Disruptions yesterday and Friday at Spencer and Flinders St respectively had me wondering how much operational flexibility will actually be present post-Metro Tunnel. For example, on Friday with platforms 8-13 out of action at Flinders St, a goodly number of Werribee trains were able to be routed via the Loop and the balance of Werribee/Williamstown services were booted off at North Melbourne to transfer to Loop services. I was actually very impressed with how Metrol handled the whole episode - minor delays to Sunbury/Craigieburn/Upfield were a sensible price to pay for keeping the vast number of Werribee/Williamstown pax moving.
Consider a similar scenario in 2026: a small fire at Town Hall in the middle of morning puts both platforms out of action until electrical services have been restored, which takes about 2 hours. The nearest western turnback for down trains is at Sunshine (correct me if I'm wrong but I don't think West Footscray will have facilities for turnback in that direction), meaning buses have to be arranged in a location with very poor road access and disastrously congested city access. It's carnage. On the other hand, if the main suburban lines are retained between South Kensington and North Melbourne - and the publicly released plans seem to disagree on whether this - then trains can be diverted to North Melbourne platform 3, allowing pax to transfer at Footscray or North Melbourne for city access with minimal disruption to Craigieburn and Upfield services. Another alternative is adding an emergency crossover on the up side of Footscray for the same reason.
The scenario is less grim in the east given the ability to terminate at Caulfield.