Ken wrote:

Most European countries find both of them very useful.

The main thing that prompts them to use DD trains is to save money.
They tend (TGV Duplex excepted) to end up largely on short regional
trains that could easily be made longer for that reason. This even
happens in countries like Germany where low platforms mean that longer
platforms are cheaper than the UK.

Bendy buses are a different matter, and their suitability for, say,
German-style operations has a different reason behind it. In a typical
large German city, there exists an integrated public transport system
with sufficient capacity on all modes and a good distribution. Thus,
the purpose of a bus is to move people in the areas not served by rail
rapid transit of whatever type to the nearest station on such a system.
There are comparatively few bus services that penetrate the city
centre compared with London, and most of those are rather short
distance runs.

In the UK, by contrast, it is common for buses to provide a through
service from a location not served by rapid transit rail (of whatever
type) to the city centre. Outside London, this is often a competitive
service. This means longer journeys by bus than would be typically
seen in the mainland European city. This, in turn, means that people
are more likely to be bothered about wanting a seat.

The double-decker bus, therefore, is more suited to such a situation.
It means that the long-distance travellers can take a seat in the upper
deck, while anyone taking a short journey can remain on the lower deck
in a similar low-seating configuration to the bendy.

To apply the question to London, then - yes, long-distance routes are
better with deckers. Whether the aim should be to move to a European
interchange model or remain with a British through service model is
another, rather more difficult, question. However, there are routes
where bendies are more suitable, potentially with the appropriate
infrastructure changes. I'd certainly nominate Oxford Street - but
then on the European model, it also needs fewer routes (maybe only
one?) and interchange at convenient points at each end.

There is one more factor. It is my understanding that the standard
bridge height in most European countries tends to be lower than the UK,
thus DD buses don't necessarily fit. They (and some pretty huge ones
by the typical UK standard) do exist, however - in Berlin, for one.

Neil