Usually I'm the first in to drag GWR but I have held back a bit to look at things from both sides.
I am a commuter, and have been commuting only 20 minutes each way (inevitably it usually ends up longer) to Bath Spa. I can't give a straight answer if GWR have declined or not, without subdividing their network into different areas and stock. Firstly, as posted above, they seem to have got Cornwall and Devon right. Well, maybe except the Devon Metro, but generally they seem fairly popular in the far SW. I'm wondering if this was because Wessex Trains were so awful, that GWR look golden in comparison - or perhaps Wessex Trains already set the model and GWR didn't have a lot of work left to do? I'm not sure. I don't know the area well enough. I know that there is a lot of leisure travel in Cornwall so they are currently doing something right. I think GWR idolises Devon/Cornwall, and this can be seen in their advertising and general attitude. I'd imagine the Cornish mainline (at least) can be a fairly lucrative market due to seasonal traffic and long distance travel. There are also three train depots (Exeter; Laira; Long Rock) and 4 staff depots (Exeter, Plymouth, Par, Penzance) so if something goes wrong with staffing or traction, I'd imagine it would be less hassle to find cover compared to other areas of the network. Also many of the branch lines are self-contained throughout the day, removing the need for complex diagrams or junctions where other trains may cross. Although I don't know, I'm not sure if commuting is as intensive compared to other areas. A lot of the local Plymouth stations receive a poor service. Saltash, St Germans, St Budeaux, Dockyard, Devonport, Bere Ferres, Bere Alston, Calstock, Gunnislake and Ivybridge receive an average of 1 train per two hours. It's virtually impossible to use the Newquay line to commute. The Looe Valley line sees its service end early. St Erth isn't a big settlement as a terminus of the St Ives line. I'd argue that bus services in Cornwall get the brunt of the commuting, except maybe Falmouth - Truro which has received infrastructure improvements, allowing for 2tph. I wouldn't say it was "easy" to run Cornwall but it is probably the least foreseeably problematic part of their network.I travelled around Cornwall for three days last week and nothing was significantly delayed, though a 153 broke down on the Looe branch with road transport being provided the rest of the day. The Devon Metro is overwhelmed at peak time, especially as trains are regularly short formed here too with 143s being split to cover other failed trains or 150s/153s that have had to cover services elsewhere.
Next, South Wales - more specifically Swansea to Cardiff which is 1tph for most of the day with intercity stock with (usually) a generous turnaround at Swansea. Due to the current issues with the ATW franchise, GWR would naturally be the preferred choice here. Well, maybe up until a year ago as GWR intercity has become a bit of a laughing stock now (especially at weekends) due to crew shortage and cancelled services. Nevertheless, GWR seems relatively popular between these areas.
Cardiff Central is where things start going a bit wrong. The regional/local services to Portsmouth/Taunton start here (or are supposed to) but regularly don't due to train faults/broken down trains/unavailable train crew members/ signalling problems/ safety checks being made (delete as appropriate) which, granted, are not all down to GWR. All passengers see is 'GWR' on the side of the train, and 'GWR Service' on the station boards, so it is GWR's name that is usually at the front of the upheaval. The problem is with trains due to start from such a big station with long distance travellers, if it starts short (i.e. Newport or Bristol), many passengers are inconvenienced and will have to wait another half an hour at best and an hour at worst. In theory, 45 minutes should be enough time to turn around a train from Portsmouth/Taunton but regularly isn't, which suggests there are bigger issues elsewhere. Yes, you could board another train and change at Bristol Parkway but would that be quicker? Especially if a connecting XC train is delayed as they often are.
The Bristol area is a bit of a nightmare and I would argue a catalyst for a lot of the issues that happen on the GWR network. I'm not sure why but I guess is that it is many smaller multiple failings between GWR and Network Rail. There are a lot of long distance services that pass through the station on intercity and regional routes. The quad-tracking towards Filton will definitely help but I'd argue this should have happened years ago - I think there are too many trains that are currently using the lines through Lawrence Hill. 2 XC per hour, 2 Cardiff per hour, 1 Bristol Parkway local per hour, 1 Gloucester per hour, 3tp2h to Severn Beach and now one express to Paddington per hour. Any minor delay will cause a backlog, and with the Severn Beach trains being likely to be held at a junction before and a tight turnaround both ends with single line in between, it seems difficult to make up time as even if you do terminate the train short, it would normally have to wait for the next train to pass anyway. Bristol Temple Meads is also the land of the musical platforms. Once, my train changed platforms about 5 times, and ultimately ended up omitting my stop due to late running. Exasperating.
Bath Spa doesn't help congestion, due to the nature of just two lines through the station with a mixture of trains using them. Congestion at Bathampton is common, especially in the morning as if the "local" trains are running more than a few minutes late, they will be held for the Bristol fasts to go in front. Take my train this morning for example - it left my local station 9 minutes late, then arrived into Bristol 18 mins late and then ran through to Bristol Parkway omitting Lawrence Hill, Stapleton and Filton. My train home was about 15 mins late - And this is completely normal. The trains bound for Gloucester usually have very tight turnaround times of less than 10 minutes so any kind of delay will see them set off again late, cause congestion all the way to Bathampton and then cause disruption on the single line track to Weymouth, in turn delaying the next northbound working waiting at a passing loop. Realistically, the only thing GWR can do to keep to time is skip Filton, Stapleton Rd and Lawrence Hill, and then skip Bradford and Trowbridge - The latter two having plenty of long suffering commuters and are also two of the busier stations. Cam and Dursley, Yate, Keynsham, Oldfield Park, Freshford and Avoncliff only get 1tph and skipping isn't really an option after Westbury as all stations to Weymouth get an average of 1tp2h. There's also not a lot of recovery time en route for GWR Portsmouth trains.
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Next, the stock.
Firstly, it's great that GWR has passed over the 150/1s as those were not popular with either leisure travellers or commuters. So kudos for that. Next, the Turbos to Bristol. From a capacity point of view, things seem to have improved during 'normal service' (aka not disruption) so that's good as well. The stand out overcrowding in the area is now definitely the 158s on the Portsmouth services. Despite now having 'more stock', short forms seem more common than before on this route. My train to and from work are booked to be 158 (3 car) + 150. The 150 never seems to turn up on any of them which results in the 158 being completely overwhelmed with people not being able to board from my station onwards. Oh, it's fine, as the next service is booked a Turbo - Except that is running 20 minutes late and today it's a 2-car 158 that's jam packed. The reliability of Turbos seems a little questionable but I guess part of that is the crew getting used to them. GWR has paraded them for years now as solving all of life's problems... But they haven't, and won't. Internally, many seem in rough/ropey condition and generally feel very run down and uncared for. Some of the carpets are so threadbare, they are actually in worse condition than the 158s which are due a refurb, and that's saying something! Now the bulk of the 150s have moved away, we're left with 158s and 166s, both with extremely unreliable aircon and windows that don't open unless you can track down a member of staff which isn't possible if the train is crushloaded. The 3+2 seats haven't been popular with commuters and the WiFi is not reliable.
GWR knew that the Turbos would be moving to the Bristol area some time ago. How have local door controls still not been fitted to all units? Granted, better to run the train than cancelling trains throughout but it's still not really acceptable in my opinion. There are other Turbos fitted with them, can these not be concentrated on routes to Weymouth/Warminster that stop at the local door stations? Can there be another procedure put into place, similar to what happens at Melksham and Stonehouse in the short term? A taxi to Yeovil from Chetnole is fine, except you will probably find the train has left 10 minutes before and you have to wait 2 hours for the next one.
Commuters in the Bristol area have suffered for years.
It's not all doom and gloom, it's just lots of little niggly things that generally add up to a poor experience. It also gives the impression that management at GWR simply don't care or have given up. Lots looks to have been done with minimal cost; paint is flaking off the arm rests on the repainted 158s/150s. Some not yet livered 800s have stains on the grey fabric on the seats. The PIS is unreliable on every single class of train they operate. That said, internally the 158s seem a lot lighter now the blue/purple has gone. I can see why they wouldn't want to spend more they they had to as they may not still have the franchise in a few years.
I'm not going to complain about the 800s too much as they were DfT specified but all I will say is the seats are uncomfortable. I am fairly tall so if sitting with good posture, my shoulders are against part of the head rest which means I have to lean forward. And if I slump, my knees go into the back of their chair in front. I'm not a fan of the seating on HSTs, but at least I can sit up straight on those.
Despite being pretty horrific units for reliability, the 180s were great for comfort with seats that provided good back support (despite being fairly thin) with plenty of leg room. I don't mind the ironing board seats on the 387s for short distances.
I don't know a great deal about the Thames Valley. I know there are issues but to be honest I've only made a few journeys in the area. They were average at best but there does seem to be some congestion problems during the peaks on the Cotswold line.
On the whole, the ground staff are good. The issues on GWR's side appear to be from issues with management higher in the franchise with regards to staffing, maintenance, quality control, planning and future planning. Not to mention a few previous blips with their marketing.
I've waffled a bit but as I'm half enthusiast, half commuter and I definitely think GWR do better with leisure travelling. I don't think there are any quick fixes for Bristol but hopefully improvements will come. GWR inherited Bristol locals from Wessex but there were almost certainly issues then too, but due to the nature of how congested our cities are with more people choosing rail, this has definitely worsened in recent years.