Saturday, November 16, 2013

Sector 2 Train Timetables - Designed for 24tph?

Is 24tph across the Merivale Bridge possible?
Whilst researching the previous blog posts, BrizCommuter picked up on an interest way that the service patterns are designed in the sector 2 train timetables. BrizCommuter was expecting the timetables to based around a train running through the CBD every 3 minutes/20 trains per hour (tph) as per the sector 1 train timetables. However, this isn't the case...

The sector 2 train timetables are based around a repeating 2/3/2/3 minute service pattern, although in many cases as not all potential track slots have be filled, it is a repeating 2/3/5 or 3/2/5 minute pattern. Given that trains cannot realistically run closer than every 2.5 minutes, BrizCommuter suspects that this is actually a repeating 2.5 minute/24tph service pattern, and that the printed timetable simply does not show the half minute. This is not confirmed, but has been assumed for the rest of this blog post. If it is not the case, then it certainly should be!

It appears that no more than 18tph will actually be operated through the CBD (Park Rd to Bowen Hills) in the sector 2 timetables so why do we have a service pattern based around 2.5 minutes/24tph intervals  instead if 3 minute/20 kph intervals:
  1. It allows for more regular scheduling. With 3 minute intervals, the Ferny Grove Line would have an uneven alternating 6/9 minute frequency. This would result in uneven loadings. With a 2.5 minute interval, the Ferny Grove Line has a regular 7.5 minute frequency (shown as alternating 7/8 minute frequency. 
  2. It allows for more flexibility. Additional services run in each 15 minute cycle on either the Gold Coast or Beenleigh Lines. However, they optimally require different slots in the 15 minute cycle through the CBD. This would not be possible using 3 minute intervals without slowing down journey times, but is possible using 2.5 minute intervals. 
  3. It may allow for an ultimate capacity of 24tph through the CBD, the limit with current signalling (with minimal margin for delays). This would allow for 8tph to be run in the peak direction on the Gold Coast Line, as well as 8tph each on the Beenleigh and Cleveland Lines. However, to allow this to be possible would require more trains, stabling for those trains, and more infrastructure (such as Coomera to Helensvale duplication) on the Gold Coast/Beenleigh Line corridor, all of which cost $$$. For reliable operation at 24tph, improved signalling may be required. 
  4. Until (3) occurs, the timetable will allow for at least 2.5mins of additional operating margin (delay catch up time) per 15 minute cycle. 
To conclude, it appears that the timetables are based around 2.5min (or alternating 2/3min) intervals. Whilst ultimately this could allow for 24tph operation, until there are sufficient trains, tracks, and signalling to allows 24tph to be operated reliably, then the service pattern will just allow for more flexibility in scheduling to cope with the 7 lines that share the sector 2 changes.

Update 05/12/2013

From insider information, it is likely that points 1, 2, and 4 are the case with current infrastructure. With a maximum capacity of 20tph, only one additional Gold Coast or Beenleigh Line (but not both) train can be operated per 15 minute cycle.


  1. So, are you saying that we could have had more trains with the current level of infrastructure?

  2. No - more train services would require more infrastructure. For more than an irregular 6tph Gold Coast peak, the Coomera to Helensvale would need duplication. For 4tph off-peak to Gold Coast and Beenleigh would the require above, plus quadruplication between (roughly) Sunnybank to Kuraby.


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