Who knows, if an updated version of the A-City is selected for the next order of 15 units (to serve the Gawler line) they might have them numbered as 41xx to denote the updated versions as opposed to those which were delivered and later had the updates (e.g. stronger floors, directed horns, quieter air conditioning) retro-fittedIt would be interesting if a later series of A-City railcars has a fourth segment. How it would be done is another question. The current setup distributes the mass fairly evenly between the three segments and as a result a fairly controlled handling. If an unpowered trailer of different mass were added this can cause strange oscillations and limit speed. If a powered car was added the trailer car would maybe need heavier power supply items and upset the balance as well.
That would be quite easily sorted out. For all the problems with the A-City design that made for such a lengthy gestation, they have been well-specified in terms of allowing for future expansion.
Remember that the A-City is basically an Electrostar with a different body shell, and Bombardier have managed to make Electrostar EMUs in 3/4/5/6 configurations over the years without any problems. They've also handled post-sale addition of extra cars into sets as well, in case that becomes a possibility here.
The A-City design does have the advantage of the unit having bar couplings, which brings handling closer to that of a single vehicle than a train with couplers between each carriage.
Were fourth cars to be ordered, they would be either a ballasted trailer or a motor car. If a motor car were to be inserted into the formations, the control software would be reconfigured to change the governing of each car's motors. Happily, the theoretical maximum power of 1.6MW on the A-City is quite sufficient for a four car version (the performance is already heavily governed) and there wouldn't need to be any changes to the supply kit..
If a ballasted trailer were to be picked, the 'ballast' should actually be a battery pack which would allow the trains to:
- drive to the next available station in the event the wind dies down and a cloud floats over at the same time, and
- cover short single-track sections like Gawler-Gawler Central, Gawler-Roseworthy, Alberton to Port Dock and Woodville-Grange without needing overhead wiring, and
- allow the Belair line to be upgraded to discontinuous electrification and battery power to be used through the tunnels.
It's something that will have to be addressed at some point, since nobody will be making DMUs any more when our current DEMU fleet finally reaches life expiry.
Bombardier do have some experience in this area, they have been working on a prototype B-EMU using a Class 379 Electrostar unit in the UK. That's a further good result for us from selecting an Electrostar with an Australian-spec body shell.
A few years ago a hybrid/mixed power sourced train came unstuck in Spain. I can't help but think that the unbalanced nature of the railcar had something to do with it.
A Talgo high speed set is basically a loco-hauled train with very lightweight coaches, not an EMU with a combination of motor cars and trailers.
The derailment happened because the train went around a sharp curve at over twice the speed limit thanks to the driver (since charged with 79 counts of homicide) being on the phone and reading a map instead of keeping an eye on the route ahead. A normal EMU would have handled that crash far more safely.
The issue there (and with the recent Amtrak Cascades derailment) is more about the safety of the Talgo coaches, in both incidents there were cars that were literally ripped open and people ejected. I would not ride a Talgo train if you paid me to.