Increasing train length is most cost effective capacity solution

The CBD & Southeast Sydney light rail line will have the world's longest vehicles at 67m.

For heavy rail, 10 car trains were revealed in internal Transport NSW documents as one of the most cost effective measures for increasing capacity - a 25% capacity increment for only $149m for Western line station lengthening, and $149m for Richmond line station lengthening:

Compared to the billion dollar costs of track amplication, or signalling upgrades, or single deck metro conversion, increasing station length at $298m is amazingly cost effective.  Of course, additional rolling stock is an extra cost, but extra rolling stock would have been required for other capacity upgrades.

It seems Infrastructure NSW have caught onto this.  Instead of going for 10 car trains on the western line, their 2014 State Infrastructure Strategy Update gives a business case 12 car trains - a 50% capacity increment!