Well, as a signaller with experience of 8 and 12-hour rosters, I much prefer the latter - to the extent that I don't think I could return to '8s' now.
It isn't just that a typical 8h roster at a single-manned 'box requires you to work more often; it's how those shifts are structured, with long runs of consecutive shifts during each 28-day cycle: seven successive earlies (including a 12-hour Sunday) and - the most fatiguing - working 13 days out of 14 on a lates/nights rotation (with the sole [twelfth] 'rest' day wasted reorienting your body clock after a week of nights). I look after myself, but I was always knackered by the end of both of those sequences.
'Twelves' are a breeze by comparison. Quieter, single-manned 'boxes have gaps between trains; and larger, more demanding (i.e. highly-graded) locations provide breaks. My place typically works two hours on, one hour off, so although my shifts are longer than an 8-hour roster, my time on duty isn't - and I get more days off. Noticeably less tiring, IMO - and that's before we get onto fuel savings etc.
I accept that people with longish commutes might initially be reluctant to move to, say, 14-hour working days, but several of my colleagues do just that and, to a man/woman, they would never go back to '8s'. I'd wager any straw poll of signallers who've worked both rosters would produce a similar result. An increasing number of 8h 'boxes are moving to '12s', but I've yet to hear of a single location lobbying for the reverse - that must say something.
Re historical norms, my part of the country has traditionally been dominated by 8-hour rosters (often containing worse shifts than those mentioned above - 'Doubling Back', anyone?). 12-hour rosters have only begun to creep in relatively recently, and are still the exception.
