What happens when the Gawler line is electrified as far as the Dry Creek depot, to allow the electric units to travel there under their own power for servicing. Would that prevent Jumbos running on the Gawler line too, which would severely limit their use?
Once the overhead is installed & energized on the Gawler line towards Dry Creek, it will prevent Jumbos being used anywhere on the Adelaide rail system.
By the time this part of the electrification project happens, hopefully there will be enough new EMUs delivered to allow most/all Seaford & Tonsley trains to be electrically operated.
There will then be enough DEMUs to allow all Grange, Outer Harbor and Gawler trains to run with 3000-class units & all Jumbos will be retired.
In the short term, once the wires are energized on the Seaford & Belair lines through Adelaide Yard and into platforms 1 to 4, there will need to be some procedures in place to prevent a train formed of jumbos being accidentally signalled onto the south side of the yard (and under the wires) at Nairne Junction.
Especially at times of disruption when normal routes and platform allocations get modified on short notice.
As the signallers will not always know whether a train on their computer screen is 2000 or 3000-class, how will this be achieved? By relying on the driver remembering "I'm driving a Jumbo, I can't cross over there!", and stopping his train?
Since the rail authorities don't trust their drivers to stop at red signals, and implemented the "pass all yellows at 40kph" rule, I'm not sure they would take this risk.
Same thing applies to an EMU arriving off the South Suburban (Belair) line getting signalled into Platform 5 (non electrified). Will they rely on the driver remembering and not running out of wire? An opportunity for a new type of peak-hour debacle waiting to happen?