Tom Anderson wrote:
On Tue, 24 May 2005, Clive D. W. Feather wrote:

In article , Tom
Anderson writes

The discussion says that something called a '4-track relay terminal
with a 2-track relay' used to exist at Park Row on the New York
subway. No idea what that is, but the poster seemed to be impressed.


####D####
/--------------\
|------* ####A#### \
\-----------\ /--*----
X
/-----------/ \--*----
|------* ####D#### /
\--------------/
####A####


I've just realised how to build a terminal with arbitarily high
capacity, provided you don't mind making your passengers choose between
an equally arbitrary number of platforms:

+-[--------+-]-\
### / [ ### / ] \-----
-----+ [ -----+ ] /----
\ [ \ ] /
+-[--------+-]-/
n

Where the bit in square brackets with an n at the bottom is a repeated
unit (think polymers!). Trains come in from the east (and why do trains
always come in from the east in these things?), run along the road at
the southern edge of the structure, then pick a bay to stop in, run in
on the diagonal approach road, get in, stop, exchange passengers, then
pull out on the diagonal departure road, joining the main road at the
northern edge and heading back out east. The point is, there are no
conflicting movements, and no contention for anything except the running
roads, so the terminal doesn't restrict capacity below that which the
line supports (provided you can do the diverges and converges
perfectly). Note that when n = 0, this is a normal single-track
reversing terminal, and when n = 1, it's rather like a Sao Paulo
terminal (but with more irritating platform layout).

I think you have to be rather clever about the order in which bays are
used to preserve even intervals between trains, though.

If you replace the reversing bays with through lines, you get a
multi-track loop:

/-[--+-]-\
/ [ / ] \
|# [ |# ] \-----
|# [ |# ] /----
|# [ |# ] /
\ [ \ ] /
\-[--+-]-/
n

Which is wider, shorter, doesn't reverse the trains and is amenable to
the use of island platforms.

Probably not the most sensible use of railway space, either way!

I take it you've never played Transport Tycoon. You've just described a
Ro-Ro station.

http://www.transporttycoon.co.uk/rail2


--
Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London