I think that this is an eminently sensible suggestion. The use of such elevated alignments has stood the DLR in good stead.
Apparently not, they are available with diesel engines but the TfW units will only be battery-electric. Some of the Stadler Flirts are diesel electric only, some are trimodes (diesel electric, overhead lines and battery)
TfW/Keolis Amey have never explicitly given a reason for why the Rhymney line is getting heavy rail Flirts, and not the tram-trains. The tram-trains would definitely be better suited to the Coryton line than the HR Flirts.
I think it might be the other way round, that the Rhymney line is paired operationally with the diesel lines to the south because that line will use the Flirts. If there had been a need to use the Flirts on the routes via Pontypridd then those could have been through-routed instead.
Cardiff Parkway is a live project, with 4 platforms planned. That will go ahead whether or not the tram train project ever happens. The tram-train project is described as an "ongoing study", part of which will no doubt include provision for terminating services at Parkway, which as you suggest would sensibly include a further platform. So long as the current planned project retains space for a further platform, presumably to the south of the existing tracks, then I don't see the two are incompatible.
No great surprise that Drakeford hasn't got a clue........
The units on the T&W Metro are not trams; they're basically lighter trains, but they don't run on streets at all. A better comparison is the Sheffield Supertram, where the tram-trains there run on both streets in Sheffield and on heavy rail lines through Rotherham.
A further platform isn't necessarily needed, as a turnback siding could do the job, and there'd be space between the mains and reliefs, they'll need to be slewed to make space for the island platform anyway, so why buy extra land when you've got the space already.
A siding between the mains and reliefs would be operationally inconvenient, as you would then need to wait until both relief lines were clear before crossing over back onto the down relief line. The most sensible place for a turnback siding is in between the two relief lines, which removes any conflicts. However, if the service is relatively frequent then surely you want to try and minimise movements, so going straight into a dedicated platform and back out again would be more efficient. Even better if that is also between the two relief platforms, but unless that is being designed in now that would be too disruptive.,
Turnback sidings aren't operationally inconvenient, it'll be planned so it fits. The best place for one isn't between the reliefs, as that would mean even more slewing of track and taking up extra space. Between the mains and reliefs it fits in to space that's already there.
Although the original T&W Metrocars, built by Metro-Cammel, are not equipped with the lights, indicators and more comprehensive side skirting that could allow street running, they are otherwise based very closely on the German tram design known as 'Stadtbahnwagen Typ B', developed by Duewag and used, in large numbers, in Köln and Bonn, Essen, Dortmund, Düsseldorf, Duisburg, and Mülheim. From the point of view of crashworthiness for inter-running with mainline passenger rolling stock and freight on the Sunderland line, the vehicles were considered equivalent to trams, so extra protective measures were incorporated in signalling infrastructure and controls. Both TPWS and the Metro's own (German) Indusi-based protection systems were provided at each and every signal along the route, with overlap lengths and differential speed restrictions for the varying traffic types adjusted to reduce collision risk. As such, Sunderland can be seen as perhaps the first UK tram-train scheme, even if it was never referred to as such at the time.
The one at Maidenhead, which is the one regularly used by a frequent metro-style service, is situated between the relief lines, which is the closest analogy to the likely use at Cardiff Parkway. The other two are barely used by passenger services in normal operation if I'm not mistaken, so I don't think they are at all relevant.
Moving a few signals would not be a great expense in the whole scheme I'd suggest. With the comparatively short trains planned, there's scope for moving signals on the metro lines further back from the platform ends to make room for a new junction with free overlap clearance. There was a junction on this site leading to a parcels platform in years gone by. I assume if necessary the PSB building can or already has been removed.
The "old" platform 8 junction was the spur that used to be in front of the PSB (I believe)
The southern-most platforms at Cardiff General station were designated as Cardiff Riverside station and used by the Barry Railway on services to Barry and Pontypridd/Porth via Creigiau, as well as the Taff Vale Railway for some services to Penarth (and Cadoxton via Sully). On weekdays (0800-1800) and Saturdays (0800-mid afternoon), these trains were generally extended via the Riverside branch to Clarence Road station, rather than Bute Road station (which was the main terminus of the Taff Vale Railway).
Thanks for the clarification! Couldn't quite remember
Fair point - I personally wouldn't view them as tram-trains (since they don't run on any streets, at all) but I see your logic. The design is certainly derivative of trams, although you could probably say most forms of rail-based transport derive from each other in one way or another!
