Mr ParnellThanks for your reply Ian,
As you observed the old time table had about 4 trains per hour. The 13 minute time interval could only occur if a movement started from Belair rather than be formed from a return movement.
This can be achieved if trains are stabled at Belair AND can also be achieved if a down train consists of enough cars to make up two return up movements.
For this to work a down train from Adelaide comprises tow trains which split on arrival at Belair. The first portion departs as the first up train
The second train leaves 13 minutes after the previous train which allows the next down train 17 minutes to come from Blackwood, split if necessary and form the next up movement or movements.
Likewise in the evening, two down movements could combine at Belair to form a single up movement to return the cars to Adelaide and Dry Creek RC Depot. No additional cars or crews are required over the number required for the services starting/terminating at Blackwood
With cars for the Belair service having to make the empty runs to Dry Creek to fuel up, overnight storage at Belair may no longer be practical. Formerly the cars which stabled at Belair could be serviced and fuelled at the Adelaide RC Depot during the day, now it requires a run out to Dry Creek with has to be slotted into the Gawler line timetable.
The 15 minute intervals is consistent with the proposed services to Seaford and Tonsley, also 15 minute intervals. Keeping the Belair line trains in synchronism with this allows better use of the infrastructure. The 13 minute interval for departures from Belair would work if these trains waited at Blackwood for 2 minutes such that from Blackwood they followed the previous train by 15 minutes. The 13 minute interval may in practice have to be 12 minutes with a 3 minute hold at Blackwood.
The problem with your survey is that people will almost always want more than they have. I suggest you should also conduct the survey at Blackwood to see how many people, if any, drive from Belair.
I'm on a steep learning curve in relation to the intricacies of timetabling, but what you've said makes sense. I approach this exercise from a consumer's perspective and then leave it to the technical people to work out what is possible. I want more public transport, not less. There's often a big difference between what is possible technically and what they are prepared to do politically.
It seems to me that the heart of the problem is the closure of Belair depot and their reluctance to stable or fuel trains there. Thinking ahead to when the whole network is electrified except Belair, it seems that there will need to be dedicated infrastructure including a dedicated platform at Adelaide, so I think a case could be made for re-opening Belair. I'll be raising this with the Dept.
One of the questions I asked people from Belair / Pinera / Glenalta is whether they are likely to drive to Blackwood. I know some will, but the test will be in the carparks. Also, plenty of people raised the spectre of the last 3 stations closing - perhaps that's another good reason to agitate for the depot to re-open?