Dave Arquati wrote in message ...

Perhaps 1 in 4 passenger from Ebbsfleet, Grays, Basildon, Chelmesford,
Stansted will want to go beyond Liverpool St to Farringdon, TCR, Bond
Street and beyond. Therefore CrossRail should provide 1 in 4 of the
lines into Liverpool Street on each of these routes. That is, 4 tph,
with 12 tph terminating at Liverpool St.

This is logical thinking but there's a big flaw. At least to start off
with, the same number of passengers will still be using Liverpool St
regardless of whether 1 in 4 or 4 in 4 trains are Crossrail. In fact
Liverpool St will overall have more capacity.

I'm not sure if I follow.
- More passengers will be using Liverpool Street because capacity and
usefulness of Liverpool Street will be increased.
- Many of these passengers will stay on CrossRail trains and go
straight through.

Both of these are benefits. The second is only a benefit to commuters
wanting to continue West from Liverpool Street, which is probably a
(large) minority of passengers. (Though the number will increase as
working and living patterns change)

We could assume that whether 1/4 or 4/4 of Shenfield trains are
Crossrail, the same number of people are using Liverpool St Underground
station - and that number will be a reduction on 0/4 Shenfield trains
being Crossrail.

Agreed and ditto if 0/4 Bishop Stortford, Grays etc trains are
CrossRail.

However, other Crossrail trains are now arriving at Liverpool St from
Basildon and Grays - some of these passengers would have used Fenchurch
St instead but perhaps Liverpool St is nearer to their workplace, or it
makes no difference whether they arrive at Liverpool St or Fenchurch St
so they just got the first train that came along.

This is placing *extra* demand on Liverpool St.

Matched by the extra capacity.

Looking at it another way, Crossrail will free up a lot of capacity in
Liverpool St mainline for other services - for example new fast services
from Brentwood.

Depends on where the bottleneck is. Is it the station, or is it the
incoming lines? (though the Isle of Dogs line is mostly new and will
provide extra line capacity).

These services will be attractive to Brentwood
passengers heading to the City, and they will use these in preference to
Crossrail - so those passengers carry on using the mainline station as
they were before, but with a faster and probably less crowded service.
If the numbers of people using Liverpool St Crossrail were a problem,
this would help to balance that problem out.

Agreed. But how does this suggest that spreading CrossRail out to
five* branches, each of 4 tph, is not the way to maximise CrossRail
benefit?

*This makes 20 tph, compared to tunnel theoretical capacity of 24 tph.
I would then have train waiting at Liverpool St and Paddington to fill
any spare slots caused by late arrivals. These would only go Liverpool
St to Paddington, and make up the numbers to 24 tph.

Dave Arquati wrote in message ...

You said that "if Shenfield is only served by CrossRail, then at
Livepool St most of the passengers will want to get off, adding to
passenger congestion."

It's a fair point but as you say, Liverpool St's capacity will be
increased. Crossrail's design will take into account the fact that a
large proportion of passengers will disembark at Liverpool St, so
congestion (I assume you mean on the Crossrail platforms) should not be
a problem. These are *big* stations - don't forget there will also be an
exit at Moorgate, so some Shenfield line passengers will use Liverpool
St Crossrail but not Liverpool St itself, if you see what I mean.

Yes, but the I would expect the bottleneck to be on the train itself,
as all the passengers arriving at liverpool St from other lines now
try and get onto CrossRail trains at liverpool St, just as 3/4 of the
train is trying to exit. With all trains going to just two locations,
I'd expect 50-75% of the train contents to change (ie exit and enter)
at Liverpool St, increasing the platform time and reducing the
throughput.

A solution would be, as in Munich, to have double sided access.

However, the problem to note is not so much that a majority of
passengers will disembark at Liverpool St, but that running all
Shenfield trains as Crossrail reduces operational complexity, which will
in turn increase reliability and allow a high frequency to be achieved.
If some terminate at Liverpool St mainline, this increases the number of
movements across a junction which could cause problems.

Agreed, that's the trade-off. Most of the other lines would join at
Stratfiord, so one flyover there would ease this particular problem.

snip

Five branches means huge operational complexity and extra cost - unless
they all have flying junctions then that adds conflicting movements,
which means reduced reliability.

Not all, but only near the "root" - probably one at Stratford.

How do Grays trains get to Crossrail? There are a number of options but
they are either expensive or reduce reliability on existing lines. For
example, they could run from Stratford to Barking via Woodgrange Park -
but so do a large number of freight trains from Tilbury, which all have
to cross flat junctions. Or they could surface near Bromley-by-Bow
instead - but that means extra tunnelling and an underground flying
junction. Similar arguments may apply to any other branches.

*This makes 20 tph, compared to tunnel theoretical capacity of 24 tph.
I would then have train waiting at Liverpool St and Paddington to fill
any spare slots caused by late arrivals. These would only go Liverpool
St to Paddington, and make up the numbers to 24 tph.

This would require turnback capacity at Liverpool St (which will be more
expensive) and extra platforms at both Paddington and Liverpool St
(which will also be more expensive - particularly at Liverpool St which
I think will be bored).

Also, how do you decide when an arrival from the surface routes is late?
Say trains must be separated by at least 75 seconds, and each "slot"
is 150 seconds (2.5 minutes = 24tph). If the previous train departs into
Central London right near the end of its slot, then the next train
cannot depart until 75 seconds into the slot.

Once those 75 seconds have passed, how many of the next 75 seconds do
you wait before the due arrival is considered "late", given that it will
also take a reasonably "long" time between deciding to despatch a train
and it departing the station, given that passengers have to realise that
a train is about to depart and to board it.

This all depends on being able to predict the lateness a few minutes
before it happens. With some smart IT and train positioning systems,
this should be possible.

What happens if two consecutive trains are late? You won't be able to
get a new train ready in 150 seconds, e.g. at Paddington - even if the
new train is waiting in turnback sidings at Westbourne Park and departs
for Paddington as soon as it is decided to despatch the standby train
already in Paddington. In fact the second late arrival may already have
passed Westbourne Park.

If you don't have it, you get bunching. A late train is a more used
train, which increases platform time, which makes it later. On buses,
this is solved when the following, empty bus overtakes, and hoovers up
all the waiting passengers. On CrossRail, a fast response insertion
would do this.

Although I like the idea of standby trains, the more I think about it,
the more it seems unfeasible for a high-frequency service.

Depends on being able to have 3 minutes warning of lateness (or a 5
minute gap)

Roland Perry wrote in message o.uk...
In message , at 23:54:01 on Wed, 4 Aug
2004, Mark Townend remarked:
I can remember standing on the westbound Central Line platform at
Liverpool St in the morning rush hour in the mid-80's, and you could
routinely see the front of one train entering the station at the same
time you could still see the rear of the previous one departing.
--

So illustrating platform reoccupation time as the fundamental limit on
capacity.

Consider the length of the platform as the braking distance for a train
entering the station at 'station entry' speed then the back of the train in
front must have just left the station (plus some additional 'overlap'
distance - see below).

The Central Line trains I observed were entering the platform at a
relatively slow speed. Perhaps 10mph. Common sense, if not signalling
practice, means that they could get within a couple of carriage-lengths
of the back of a departing train without any ill effects (although they
were perhaps 3/4 of a train away). After all, that's just what busses do
at every single busy bus stop, and they rarely rear-end one another.

It's only trains that have this concept of needing enough of a gap to be
able to stop blind from full speed.

Being able to key by a signal at danger (and proceed at caution)
allowed the NYC subway to run some very frequent services.
Unfortunately, a few years ago, there was indeed an accident which has
led to this practice being abandoned. What happened was that a train
was following another train over the Williamsburg Bridge, which is a
suspension bridge and consequently has quite severe grades at either
end. The second train reached the crest of the bridge and started to
coast down. Meanwhile the other train stopped and the second train's
brakes weren't good enough to stop on the downgrade. Result:
futtbucked. I still think that the abandonment of keying by was a
mistake - the practice should just have been restricted a bit better
to avoid such close following on downgrades.

In article , Mark Townend
writes
So illustrating platform reoccupation time as the fundamental limit on
capacity.

Consider the length of the platform as the braking distance for a train
entering the station at 'station entry' speed then the back of the train in
front must have just left the station (plus some additional 'overlap'
distance - see below). The platform is a single occupancy block however
[...]
More modern 'speed-band' control systems like LUL Victoria and Central lines
achieve a similar effect, but can't overcome the platform reoccupation
limit, though can allow the maximum service frequency to approach the
theoretical limit more closely.

Both the Central and Victoria Line systems allow a train to be entering
the station while the previous train is still leaving. This is because
the platforms aren't "single occupancy block"; they're subdivided.

This is more obvious on the Central Line; you can see the block
boundaries along the platform, marked by a white board carrying a red
diagonal stripe. In both systems the train's speed is controlled to
ensure it will stop before hitting the previous train.

--
Clive D.W. Feather | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Please reply to the Reply-To address, which is:

In message , Clive D. W. Feather
writes

This is more obvious on the Central Line; you can see the block
boundaries along the platform, marked by a white board carrying a red
diagonal stripe. In both systems the train's speed is controlled to
ensure it will stop before hitting the previous train.
This is not new. Before the 70s we had 5 signals approaching a
station, the first released when you were down to 25, the second when
you were down to 20 and the next three released as the previous train
left the platform, with the last one releasing when you had a car's
length inside the platform and the original train still had a car in the
starters overlap.
This was common on both the Central and Northern lines.
The others I didn't work on and cannot therefore comment on.
--
Clive

Thanks, David. I've managed to find the relevant thread on SubTalk:

http://talk.nycsubway.org/perl/read?subtalk=713864

:-( I go away for two weeks, then SubTalk's down when I get back!!!

"David Fairthorne" wrote in message .cable.rogers.com...
Excellent answer, James.

The station that you describe in Sao Paolo is Cornithians-Itaquera on line
3.

"James" wrote in message
m...
Depends on where the bottleneck is. Is it the station, or is it the
incoming lines? (though the Isle of Dogs line is mostly new and will
provide extra line capacity).

Most likely the station. Lines can carry X tph (where X is quite high
and depends on signalling and junctions) - but a terminus station can
only accept and despatch a certain number of trains due to its layout.

Look at the Victoria line. Presumably signalling can take the frequency
up to a high level (I believe 40tph was once achieved on the Central
Line a long time ago?) but terminal capacity (specifically the scissors
crossover) will limit this frequency - adding a loop past Brixton would
enable a higher Victoria line frequency because the terminus is
essentially eliminated.

There are essentially three terminus arrangements which maximise
frequency:
(1) The single track loop (eg Kennington and Heathrow in London, South
Ferry and City Hall on the IRT in NYC) - as you say, abolishing the
terminus - the problem is that this removes the layover point and
therefore doubles the length of the route, making the line more
susceptible to disruption.
(2) The multiple track loop (eg WTC station on PATH, NYC) - this
allows a certain amount of layover time to even out outbound service.
(3) A three track, two island platform terminal, where the following
moves happen (where track A is from the inbound track, track B is a
bay in between the other two, and track C leads to the outbound
track):
(i) train arrives on A
(ii) train arrives on B, train on A proceeds to turnback siding beyond
station
(iii) train departs from B, train in turnback siding pulls into C,
another train arrives on A
(iv) train departs from C, train arrives on B, train on A proceeds to
turnback siding beyond station... etc...
This third layout is only found at a station in Sao Paulo whose name
totally escapes me at the moment. A similar layout used to exist at
the BMT's Park Row El terminal in Manhattan (demolished in the 1940s -
so much for progress...)

Actually the highest frequency on a two-track line I've ever come
across is the original cable-hauled shuttle service (1883-1908) across
the Brooklyn Bridge (Sands St, Brooklyn, to Park Row). It ran 90 (yes,
ninety) tph peak, and averaged 40tph over a 24 hour period. I think
that if we saw their operational practices in use these days, we'd
have a fit, but nevertheless it goes to show what can be achieved with
decent terminals and without such useless objects as a signal system
;-)

At one time frequencies like 40tph weren't at all uncommon. Now you
only get them in Moscow, Sao Paulo and a miserly 36tph in Paris.
Indeed, the only thing which tends to restrict a 2-track line to 40tph
is the line staying two-track in stations. Once regular el service
commenced over the Brooklyn Bridge in 1902, the Sands St station had
four platform faces in service, with one two track line continuing to
Manhattan and two two/three track lines feeding in from various parts
of Brooklyn (these lines sub-divided further into about ten branches -
you can guess how intensive service would end up being!).

Less trains running into Liverpool St mainline = more platforms and
fewer movements across the approach junctions. This could be used to
improve reliability or add services (and here I suspect
adding services will generate more revenue than improving reliability)

Flat junctions aren't necessarily bad - you just need to time them
right. The junction at Sands St was a flat junction.

Agreed. But how does this suggest that spreading CrossRail out to
five* branches, each of 4 tph, is not the way to maximise CrossRail
benefit?

Five branches means huge operational complexity and extra cost - unless
they all have flying junctions then that adds conflicting movements,
which means reduced reliability.

Flat junctions can work on two track lines. They're only an absolute
disaster on three and four track lines (which is why they're so
necessary on the SWML). The ideal situation is to have the inbound
branch and outbound branch trains passing through the junction at the
same time. On branching systems, however, capacity is rarely an issue
once outside the central area. A flat junction where two lines at 4tph
merge, for instance, is not going to cause many "bangs" (trains will
be on average 7½ minutes apart (front to front) over the section with
conflicting moves - which with 600ft trains at 20mph will have an
occupation time of 20.45 seconds, still leaving over 7 minutes gap).
Even in a situation with lots of "bangs", service reliability can be
maintained by providing a third track just before the flat junction,
so that an outbound branch train waiting for an inbound main train to
pass won't delay an outbound main train (another thing which just so
happened to be a feature at Sands St... these Brooklynites knew what
they were doing...).

How do Grays trains get to Crossrail? There are a number of options but
they are either expensive or reduce reliability on existing lines. For
example, they could run from Stratford to Barking via Woodgrange Park -
but so do a large number of freight trains from Tilbury, which all have
to cross flat junctions. Or they could surface near Bromley-by-Bow
instead - but that means extra tunnelling and an underground flying
junction. Similar arguments may apply to any other branches.

Freight trains are something to avoid running on metro systems. They
are an unmitigated disaster (remember the Southern Electric's rush
hour freight embargo - they had their priorities straight there). If
they must be run, they should have a separate track or run between
2000 and 0600 (and on more lightly used sections also between 1000 and
1500).

*This makes 20 tph, compared to tunnel theoretical capacity of 24 tph.
I would then have train waiting at Liverpool St and Paddington to fill
any spare slots caused by late arrivals. These would only go Liverpool
St to Paddington, and make up the numbers to 24 tph.

This would require turnback capacity at Liverpool St (which will be more
expensive) and extra platforms at both Paddington and Liverpool St
(which will also be more expensive - particularly at Liverpool St which
I think will be bored).

A clear argument for making them Westbourne Park to Bethnal Green or
something instead. However, I see the flaw in this idea as being that
the delays are most likely to happen between these points.

Although I like the idea of standby trains, the more I think about it,
the more it seems unfeasible for a high-frequency service.

It has been done before on the IRT in NYC. It was the subject of a
budget cut.

(James) wrote in message . com...
Thanks, David. I've managed to find the relevant thread on SubTalk:

http://talk.nycsubway.org/perl/read?subtalk=713864

:-( I go away for two weeks, then SubTalk's down when I get back!!!

"David Fairthorne" wrote in message .cable.rogers.com...
Excellent answer, James.

The station that you describe in Sao Paolo is Cornithians-Itaquera on line
3.

What immediately springs to mind is that this looks very much like
Morden station. Of course, right now Morden is operated as a
three-track terminus that happens to have tracks continuing past the
platforms to the depot, but it could easily be set up this way -- all
the trackage to do it is in place. And unless I misremember, it is one
of the highest-frequency termini on the system (something like 23 tph
off-peak and probably more in the peak).

You'd have stepping-back issues and lack-of-ATO issues, but you could
easily do it with two drivers on board (one at each end) for the
reversal. And if the reversing siding (probably just one road in the
depot) is rated for passengers, you can do it even more quickly
because you don't have to check that everyone is turfed out at the
station.

What I don't know right now though is whether Morden is a bottleneck
at all, but the BAHN simulations and associated Excel spreadsheets
I've run suggest that it could well be.

In message , Alistair
Bell writes
And if the reversing siding (probably just one road in the
depot) is rated for passengers, you can do it even more quickly
because you don't have to check that everyone is turfed out at the
station.

ISTR that the LU policy of checking the train before reversing is not
because it's not safe for the passengers to be carried into the sidings,
but because they have a tendency to panic and do stupid things. This was
after the incident at Liverpool Street where a guy missed his stop and
got carried into the reversing siding, but instead of simply waiting for
the train to reverse and deposit him back at the platform, he went
running through the train, slipped while trying to cross between
carriages and got dragged underneath the train to his death.
--
Spyke
Address is valid, but messages are treated as junk. The opinions I express do
not necessarily reflect those of the educational institution from which I post.

Spyke wrote:
In message ,
Alistair Bell writes
And if the reversing siding (probably just one road in the
depot) is rated for passengers, you can do it even more quickly
because you don't have to check that everyone is turfed out at the
station.

ISTR that the LU policy of checking the train before reversing is
not because it's not safe for the passengers to be carried into the
sidings, but because they have a tendency to panic and do stupid
things. This was after the incident at Liverpool Street where a guy
missed his stop and got carried into the reversing siding, but
instead of simply waiting for the train to reverse and deposit him
back at the platform, he went running through the train, slipped
while trying to cross between carriages and got dragged underneath
the train to his death.

Exactly. "Doing stupid things" in obviously hazardous situations is one
reason why slam-door trains will be withdrawn in 2004/5 ... except of
course for LU's entire fleet! (Slam doors at the end of each car)
--
Richard J.
(to e-mail me, swap uk and yon in address)

In message , Richard J.
writes

ISTR that the LU policy of checking the train before reversing is
not because it's not safe for the passengers to be carried into the
sidings, but because they have a tendency to panic and do stupid
things. This was after the incident at Liverpool Street where a guy
missed his stop and got carried into the reversing siding, but
instead of simply waiting for the train to reverse and deposit him
back at the platform, he went running through the train, slipped
while trying to cross between carriages and got dragged underneath
the train to his death.

Exactly. "Doing stupid things" in obviously hazardous situations is one
reason why slam-door trains will be withdrawn in 2004/5 ... except of
course for LU's entire fleet! (Slam doors at the end of each car)

What would it take to fit Central Door Locking to the connecting doors
on LU's fleet, such that the doors automatically lock when the train is
moving. Many slam-door coaches on the continent have this feature
(though most are set to lock when the speed reaches 5mph, which is
probably too high for LU).
--
Spyke
Address is valid, but messages are treated as junk. The opinions I express do
not necessarily reflect those of the educational institution from which I post.