There is also the possibility of new stations being built east of Newport - a parkway station near Llanwern, and perhaps one to serve a more local population at Magor.  With the cancellation of the M4 relief road around Newport, I can see greater use of the railway to take the pressure off the M4 for local journeys becoming a priority for the WAG^» (Welsh Assembly Government - about).  Ideally there would also be an all stations from Cardiff to Bristol Parkway, giving connections into Inter City services there.  Despite being on the main line, Severn Tunnel Junction has no direct services that go to Bristol Parkway, let alone London (except on the days when the 0730 Cardiff to Portsmouth is short-formed!)

Yes - I realise the rest are still in the queue at Wabtec.  The point I was making is that GW05 and GW06 have arrived since the May timetable started, but I'm not aware of any new Castle diagrams.

Running a 'right time' railway is, of course, crucial to running a reliable railway.  With trains and crews used so intensively, turnbacks short of the final destination and skipping stops means cancellations for the customers affected.

As well as having the necessary resources available - trains, track and staff - the timetable needs to be designed as far as possible so that a 5 minute delay on one service doesn't delay several others, causing trains to lose their paths elsewhere, and spiralling knock-on effects.  Since Network Rail determine the fine detail of the timetable and make signalling decisions, I think they are ultimately the ones who must answer to this.

A good example of a line where delays quickly multiply is Bristol to Taunton due to the mix of fast and stopping services and single-track Weston Loop and junctions either end.  Often it is a late-running westbound Cross-country service to that starts the rot.  It passes Uphill Junction late, so a Cardiff - Taunton can't come off the Weston Loop, so the next Taunton - Cardiff is held on the main line because it can't go onto the Weston Loop, and possibly a fast service then gets stuck behind that.  And then the delayed Cardiff - Taunton has a short turnaround time and is consequently late coming back.

What can GWR^▸ (Great Western Railway) do to avoid situations like this, when the factors are largely outside their control?  XC^▸ (Cross Country Trains (franchise)) not running on time, insufficient pathing margin in the timetable, and a restrictive track layout at Uphill Junction?  It would be good to see CP6^▸ (Control Period 6 - The five year period between 2019 and 2024) used to improve resilience at points in the network where conflicts like this frequently arise.  Bristol East is another.  I think it's less about adding extra tracks but allowing untangling the paths that cross with each other.

Also the connections from Bristol to the Hereford line at Newport, which, as I mentioned recently, are broken in the new timetable.  There are an increasing number of commuters from the Cwmbran / Pontypool area who work in Bristol - houses in a number of new developments are being snapped up by people who work the other side of the bridge where the house prices are rather higher.

Back in the 1980s there was talk of running Hereford to London trains via the Marches Line - rather quicker than the alternative route via the Cotswold Line - but that never came to fruition.  I've often wondered whether an Abergavenny to Bristol Temple Meads service could tap into this commuter market, though I'm not sure whether either TfW or GWR^▸ (Great Western Railway) would be be interested in running it.  Perhaps one for an open access operator?

I notice the 1200 and 1800 ex Cardiff; 0916 and 1456 ex Taunton diagram has been a 'classic' this week.
That's classics on most of this route's diagrams now, isn't it?  Exceptions are the 0602 TAU^» (Taunton - next trains) - CDF^» (Cardiff - next trains) / 0900 CDF - PLY^» (Plymouth - next trains) and 0925 SJP - CDF / 1300 CDF - EXD^» (Exeter St Davids - next trains), I think.

I understand that GWR^▸ (Great Western Railway) now have 6 'castles' - they're not all required for the far west services, so where are the others?  I haven't seen any on the Cardiff to Taunton run since the May timetable change.

There is also the question of why a whole class of emus seemed to have a problem re-starting after the power came back on again.  Fitting trains with a backup battery or diesel engine might not help if they shut down and need a technician to come a couple of hours later to persuade them to work again.  I think there was a suggestion that it was the drop in AC frequency that tripped the trains' systems out?

National Grid were saying that they need to consider carefully about what to disconnect to minimise disruption - but when a main railway line presents such a variable and asymmetric load on the grid, is it not one of the first they would choose to shed when trying to stabilise the supply?

Surely that would be the end of being able to take advantage of split ticketing?  And not knowing how much a journey actually cost you until you see your bank statement sometime later??  In urban areas with zonal fare structures it could work well, but until the thousands of fare anomalies are fixes across the wider rail network I fear a lot of people would feel they were getting ripped off by such a system.

I was at what I think was maybe the last Meet the Manager session, in Cardiff in April last year.  My recollection of that one was that it was very well attended, and a worthwhile evening for customers and GWR^▸ (Great Western Railway) alike.  Main problem on that occasion was that there was not enough time for discussions to be properly concluded.  Certainly people weren't rushing away to get home - but maybe you get a different sort of audience in Cardiff than, say, Paddington where there will be more hard-pressed commuters who have just finished a day's work and still have a long journey home.

Another downside of the new timetable is that the acceleration of the PAD^» (Paddington (London) - next trains) - CDF^» (Cardiff - next trains)/SWA^» (Swansea - next trains) services means that many BRI^» (Bristol Temple Meads - next trains) - CDF services need to be re-timed to run after them rather than before them, worsening connections with the Hereford line at Newport.

According to RTT^» (Real Time Trains - website), early evening 'connections' at Newport will look like this:
arr from BRI: 1701, 1730, 1804, 1831, 1910
dep to HFD^» (Hereford - next trains): 1701, 1731, 1803, 1835, 1909

Until there is a re-cast of the Marches Line timetable, I guess there's not much scope to fix this.

A few more quick calculations.  Contact wire has cross-section of 120 mm2, copper has resistivity 1.7 x 10-8 so 1.4 mOhm per metre.
If a train is drawing 10000 kW at 25kV, that's a current of 400 A, which would cause heating of 23 W per metre.

Heat capacity will be about 400 J per K per m, so rate of heating would be roughly 1 degree every 20 seconds.

Of course, I've ignored the heat generated at the point the pantograph touches the contact wire.  I've no idea how to estimate that, though any heating effect must surely affect the pantograph more than the wire.  Do pantographs get hot?

Wires now up on all lines through Newport, except missing the contact wire on the down main across the river bridge and through platform 3.  Quite a productive weekend possession, it would seem.

More of a breeze a few metres above the ground, and not much effect of heat radiated from the ground - I reckon the wires would be significantly cooler than the rails on a sunny day.  Could try using chrome plating the wire to keep it even cooler?

Thanks for all the technical details to satisfy my curiosity - all very interesting!

I did a quick calculation.  A 1000 metre solid copper cable would extend by 85cm if heated from -10 to +40 degC.  OK, so catenary is made of twisted strands, and is some sort of alloy, but I guess the extension would be of that order.  But then, the catenary is clamped at regular intervals - surely it must be able to slide through these to allow for expansion and contraction?

I also wondered whether the catenary and contact wire will stretch a bit over their lifetime - they're under considerable tension, after all.  Do the tensioners and weights need adjustment from time to time, and could that be part of the problem if they hit their end stops in very hot weather?   

Of course, you'd still need to go at least as far as Patchway to make the return journey.

Finally opened today - though the lifts are not yet in use.