Presumably, her four double deck NWRL trains alternative would be displacing the present four through Pennant Hills, which would instead travel via Strathfield, as the Chatswood-CBD section is already at its 18 trains per hour (including the present 14 per hour for the North Shore/Central Coast) capacity under present operating conditions that prevent a possible 20 trains per hour being achieved. These conditions include key flat junctions west of the CBD, many passengers transferring to/from other lines in the CBD and passengers waiting on crowded narrow platforms for a particular train.
Clearly four double deck trains for the NWRL would not be enough, and an extra four (or more) could be provided to Chatswood to meet the demand and provide more seats than 12 single deck trains. However this would then more heavily load other services south of Chatswood such that the reliable headway might fall to around 16 trains per hour and crowding reach barely tolerable crush conditions. The fix, as with the single deck solution, would be to terminate all eight double deck NWRL trains at Chatswood and separately alleviate the operating constraints between Chatswood and the CBD. Although terminating all eight double deck NWRL trains at Chatswood could allow four trains per hour to travel from the CBD to Hornsby via Chatswood and Epping, this would add to the problematic operating constraints and thus be counter-productive.
Timetable changes west of the CBD can eliminate key flat junctions, and also, in conjunction with running all trains between the CBD and Chatswood on one route only (to Lindfield and beyond), reduce the waiting on crowded platforms for a particular train (because more passengers take the first available train). This constraint easing maximises the probably that the full 20 trains per hour capacity, and possibly a little more, can be achieved.
In summary, for peak periods before a second harbour crossing, it appears necessary to terminate all NWRL trains at Chatswood and also not allow a direct Pennant Hills-Chatswood service to be provided, noting that the option of running some NWRL trains via Strathfield instead has been lost with the wholly underground connection to Epping. Accordingly the true comparison would be between 12 (or more) single deck NWRL trains per hour (faster and more frequent) or eight (or more) double deck trains (more seats). In off peak periods and at weekends, direct Pennant Hills-Chatswood services could be provided under the double deck alternative only, however some of the services (out of NWRL, Hornsby via Epping and Hornsby via Gordon) would need to terminate at Chatswood to avoid exceeding capacity between Chatswood and the CBD/West.
In the longer term, after a second crossing, the total capacity constraint south of Chatswood would be eliminated and 20 double deck trains per hour over the bridge should be possible if most of the transfers to/from other lines are absorbed by the second crossing, even if multiple destinations are restored. This second crossing could be single deck only, or also for double deck, with significant engineering benefits (grade and line capacity) for the former. The subsequent discussion assumes single deck only (a personal view) but it does not affect the capacity implications. It is then logical to allocate single deck trains to the most appropriate route, and that is the all stations short haul to Gordon on segregated (from double deck services) tracks. This would entail a single deck dive connection from Waverton to Victoria Cross (North Sydney) and to the second crossing tunnel, and a St Leonards to North Sydney tunnel via Crows Nest for double deck trains. As well as additional tracks between St Leonards and Gordon, new single deck underground platforms would be needed at Chatswood to preserve the existing surface turn back facilities for trains not proceeding to the CBD.
Making all to Gordon segregated single deck would eliminate four double deck Gordon terminators per hour and allow a reduction of two Hornsby via Gordon services during peak periods, leaving a requirement for eight upper North Shore/Central Coast services per hour as double deck. The remaining 12 double deck trains per hour via Epping to the CBD would then be split between NWRL and Pennant Hills services, and additional services could also be introduced provided they terminate at Chatswood (alternatively, some Central Coast services could be terminated to allow others to travel through). Shuttles to Parramatta could also be terminated at Chatswood within the present safety constraint of 20 trains per hour on the Epping-Chatswood sector.
The end result would be the longer term use of double deck trains for longer routes with greater average station spacing where seats are more important than dwell time/frequency, and single deck trains for shorter routes where the reverse is true. The underused cross harbour single deck capacity has potential application for a future Brookvale service. Although the single deck solution has some specific short term advantages for the NWRL during peak periods, these will be diluted in the longer term with through working to the CBD, and accordingly any such single deck rolling stock initially used on the NWRL should be redeployed to other routes where dwell time/frequency, and potentially line capacity, is more important than seats.
12 May 2013