A different kind of rail query there. As someone who prides on being rather knowledgeable on the South Wales stuff, I'd like to help! What sort of things do you need to find out?
I would check my copy of The Down Fishguard DVD, but unfortunately it has been ruined beyond all repair. Which is extremely gutting. I can tell you the one by Landore, Swansea replaced the original Brunel-designed footbridge some decades ago, but I can't give a date yet.
I'll see what I can find out, but I can't promise anything just yet.
I do believe Loughor (pronounced something like Luck-or) Viaduct is a single-line bridge, which returns to double-track a little bit beyond the bridge.
Like I say, I'll try and get you some answers, but I'm not sure if I'll be able to find anything. Definately try Google for some ideas!
EDIT: Closest I've got to photos of the bridge to the west of the Carmarthen Triangle is a quick sight of it on my mini DV tape of 37419 tackling it on 14/12/05, but I don't know where that tape is either. I've been on the road by Loughor Viaduct, it's not a particularly fancy bridge IMO, mainly steel sides, a small fence, iron supports (I think) and a 20mph freight speed limit (I can't recall the passenger speed limit)
As for the SDL's viaduct, is that the one that passes by Junction 45 of the M4? That's not a particularly fancy bridge either. Been under and over it a good few times (more under than over), but never been able to get a photo. If I were still in Swansea, I'd go and get shots of all of the ones you want, but I'm too far away to go and do that now.
