for 30tph to operate, with equates to a train every 2mins. This is allowing for maximum 50sec station dwell time. This system is overlayed on top of the existing signalling system, so it is possible for non-equipped trains to operate over the same tracks (but without the closer spacing to the train in front). SACEM and it's variants are available from various signalling manufacturers, and is also the signalling system used  on the Hong Kong MTR in it's automated version.

I think that this solution would be great for QR to increase the capacity through the central area of the Citytrain network. Allowing for 1min20sec dwells, would allow for 24tph operation, a train every 2mins30secs. Taking into account the two tracks per direction in the central area, this could allow for 48tph, an impressive 20tph more than at current levels! Even with 20tph per track allowing for more operating margin, would allow for 40tph, an improvement of 12tph.

The biggest operational hurdle involved would be the many at grade junctions on the Citytrain network, particularly around Roma Street, and where trains switch from main to suburban lines. Some infrastructure changes including flyovers and flyunders may be required, but would be difficult at Roma Street. Increased stabling away from Mayne would maybe reduce the number of "other line" crossings required, and also allow for stabling of the extra trains required to run the increased service.  Also as frequencies could be increased on the branches then more road level crossings would have to be converted to bridges. Junction operation would have to be changed to more efficient  method of getting trains through such as first come first serve operation (I often have to wait in an on time ex Ferny Grove train outside Bowen Hills to allow a late running train from another branch through).

I would rather an extra tunnel was dug through Brisbane to increase Citytrain capacity to allow for metro services to much of the network (10mins max gap), but if that didn't happen or was delayed (as the state government appear to prefer digging road tunnels instead), then improving the signalling would be a reasonably cost effective way to utilise the existing infrastructure.  Of course, a new tunnel and improved signalling would be even better!!

[ozbob]

Good points Stephen.

One of the things that makes the figures look a little misleading was the dwell times at Central (often 5 minutes) for many services.  In 2006/2007 there was a major upgrade of signalling Normanby-Roma St - Mayne. This involved replacement of the existing relay based signalling system at Normanby with a MK3 Solid State Interlocking system, together with a significant signalling upgrade.  Electric suburban units can be queued quite close these days due to these systems.

One issue is the need to run long trains (freight and passenger) through the system. 

A western by pass line for freight would free up the Exhibition loop and the central city rail axes generally and then could be run as a metro.

I think the major constraint at the moment is simply the lack of trains per se, rather than signal capacity limits. I have observed one train entering Roma St platform as the the proceeding train has just left with a very short interval (30 seconds or so).

As the number of trains increases signalling systems you describe may well be needed!

There is a study underway at the moment looking at underground rail extensions.  Merivale bridge is fast approaching  its limit too.

Cheers
Ozbob

[stephenk]

Certainly if capacity is to be increased significantly through the central area then extended dwell times at Central will have to be reduced.

The existing signalling supports a minimum dynamic headway (time between wheel start of departing train and wheel stop of arriving train) of 75-90secs at most central area stations. A system such as SACEM could support approximately 60secs (and maybe even slightly less) dynamic headways.

Some examples of suburban line capacities (per track) with modern signalling that Citytrain should aspire to:-
Paris RER A - 30tph
Tokyo Chuo Line - 27tph (and reverses all trains at just a 2 track terminus!)
Tokyo Yamanote Line - 24tph

[mufreight]

More track capacity is the answer, improved signaling systems can help but the key govening factor is station dwell times, something that can be improved by things such as platform heights level with carriage floors and a third door in each carriage to enable faster loading and unloading.

What is needed realisticly for more system capacity is more track, with the present Government and local authority preoccupation with tunnels a new rail tunnel branching off the Coast line at Dutton Park and off the Clevland line at Buranda running underground to stations at Wooloongabba, Gardens Point (Parliament House) Central Railway, Spring Hill Joining the Exhibition line with a new station to serve the Royal Brisbane Hospital and the Exhibition at Bowen Bridge Road, this works out as about a 6km twin tunnel line requiring few if any resumptions, removing the bottleneck of the Merivale Street bridge, enhancing the city network and the increased capacity through the city would provide extra paths for increased services on all lines.

Have a look at the map, your thoughts please 

[brad C]

There are also a raft of driver responses to consider with any type of signalling.
It is interesting to note driver responses to double yellow signals, which are ostensibly green with the old 'close up' which were used on the northside automatic sections prior to electrification. As soon as double yellow is spotted, some of our overcautious drivers start to apply the brakes. Very frustrating descending the dakabin bank in the mornings with the 100kph speedboards.
The other big problem is Bowen Hills with crew changes and sometimes admission to the stabling yards, which can sometimes see trains banked up to Brunswick Street of a morning and evening.
On the matter of stabling yards, since the July 07 timetable changes, we see a larger amount of empties returning to mayne of an evening and less stabling at big yards like Caboolture ( 11 lines) and Ipswich (8 lines) Why is this so???
Brad C

[Derwan]

I don't think much can be done to increase signal capacity in the city.  Signals are basically just over a 6-car train-length apart.  Often my train arrives at the end of the tunnel at platform 6 before the previous train leaves the platform.

Additional platforms would help if possible at Central - so that each would work like 1/2 and 3/4 - where a train can arrive before the previous one leaves.  Platforms 5 and 6 currently don't allow for that.

It may be possible to improve signalling outside the city centre.  One particular example is inbound at Toombul on the left track.  The signal is just past the platform.  My train runs express in the morning - but often has to wait for an Airtrain to cross in front of it.  There are a few hundred metres of track between the track to the airport and Toombul station, but no signals.  To avoid confusing passengers waiting to board at Toombul, the drivers slow and if necessary stop just before the platform.  Even trains doing a stop at Toombul have to slow significantly to avoid overshooting the platform and running a red light.  The signal needs to be moved further towards the airport track or another signal needs to be added.

With regards to drivers slowing at double-yellows, I believe this is what they're supposed to do.  The idea of the double-yellow is to allow for trains to run closer together.  A double-yellow means 2 or 3 signals from a red  - which would probably equate to a distance that's no more (and possibly less) than that between a yellow and red outside the 4-aspect signal area.

With regards to stabling yards - I read somewhere (probably on here) that they were moving more towards centralising the stabling to reduce vandalism of the trains.

[stephenk]

I don't think much can be done to increase signal capacity in the city. 

Yes there is! You can get a 30sec dynamic headway improvement with cab signalling systems such as SACEM.