Recent discussion to revert to single deck trains on some of Cityrail’s lines as part of a metro proposal (discussed by me here, here and here) are somewhat ironic when you consider that Cityrail spent much of the 70s and 80s upgrading its fleet from single deck trains to double deck ones. The idea behind this was that it would allow Cityrail to increase capacity without increasing the number of carriages per train. The limitation was a number of stations (particularly in the CBD) which were either too short or too difficult to extend. To borrow a saying from urban planning, if you can’t build out, then build up!
The first double deck trains were the Tulloch trailers, introduced in 1964. However, it was not until the roll-out of the L, R and S Sets during the period 1972-80 that a significant portion of the rolling stock was converted to double deck. LRS trains are the steel trains that today form the backbone of the Cityrail network. They were functionally identical, and designated L, R or S based on the number of carriages that they had (3, 6 and 4 respectively). Later in the 1980s came the C and K Sets, which again were the steel trains, with the major difference that they had air conditioning. All LRS Set trains are set to be withdrawn once enough Waratah trains are delivered to replace them (all 78 are currently scheduled to be in operation by 2014), resulting in a fully air-conditioned fleet.
Despite all this, the Cityrail fleet was not actually fully converted to double deck rolling stock until the introduction of Tangaras, which were rolled out between 1988 and 1996. Towards the end of this period, in 1993, the last of the single deck trains, the Red Rattlers, were pulled from service. I rode on a Red Rattler only once in my life, immediately after arriving in Australia in 1989. Ironically, it broke down, requiring us to change train. I didn’t miss them.
The interurban fleet saw a similar conversion, with single deck U Sets being replaced progressively between 1970 and 1996 by double deck V Sets (and also briefly by Tangaras, before the introduction of the OSCAR allowed all Tangaras to operate exclusively in the suburban network, rather than split between suburban and interurban). Diesel trains, operating in the Hunter, Southern Highlands (both by Cityrail) and further out (by CountryLink) remain single deck.