Tom Anderson wrote:

Thus, my point that the frequency at the suburban stations is too low to
be useful as a tube line stands, and moreover, Jon Morris's point, which
you've helpfully snipped, that "the service frequency from King's Cross
to Blackfriars makes it almost as good as any other tube line" is also
shown to be an outrageous lie - 8 tph is barely a turn-up-and-go
frequency, and not what i call tube frequency. Perhaps if you've been
unlucky enough to grow up out in the western branches of the Magical
District Line Tree, you might think so, but as someone who lives at
Finsbury Park, i don't.

Just as a point of comparison - several NYC subway routes run less
frequently than 8 tph during rush hours. And midday timetables on many
(most?) routes call for 6 tph.

To be fair, what's considered a single route in NYC might in many cases
be considered one branch of a line in London.
--
David of Broadway
New York, NY, USA