Based on Japan using passing loops to ensure express and all-stop trains can run at 10min frequencies each all day on double-track corridors, what if the middle track of the Northgate-Petrie or Boggo Road-Kuraby corridors by used by the Redcliffe or Beenleigh trains to let the express SC or GC trains pass through at stations during off/counter-peak?.
For example, an off/counter-peak Redcliffe train could switch from the outer track to the middle before stopping at Sunshine to let the SC train pass by. Afterwards, the Redcliffe train can continue on its journey from Sunshine.
I am aware that there are no track switches around the stations on the 3-track corridors and that the 7min-frequent peak-hour trains occupy the middle line. So how much will it take to add a few switches at certain stations, as well as timetabling the services so that the counter-peak all-stop trains arrive at the station shortly after the the peak-hour train departs?