In message , at 12:28:33 on Mon, 21
Dec 2015, Clive D. W. Feather remarked:

Ely ------------------------------------ Peterborough
\
Ely ---------a-------------------------- Peterborough
\
*
\
b------c--------------- Kings Lynn
\ \
\ -------------- Kings Lynn
\
d------------------ Norwich
\
----------------- Norwich

Actually, a+c is a single lead junction, as is a+d. b is just a single
track junction.

A "single lead" junction consists of a crossover between the two main
tracks, a turnout from one track to the branch, and points merging the
two tracks of the branch.

OK, I wasn't aware if that subtlety.

As is fairly obvious, places like "*" are a monster bottleneck.

Actually, even worse is when the points just to the left of "a" fail in
the diagonal, rather than the straight position. (I've not seen it
happen in real life, but I have in simulation.)

It'd be worse if "a" failed towards Peterborough, wouldn't it?
--
Roland Perry

In message ,
wrote:
As Rupert would tell us were he here, the biggest problem is the level
crossings over all three routes north of the junction at Queen Adelaide.

The level crossings don't affect train operation.

The
planned extra trains make them an even bigger headache, hence ideas like for
an Ely North station there.

How does adding a station alter the (non-)effects of the level
crossings?

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

In message , Clive D. W. Feather
wrote:
Shepreth Branch Junction isn't a single lead junction, it's a double
lead junction. Completely different thing.

To clarify, there are three standard layouts for where a double track
splits (I've shown right-hand ones, but left-hand ones are equivalent):

(1) Double turnout:

----*-------
\
--*---X-----
\ \
\ \
\ \

Disadvantage: the diamond crossing is a derailment hazard at speed
unless you use switch diamonds, and has to be manufactured specially.

(2) Double lead:

----*--------
\
--*---*--*---
\ \
\--\ \
\ \

Disadvantage: requires space for three tracks for a short section, thus
needing more room overall.

(3) Single lead:

----*--------
\
--*---*--*---
\
*---\
\ \
\ \

Disadvantages: can't make parallel moves to and from the branch and
there are more layouts where a SPAD can result in a head-on collision.

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

In message , Roland Perry
wrote:
Actually, even worse is when the points just to the left of "a" fail
in the diagonal, rather than the straight position. (I've not seen it
happen in real life, but I have in simulation.)

It'd be worse if "a" failed towards Peterborough, wouldn't it?

Arguable. At least you can run the Peterborough service, which used to
be the busiest. If the crossover is stuck in the diagonal position, you
can't *and* you have to run the remaining trains on a single line
between Ely and Ely North Jn.

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
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In article , (Roland Perry)
wrote:

In message , at 12:28:33 on Mon,
21 Dec 2015, Clive D. W. Feather remarked:

Ely ------------------------------------ Peterborough
\
Ely ---------a-------------------------- Peterborough
\
*
\
b------c--------------- Kings Lynn
\ \
\ -------------- Kings Lynn
\
d------------------ Norwich
\
----------------- Norwich

Actually, a+c is a single lead junction, as is a+d. b is just a single
track junction.

A "single lead" junction consists of a crossover between the two main
tracks, a turnout from one track to the branch, and points merging the
two tracks of the branch.

OK, I wasn't aware if that subtlety.

As is fairly obvious, places like "*" are a monster bottleneck.

Actually, even worse is when the points just to the left of "a" fail in
the diagonal, rather than the straight position. (I've not seen it
happen in real life, but I have in simulation.)

It'd be worse if "a" failed towards Peterborough, wouldn't it?

And, in the Ely case but probably not everywhere, the tracks from Ely to Ely
North Junction are both bidirectional so the point to the left of "a"
failing wouldn't have such a drastic effect. All traffic could (up to a
point) use the down line.

--
Colin Rosenstiel

In article , (Clive D.
W. Feather) wrote:

In message ,
wrote:
Single lead junctions saved a lot of money so were a frequent value
engineering element. Indeed there are still junction arrangements using
them which save money compared to conventional double junctions but don't
have the bottlenecks. Shepreth Branch Junction is an example with no
conflicting moves using only 4 simple points:

Shepreth Branch Junction isn't a single lead junction, it's a double
lead junction. Completely different thing.

I would say it was a series of single leads to distinguish it from a
traditional double junction with two points and a diamond crossing.

--
Colin Rosenstiel

In message , at 22:19:37 on Mon, 21
Dec 2015, Clive D. W. Feather remarked:
The
planned extra trains make them an even bigger headache, hence ideas like for
an Ely North station there.

How does adding a station alter the (non-)effects of the level
crossings?

Rupert probably has more detail, but aiui the station would be part of a
much bigger scheme to create a direct Peterborough-Norwich route in the
open countryside north of Queen Adelaide, including moving the
trifurcation further north and removing what would otherwise have been
the one remaining level crossing.
--
Roland Perry

In message ,
wrote:
Shepreth Branch Junction isn't a single lead junction, it's a double
lead junction. Completely different thing.

I would say it was a series of single leads to distinguish it from a
traditional double junction with two points and a diamond crossing.

No. See previous post: that's a double junction or double turnout; SBJ
is a double lead.

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

In message ,
wrote:
And, in the Ely case but probably not everywhere, the tracks from Ely to Ely
North Junction are both bidirectional so the point to the left of "a"
failing wouldn't have such a drastic effect. All traffic could (up to a
point) use the down line.

Peterborough traffic can't: while up trains can use the down
bidirectional line, down trains can't use the up bidirectional line
because there's no crossover.

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

In article ,
() wrote:

After last Sunday's fiasco, more cancellations for lack of drivers on
Great Northern tonight, plus, I gather, some on Thameslink this time.

Are Govia incapable of retaining drivers? And how much worse will it
get before they do something more effective to retain their drivers?

So far their only response has been about how many drivers they have
in training. They won't be available to drive trains until some time
in the Spring at the earliest.

And now a similar GN non-service has been announced for tomorrow. It seems
all Foxton, Shepreth & Meldreth get is a taxi.

A few of the London trains are class 1, making the trip in as little as 66
minutes instead of the class 2s in 83.

Back to the future!

--
Colin Rosenstiel