Great Western Coffee Shop

From the Wiltshire Times (https://www.wiltshiretimes.co.uk/news/18293127.railway-bridge-collapses-train-goes-near-melksham/)

I took a stroll up to Dunch Lane where a vehicle hit the over bridge 9 days ago, and a train then hit the debris on the track.

One of the bridge pillars is missing:
(http://www.wellho.net/pix/dunch_20200318_01.jpg)

and if you look over the bridge, you can see all the old stone including the pillar top where it has been moved off the track:
(http://www.wellho.net/pix/dunch_20200318_02.jpg)

Dunch Lane is a very old lane over the railway which rises and falls sharply to the single track bridge, and it's become a bit of a rat run.  Age is seen in some of the very old fencing posts - broad gauge rails:
(http://www.wellho.net/pix/dunch_20200318_03.jpg)

And here's the Swindon train approaching:
(http://www.wellho.net/pix/dunch_20200318_04.jpg)

Headed away from the camera towards Swindon.  Note the irony of the diesel powered train going right past the Melksham Electicity SubStation - a rather large distribution point which would have enough "umph" in it to run a main line from Swindon to Bristol, with a side shoot all the the from Thingley to Taunton.:
(http://www.wellho.net/pix/dunch_20200318_05.jpg)

Why "would"? It's wired up and doing more or less that. OK, some of the wires haven't appeared yet, and Taunton is a bit further than they did in plan A, all of which is a little bit wouldy, but still ...

It's electrified ... thus far ... Swindon to Cockelbury Lane, on the outskirts of Chippenham which is a locations that's operationally in the middle of no-where. So every train that uses what's been done needs a secondary motive power - be it on board fossil fuel, stored electricity, or something else.

I'm unclear as to whether the feed does come up from Melksham or not to that point.  A lot of work was done burying a puppy [correction - supply  ;D] cable from Melksham to the railway at Thingley and I understand that a cable was to be run along the track through the station and to the end of the overheads.  I don't know if that has been done or not - it it has, a very different scale of engineering to the cross country section from Melksham Substation to Thingley Junction - as different as a 12" water main to a pipe to a domestic shower would be!

My "would" comment related to running train on electricity from Cockelbury Lane through Chippenham, Corsham, Box Tunnel, Bath, Saltford and Keynsham to Bristol.  Also from Thingley, past the source of power at Melksham to Trowbridge, Westbury, Frome, Castle Cary and Taunton.

Indeed - and it's unclearer than I thought it was. We know there's a National Grid feed at 25/0/25 kV from Melksham GSP to NG's terminating sibstation next door to Thingley ATFS. I've got documents for that, and the scar for the cable is visible on satellite pictures. There's also a shiny new white cable conduit from there along the track towards Chippenham. Unfortunately, from there to Royal Wootton Bassett Junction there's no pictures on Google Earth new enough and clear enough to show anything much. (And I still suspect that GE's offer of pictures changes with time for no obvious reason.)

There was to be an ATFS at Royal Wootton Bassett Junction, too, but it's not listed by NG as being fed by them. I found a newer picture for there (undated), which shows what could be an ATFS but no next-door NG substation, suggesting it cannot have a grid feed. Then I found report (a case study) by BCM Construction (but with NR's logo on it too) saying they have installed an independent feeder cable to feed Thingley Junction ATFS from Royal Wootton Bassett ATFS which has a grid supply. I can only assume that report was company PR and too little care has been taken over whether it's right about the feed direction.

There is a new conduit all the way - visible on the newer images - put in before most of the OLE supports went up, which suggests the feeder does run all the way too. The cable went in in 2016, probably before people were looking for such things, using NR Southern's cable train - though the trench under P1 at Chippenham people did notice. The cable is described as 2x1 core 630 sq mm, which I think could carry roughly 800A and so feed 40 MW; that sounds a bit low for a full ATFS demand.

So, while it's all very confusing, it does look as if power from Melksham feeds in only at RWB ATFS to supply down to short of Chippenham, and an unknown extent along the main line each way. At least, if all those ifs are true!

Out of curiosity, how can you tell that these are broad gauge rails? To my inexpert eye they're clearly a different shape from modern rails but I didn't even realise that broad gauge had a special rail shape; thought it was just the gauge. Couldn't they have been standard gauge rails (if they had been set horizontally at the required gauge rather than vertically in a fence, etc)? Perhaps Brunel used a special wheel shape?
Intrigued now...

They are bridge rails from the broad gauge era. They were laid along baulks of timber to form the line. The gauge was kept by iron bars between the two lines.
As time went by more and more track was converted to cross sleepers.
There were other broad gauge rails. Barlow Rail shown in the picture which had curved flanges. It was often used in sidings, as at Weymouth. The picture show its later use as gateposts at Chippenham. Then there was MacDonnel plates which were used on the Bridport branch. These were laid on the the ballast and the lighter weight bridge rails lay on top. Again metal ties held the gauge. The one in the photo comes from Brian Jackson’s Bridport Branch (first edition)


https://didcotrailwaycentre.org.uk/article.php/20/broad-gauge-railway

http://www.railalbum.co.uk/early-railways/brunel-gwr-broad-gauge.htm