On Thu, 18 Aug 2005, David Spiro wrote:

"Tom Anderson" wrote in message
h.li...

Another interesting difference is the almost complete lack of
underground line in south London - here, the suburban surface rail
network was very well-developed early on (and extensive urbanisation
was later than in the north, i think), so the need for tubes never
arose. I don't know if there's a a parallel in New York - are there any
boroughs with surface rail lines rather than subways?

Well, in the Bronx where I grew up, some of the lines, such as the #6
are almost completely above ground, though it does go under for about
the last quarter of it's journey before going into Manhattan, which is
completely below ground. The only other line that I am familiar with
that is just about all above ground is the #7 Flushing line train, which
only goes below ground at its eastern terminus at Main Street in
Flushing. On the whole, the system is a mix of both above and below
ground service. Even in Manhattan, the #1 Broadway local train is on an
elevated section through a part of Harlem, the last elevated subway in
Manhattan, albeit for a short stretch.

I see. I guess the difference is that the subway and above-ground bits
were built by the same companies, as two ways of building lines, as
necessary. In London, we had one lot building mixed lines in the north,
and another lot building purely above-ground lines in the south - the
distinction survives today, as the lines are operated by entirely
different organisations.

In fact, the really important distinction between north London's
underground and south London's railways is not their altitude, but their
topology: underground lines usually consist of a central section with one
or two limbs at each end, so they can easily run a high-frequency service;
the railways, however, generally have many more branches, and interconnect
into a complex network, making it impossible to deliver high frequencies
at the outer ends. I have no idea why it worked out like that; perhaps
because it's so much easier to add branches to an existing surface line
than it is to add onto a tube. Socio-economic factors are probably also in
there somewhere.

Also, of course, the underground lines all run under the centre, whereas
the railways all stop at termini just outside the city centre (apart from
Thameslink). You might think that's a physical thing - after all, you can
hardly drive surface railways through central London - but the thing is,
there are north London surface railways (there are a handful of these;
it's not all tubes!) that did it. The Great Northern & City railway
planned to do it as early as 1891 (although it didn't _quite_ happen until
the 1970s!), and around the time of the first world war, the London &
North Western Railway managed to hook its line up to the Bakerloo tube
line. Now, the southern end of that line is at Elephant & Castle, which is
pretty close to a number of southern railway routes, so i really don't
understand why none of those were joined up to it.

tom

[1] Or whatever it's called - Great Northern Electrics, Northern City
line, Moorgate line, etc.

--
On two occasions I have been asked [by members of Parliament], 'Pray, Mr.
Babbage, if you put into the machine wrong figures, will the right answers
come out?' I am not able rightly to apprehend the kind of confusion of
ideas that could provoke such a question. -- Charles Babbage