Neil Williams wrote:
On 2017-04-27 20:42:58 +0000, Recliner said:

Very little (10%) of the Newcastle Metro is underground. It's much more of
an S-Bahn than a U-Bahn.

An U-Bahn doesn't have to spend that much of its length underground,
plenty of the Hamburg system is above ground, including the comedy bit
where the U-Bahn (Hochbahn) is elevated and the S-Bahn underground.
The distinction is mo

U-Bahn: segregated light rail metro, not on "national rail" (DB)
tracks, no level crossings.
(Subcategory: Stadtbahn: branded U-Bahn but is more of a souped up tram
system with an underground bit in the city centre. Very much like what
Metrolink would be if it had a city crossing tram tunnel)

S-Bahn: heavy rail metro, runs on DB tracks, can have level crossings
and interworking with other mainline services but doesn't necessarily.

Which leaves LU a bit of a curiosity, being an U-Bahn by all
definitions except that it's heavy rail, though the Met is really an
S-Bahn in character. The Newcastle Metro, being light rail, is a
textbook U-Bahn. Merseyrail is near enough a textbook S-Bahn.

Though, of course, the Newcastle Metro largely runs on former BR tracks,
and it does share NR tracks with heavy rail, making it more like an S-Bahn
in that respect.

http://www.thetrams.co.uk/tyneandwear/sunderland/