Not aimed at anyone in particular, but for general interest, information and no doubt some disagreement!
However Nexus has published strategies and plans that envisage such extensions to their network, cheaper than fully segregated metro spec and therefore more widespread and offering more benefit for a given budget, yet still able to access the city centre via the existing segregated network, to which such extensions and branches could add core frequency, and where there is capacity.
Some of these were branded as Metro and presumably would be integrated for ticketing and marketing purposes but in technology terms would be standard street tramways with no track connection to the existing Metro network. This was certainly true of the Metrocentre route as proposed in mid-2013, though I don't know what has happened to it since then.
Phase 1 also saved a lot of expense by not completely rebuilding most of the stations it took over. High floor light rail systems with some street or roadside reservation running are fairly common in Germany and indeed the 1st generation high floor DLR cars returned to their fatherland to work such a route in Essen.
Most modern tramways have broadly followed German practice, as the major country that developed the mode after WW2 instead of abandoning it. The below also applies in particular to some of the surrounding countries.
Up until around 1990 the state of the art vehicle was high floor with about three steps down to each entrance door. From the 60s onwards various cities developed their tramways into effectively Metros with largely segregated track often underground, or the "pre-Metro" concept of just building the central area tunnels for the time being. For accessibility reasons these networks usually had level boarding from high platforms, and where low platforms were still served the vehicles were fitted with floor sections that unfolded to reveal steps.
As I mentioned above, the low floor tram became viable in the 1990s and practically every order since then has been low floor, except for networks that were committed to high floor operation. Low platforms are much easier to build in urban areas and the low floor tram provided an equal level of accessibility without having to find room for high platforms at every single tramstop. This helped those cities that hadn't yet put their trams in tunnels to make way for car traffic to adopt the better policy of keeping the trams visible and accessible on the surface and restricting other traffic instead.
The UK followed the same trend but on a much more limited scale. Tyne and Wear in the 70s and DLR in the 80s mirrored contemporary German high floor practice, creating the only public transport in the country that could be used by wheelchair users without assistance (the third rail DLR needed high platforms for safety reasons in any case). Metrolink did the same but with the added element of street running. However pretty much every new network planned in any country since the advent of workable low floor tram designs has opted to use them, except those that are fully segregated.
And that's a reason to consider high floor standards for new systems where inter-running with heavy rail is more likely, or when it could reduce costs by avoiding parallel infrastructure. High or Low platforms is 'horses for courses' really depending on the circumstances, especially when beginnning to develop a network. Early Metrolink didn't have to build too many new stations so the total cost of high floor throughout was low*. In Sheffield, the Rotherham extension is a fairly short heavy rail extension to an already established low floor network, so the tram trains have to be low floor too. There's only one shared station planned for which split-level platforms are cost effective and practical.
Agreed. But I don't think there will be many if any new high floor tramways. The only on in the UK I think is remotely likely is Cardiff. If the Valleys are converted to tram or tram-train with relatively small extensions from the existing network, and none in central Cardiff, then high floor might be a good choice. But elsewhere, lowering high platforms isn't a huge cost in the context of a light rail scheme. And while providing dual-height platforms at a few tram-train stations can be tricky, it is a lot less so than trying to integrate high platforms into a street environment.
T&W want to buy additional and replacement vehicles to full road legal tramway configuration, but otherwise with identical size, performance and internal layout as the 1st gen metro cars, although perhaps sacrificing passenger forward view, as line of sight operation needs excellent wide angle vision for the driver and that usually places the cab out in front of the passenger compartment in modern designs. These units could use block signalling when on core parts of the city network, yet also could run off onto new extensions with roadside reservations, short street sections and level crossings, all using line of sight tramway methods. Their ability to run under standard metro block signalling (or its future modern replacement) in the tunnels could also allow the units to run on suitably cleared and equipped National Rail infrastructure, just as the 1st gen units do today. Nexus seem to have a practical migration strategy that could lead to cheaper extensions and a standard go anywhere 'tri-mode' tram train vehicle. The small price Nexus will pay is that the light rail extensions will have to be built with high platforms, yet the increase in construction costs for new sites is fairly small and could encourage wider stop spacing, which can help with average speed and thus more attractive journey times for longer trips.
This was certainly the case for the abortive "project Orpheus" around 15 years ago but as I suggested above it is perhaps less so today. However the existence of the German and other high floor networks does mean that modern high-floor tram designs are reasonably readily available. The spec for the future Metro vehicle you refer to is pretty much identical to the Metrolink M5000 vehicle with the exception of line voltage. Traction packages can easily be changed to use 1500V as well as 750V, but 25kV would need a transformer and probably result in a longer vehicle to make space for it.
Where it gets more tricky is if tram-trains are required to conform to an increased structural strength standard (but still less than that of trains) as suggested by recent European developments. All tram-train routes in other countries are medium or low floor to match their heavy rail platforms, their high floor networks being pure light rail with no track sharing. So a high-floor tram-train could become a much more costly non-standard design.
