There is no doubt that a new harbor crossing needs to be constructed starting right after the NWRL, with all planning done and ready to go at that time.
There are currently 15tph in the peak hour from the north that are not ECRL services, including 3 from the Central Coast.
In the short term, the North Shore line could handle the load with some changes - I think this is what would need to be done to make it comfortable:
- Upgrade signaling to 24 TPH - if we are running 12tph on the NWRL this allows consistent patterns to be observed at Chatswood
- Extend quad to St Leonards to allow extension to NWRL services which will both reduce the number of people needing to change (those who work in St Leonards from the NW) as well as freeing up more space on shore service for those who do need to interchange (those who work in St Leonards from the North Shore)
- Repeated 10 minute service pattern in this order:
- 6TPH Berowra starters
- 6TPH Gordon starters
- 6TPH Hornsby starters
- 6TPH Lindfield starters
- NWRL service timed to arrive just after Hornsby and Berowra starters, before the shorter starting services to ensure less crowded services for interchange
- Consider removing more seats from vestibules to improve circulation in door area, replacing with perch seats - leave 2 sets of 2 seats per vestibule for priority seats
There shouldn't be publicised timetable if possible, rather just service intervals. The above should work most of the time but if connections are missed things should recover quickly.
Central coast services would have to head via Northern Line, however in the short term if it was desirable and there was capacity some of the Berowra starters could be extended - these would need to be all stops from Berowra though if you wanted to keep a 10 minute service gap, or could maybe skip to Hornsby if you were happy with 20 minute service gap north of there. The all stops nature could reduce these service's popularity.
An alternate approach is "demand management". Charge an extra $2 per trip for NWRL PAX bound for the city who interchange at Chatswood rather than Epping.
Looking over http://farm9.staticflickr.com/8459/8069774920_0b4fefe14b_b.jpg
I've run a few numbers ...
Assuming the peak hour is half the total 3.5 hr AM peak loading (roughly right), here is an analysis of the bussiest line: Sector 3 East/North bound: platforms 16 at Central, 3 at Town Hall, 4 at Wynyard
Total transfers *to* Sector 3 in the AM peak are:
From East Hills: 1500
From Bankstown: 1500 (though these could easily take place at TH)
From South: 3000
From Inner West: 3000
Interurbans: 1500 (Bound for the North Shore, others are assumed to use sector 2)
Total: ~10000 or 5000/hr in the peak hr.
From Illawarra: 3500
From Eastern Suburbs: 1500
Total: ~5000 or 2500/hr
Alightments in the CBD (assumed to be 25/37.5/37.5 split over Central, Town hall & Wynyard) from Sector 3:
(Adjustment because some northern PAX travel via the Nth Shore and/or ECL) -3000
Total: ~32000 or 16000 in the peak hour. By the split assumptions, I get:
Boardings in the Peak hr:
Central 16: 4000
TH 3: 6000
Central 16: 5000 on, 4000 off: ~450 movements/train.
TH 3: 2500 On, 6000 Off: ~425 movement/train.
So we're looking at ~400-500 movements per train, which is (on average) 25-35 movements per door, and these give rise to dwells of 50-60 seconds. Obstructed channels have a bit to do with this, but the dwell is determined by the slowest door, and a fast dwell is really only achievable if all 16 doors are unobstructed.
What's going to happen at Chatswood post the NWRL? At 8000 PAX/hr - the probable initial peak patronage - it seems withing the interchange capacity achieved at the other busy stations. But ... this won't be spread over all DD trains through Chatswood, it's going to fall unevenly on half of them in the AM peak.
That means you're already looking at 650-700 boardings after each NWRL train arrives. Perhaps, with near empty trains and thus unobstructed doors then this can be done in a 60 second window. At 10 000 PAX/hr - probable NWRL patronage by 2022 - we're looking at >800 movements per train: double what takes 60 seconds to achieve in the city.
If that is attempted with full or even partially loaded trains, dwell times are going to blow out into the 70-90 second range. To achieve 24tph in that environment that means a 60 second signal headway. That is not completely impossible (with a
What I really disagree with Grog on is the recovery. I think a single delay of more than 90 seconds anywhere on the DD network will see the SD and DD interchanges run out of phase. That just won't recover until the DD timetable is delayed by a quantum of 2 slots to restore the empty/full phasing of the trains to match the NWRL. And even then, you'll end up trying to load 1600 PAX from 2 NWRL trains onto a single DD train (which would probably take >2min) throwing the systems out of phase again. So I think this interchange would be completely intollerant of any delay.
In my view, the Chatswood interchange is going to set the capacity limit of the NSL, probably at about 10-15% below the line's capacity, and possibly even it's current capacity even with 24 trains an hour.
The Olympic Station achieved >20kpax/hr boarding rate, though it did this with completely empty trains and bifurcated platforms.
It should be noted that while interchanges are common on most networks around the world: more common than on CityRail, very very few dump an entire metro line onto an S-Bahn type service. They are usually spread out over multiple stations or multiple lines.
There many and varied engineering solution to this problem. A(nother) turnback at Chatswood to ensure completely empty trains meet the NWRL trains is one. The second harbour crossing is another. Quadding to St Leonards to try and spread the interchange load. And extra up platform at Chatswood for the NWRL. Run the NSL using faster boarding SD stock.
But the most blindly obvious solution to not require the interchange at all and to run the entire NSL using the same format as the NWRL, and I think it's all but inevitable this will end up happening.