Alstom and CAF don't yet make a BB cab module on this platform. Hardly
anybody does because there is so little demand for trams under 30 metres.
BB cabs like the one I illustrated above for Ostrava are produced by some
German and Czech manufacturers for bespoke orders for smaller cities (like
Ostrava) where they want a tram shorter than 30 metres. This type of
configuration has generally replaced the Jacobs bogie, I don't understand
why. That's probably the context in which you saw a concept design. Bigger
cities are now increasingly heading north of 30 metre lengths as demand
rises - 30 metres is the new minimum, so there's a bit of design fudging to
get a shorter length.
These various module combinations with their odd distribution of bogies
also play havoc with both positioning and number of doors. It's like some
great dumbing down of basic principles learned over decades earlier.
Speaking of Jacobs bogies, the Skoda 15T is ideal for this sort of
expansion, having the right module dimensions to evenly expand from 20
something metres to 60 or whatever - upholding the even two-door-per-module
distribution going no matter the length. The SIemens Avenio, although
having the bogie in the middle of saloon, likewise enables two
evenly-spaced doors per module. These two trams are the apex of swivelling
bogie designs (though the swivel on the Siemens is very limited) and would
be excellent for Melbourne, also for their flexible expandable lengths.
However, I think why Alston and CAF are shortlisted is that they're willing
to locally assemble, whereas Skoda and Siemens are probably not.
On Monday, 3 May 2021 at 20:41:04 UTC+10 Matthew Geier wrote:
> On 3/5/21 4:49 pm, TP wrote:
> > That would be a very untidy extension with a mixture of lengths, some
> > requiring two bogies, and random door placements.
> I've seen what was probably a concept design, and i can't remember
> where, a tram with a 2 rotating bogie end section and then a number of
> single bogie modules 'hanging' off it. It doesn't have to stop at just
> a single articulation and 3 bogies.
> Normally a ~30m version would have 2 single bogie end sections hanging
> off a 2 bogie centre section, but it doesn't have to be a B+BB+B
> It could be a BB+B+B, so you could stick a 10m long middle into a single
> articulated 20m version to lengthen it.