Signalling & CBTC

[somebody]

I don't see the advantage of having trains following more closely without significant infrastructure upgrades.

Let's look at the mains through the city.  No matter how close a train is behind another train, it still has to wait for the one in front to leave a station.  Then by the time it's done its stop it has a clear track in front.  No close-following required.

The only time this would be an advantage is if every platform set-up at every station was like the suburbans at Central (and no doubt like a lot of the platforms at Roma St but I'm less familiar with that station).  This would allow two services to be stopped at the same time and then depart more quickly after each other - then do the same at the next station.

So to see any improvement with better signalling in Brisbane, I think you'd need 2 more platforms at Central and 4 more at Fortitude Valley and Bowen Hills.  CRR stations would need a similar set-up.

Amplifying on what BrizCommuter has said, the bifurcation arrangements at Central would actually reduce the benefits of the advanced signalling.  This is because it is two solutions to the same problem - one is addressing headways from the dwells, the other is reducing headways from the train separation.  The bifurcation removes the headway constraint shortly after the train ahead has cleared the points and entered platform 1-4.  Two problems are that platform 4 has an awfully slow entry, and for some reason the crew changeover in peak didn't move to Central, so the execution isn't brilliant

[colinw]

Simon.  You have nailed it with that post.  High capacity signalling (CBTC, ERTMS level 2 or higher, any other bespoke ATP & in-cab signalling system) will not, by itself, give significant additional capacity.  The physical infrastructure of the railway also has to be engineered to suit - layouts at junctions & stations, speed of turnouts where lines split for platforms, etc. The trains also have to be operationally suitable - rapid braking & acceleration to clear the short sections or advance the moving block, wide doors for rapid passenger movement so dwells are short.  Finally the culture & organisation of the railway itself has to support the style of operation planned.  Fail on any one of these things, and your billion dollar fancy signalling system just becomes a white elephant.  

As Mufreight points out as well, these kinds of system tend to lead to total system failure if anything fails.  There need to be fallbacks in place to allow degraded operation to continue if something breaks.  It only takes one failed train with the emergency brake jammed on by a recalcitrant computer, and the whole thing is stuffed!  Metro CBTC systems are therefore engineered to gracefully degrade through various operating modes from full ATO operation to some kind of degraded or fallback comms method (e.g. by sending speed codes via variable balises if the comms are down), all the way to isolation of the system and "driver responsible" operation to the lineside signals or even manually issued authorities.

For those reasons, very high throughput is usually only achieved on custom built metros which are designed from the outset for that kind of capacity.  Retrofitting to a general purpose railway like QR is a much more expensive & compromised business.

In the QLD context that means that Cross River Rail can be designed for high headway from the outset, whereas the legacy route through Central and South Brisbane will probably be much more difficult to make perform as well.

[#Metro]

You know, the original Wilbur Smith Plans 1970 wanted to build the Merivale Bridge to relieve capacity, and then build another bridge from Wooloongabba to CBD and then decomission the Merivale Bridge for "emergency use only". Instead Sir Joh built the Merivale Bridge along its dog leg alignment and that's what we got.

[BrizCommuter]

Some useful signalling links:
Metro signalling & Distance To Go
http://www.railway-technical.com/sigtxt2.shtml
ATP & Moving Block
http://www.railway-technical.com/sigtxt3.shtml
ATO & Multiple Home Signalling
http://www.railway-technical.com/sigtxt4.shtml
Route signalling
http://www.railway-technical.com/sigtxt5.shtml
ATC
http://www.railway-technical.com/sigtxt6.shtml
London Underground Signalling
http://www.trainweb.org/tubeprune/signalling.htm
SACEM (en francais)
http://www.metro-pole.net/expl/sacem/ch02.htm

[Zoiks]

ARTC  and its ATMS that it will be rolling out across its interstate network.
Could be cheap to implement in QLD when it is finished.

Only a short step into a proper moving block system too.

http://atms.artc.com.au/media/lockheedmartin.asp