So, with
@3973EXL's latest excellent updates, I thought I'd post up a "state of play" list of the progress so far. This post is for the "main" lines west of Didcot, through Swindon, and west to Thingley Jct & Cardiff; a separate post will be done for the B&H.
Didcot to Swindon - due to go live Easter 2018
Steventon excepted, all steelwork (including SPS) looks to be complete from Didcot to Swindon.
A note on Steventon: The railway over the Level Crossings & under the High St Bridge (aka the "Brunel Bridge") WILL
be electrified; however, the bridge may well be demolished in CP6.
Steventon-Uffington-Swindon
From MP55 3/4 to MP57 1/4, most masts up in various states of fitting out. At Steventon, all masts are up, with just a few last bits of SPS to go up west of the bridge.
Wires start after MP57 1/4 (400m west of Causeway Crossing), with a break on the Up line just east of Uffington X-overs.
West of Uffington, after MP67 1/2, the wires continue to approx MP72 1/4, with a small gap just east of Bourton X-overs.
West of Bourton the wires resume and continue, almost to Swindon: as far as Highworth Jct (76m 32ch) on the Down and as far as the western end of Swindon Dn Yard (76m 64ch) on the Up. The USGL at Stratton (Swindon Up Goods Loop) is also wired.
Swindon
All masts and portal booms are up, and SPS is starting to be installed; from east to west as far as the old Swindon B signal box. Only one cantilever boom/portal boom needs to be put up at the western end. Three bare tall masts (one at London end of P4, 2 at Bristol end of P4); presumably for power supply feed.
Swindon-Wootton Bassett
Rushey Platt (MP 78 1/2) has a single wire run from the UM onto the loop, while the Down line through it has 2 wire runs finishing further west.
The Up Line also has two wire runs, from MP79 to MP79 3/4 and from MP 81 3/4 to MP82 1/2.
Wootton Bassett's steelwork, mainly portals, isn't complete but still looking quite near complete.
The "Main Line"; Wootton Bassett Jct - Chippenham - Thingley Jct
Track lowering and drainage work at Dauntsey completed.
Nr Callow Hill, pretty much all the masts are up, TTCs, STCs and portals alike; most have SPS fitted now.
First few headspans (?) erected over 25/6th of Feb '17 at Dauntsey Bank (87m ish), and some (not all) of the missing masts have gone up too, plus brackets for fittings.
Masts up just east of Chippenham, in the Langley Burrell area; works compound established at Langley Green L.C.
Quite a few masts (some with cantilevers) now up between Chippenham & Swindon, going most of the way from there to west of Swindon stn (except for a small section where signal ducting needs replacing)
~60+ masts up, 35% piling complete between Thingley Jct and Royal Wootton Bassett.
South Wales Main Line (Wootton Bassett Jct-Bristol Parkway-Severn Tunnel-Newport-Cardiff)
Wootton Bassett - Bristol Parkway - Cardiff set to go live in April 2018; chance would be a fine thing!.
Wootton Bassett Jct to Bristol Parkway
Almost all piles in, and 70% of them have masts.
11 odd miles worth of wires up from Wootton Bassett (MP 83 1/2) to just west of (and including) Hullavington loops.
O/H Conductor rail installed in Chipping Sodbury Tunnel.
Progress as well around Chipping Sodbury/Old Sodbury; many masts up, some with booms attached, and SPS now appearing too.
From Westerleigh Jct to Bristol Parkway; fewer than 20 bases are mastless now. Most SPS is concentrated at the Westerleigh end. A run of masts (all boomed) has sprouted on the curve towards Cheltenham Spa.
The "Blue Viaduct" over the M4 just east of BPW now has SPS up on the masts along it.
BPW Platforms extensions underway; TTCs up over P1.
Bristol Parkway to Pilning
Patchway Tunnel conductor rail installed. Masts, booms and SPS up through Patchway.
At Pilning, piling and masts appearing towards both Cattybrook & Severn Tunnel, Platform 2 now closed. SPS going up on some portals too.
Stoke Gifford IEP Depot all wired.
Piles/mast bases between BPW and Cardiff look almost complete.
Approx. 70% masts now up between BPW and Severn Tunnel.
Severn Tunnel to Newport
Severn Tunnel Conductor rail in place .
All bridge rebuilding complete from Severn Tunnel West to Bishton Flyover.
No masts until 1 mile east of Llanwern, Masts going up between Bishton Flyover & Llanwern W Jct, and around Marshfield; approx. 97 from Ebbw Jct to Marshfield.
Maindee Jcts
Cluster of piles now in on the south side of the line.
Newport
Canopies cut back pending wires; being done in 30ft sections. Masts and portals now appearing at the western end of the station, some with SPS attached.
Some concrete bases in between stn & tunnels, perhaps for portals.
Old stn footbridge and another bridge further east gone.
Newport to Cardiff
Masts and portals appearing near Duffryn. Some with SPS.
Cardiff Central
Re-signalling completed. Platform 0 now open. Some masts now up over P0/1 with TTC booms.
Swansea IEP Depot
New IEP Depot at Maliphant Sidings, Swansea now complete; all steelwork up but no wires.
Do let me know if there's any changes I've missed!