Am 15.01.2012 13:28, schrieb Wolfgang Schwanke:

I ask, because I noticed that some tracks simply stopped short of the
border, literally cut, when I visited Berlin in 1999,

Do you remember the exact place you were then? The U-Bahn system has
been restored to its pre-wall status in 1995 with all previous
cross-border connections operational.

So I think that this "1999" is a type, originially meant "1989".

When U2 was reconnected in 1993, polarity on the third rail had to be
reversed on its eastern half, because they'd altered it for some reason
in the east.

That is another difference between the large and narrow profiles --
the older one, i.e. the narrow profile, touched the third rail from
above, the newer one, i.e. the wide profile, touched it from below, as
the S-Bahn does. This is the safer option, and probably they changed
this for exactly that reason. Maybe it enabled also the narrow profile
cars to be used on the wide profile line E (today U5), just with
"Blumenbretter" (window sill) attached under the doors in order to
bridge the gap between car and platform, just as they did in Pyönyang,
to add a detail to the next question below:

They must have adapted it. As Pyongyang ran both small profile "Gisela"
as well as large profile "D" at different stages, who are incompatible
with each other, they must have made mechanical and electrical
adaptations at least for one of the two types, or even both.

There is at least at one point in the web (or was) a page with
information on this.


Cheers,
L.W.