54 | the rail engineer | december 2012
light rail
writer
David Shirres
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At
(Left) Tube cooling
unit at Green Park
Station.
(Right) Metro Line 1
unmanned train.
and London are Europe’s largest
P aris
cities after Moscow and rank amongst
the world’s greatest. Although both are
quite different, their size and populations are
similar.
Physicists in Brazil have compared the two
cities for accessibility using a computer
model of their street and underground
networks. This showed that Paris and
London have respectively 11,699 and 6,885
transport nodes. Generating thousands of
random journeys between these nodes then
showed Paris to be the more accessible. It
was felt there were three reasons for this:
Paris has 2.5 times more bridges over its river
than London, large parks impede movement
across London and shorter distances
between metro stations in Paris.
A tale of two Metros
The term Metro, universally used for rapid
transit systems, originated in either Paris or
London. Paris’s original Metro was operated
by “La Compagnie du chemin de fer
métropolitain de Paris”, soon shortened to
“Le Métropolitain” then to Metro. Some
believe the name was inspired by the world’s
first metro, London’s Metropolitan Railway.
London has both the world’s first sub
surface line (1863) and deep tube (1890).
London’s blue clay is ideal for tunnelling so
by 1906 it had four deep tube lines. Paris’s
first metro opened in 1900. With difficult
tunnelling conditions most Metro tunnels
were constructed by cut and cover. Also, in
contrast to London, the Metro generally has
two-way tunnels. London’s Underground
has 270 stations on its 250 mile network.
Paris’s network is much denser with 301
stations over 133 miles. Paris has the busier
network carrying typically 4.5 million
passengers a day compared with London’s
3.2 million.
The IMechE Railway
Division’s autumn technical
visit “Challenges of Metropolitan Railways”
was a great opportunity to learn more about
these two systems. This included a
presentation on cooling the tube and seeing
how King’s Cross tube station has been
transformed. Across the channel there was
an opportunity to learn about new
unmanned trains and handling large
passenger flows on Paris’s RER. the rail
engineer was there to find out more.
Cooling the tube
An old publicity poster proclaimed the
Bakerloo line was “the coolest place to be in
hot weather”. Yet today, cooling the tube is
one of Transport for London’s (TfL) greatest
problems. Its deep tube trains generate a lot
of heat which is difficult to dissipate as trains
occupy 67% of the tunnel’s cross section,
compared with typically 50% for other
metros. As shown by the old poster, over the
years this heat raised tunnel temperatures.
Train heat sources are: braking - 50%;
aerodynamic drag - 21%; motors - 15%;
electrical systems and auxiliaries - 13% and
passengers - 2%. Regenerative braking can
further reduce braking heat by a third.
This problem was particularly bad in the
2006 heat wave. Since then TfL has
implemented a programme on the Victoria
Line to reduce tunnel temperatures. Studies
made to consider engineering and
operational ways to reduce the heat
generated, determined that the optimum
train speed profile between stations had
high initial acceleration and longer coasting.
This has been programmed into the Victoria
Line’s Automatic Train Control (ATC) to give
significant energy savings and a 1.5 °C
reduction in tunnel temperature. Long term
engineering solutions under consideration
include supercapacitors to absorb more
braking energy and permanent
magnet motors which are more
efficient during acceleration.
Although air conditioning is now being
introduced on TfL’s sub surface stock, deep
tubes have limited space to dissipate heat
generated from the air conditioning units.
This would be a problem for stalled trains,
resulting in unacceptably high temperature
around them. One solution under
consideration is for trains to have
refrigeration units to produce ice when
above ground that would be used to cool
trains underground.
Specialist software was used to analyse
temperatures and air flows. This resulted in
projects to double the capacity of mid
tunnel shafts and, at some stations, to
provide water cooling.
Variable speed tunnel shaft fans have been
installed which need to cope with tunnel
pressure fluctuations and are reversible for
smoke control. They have baffles for noise
and tunnel dust, and operate at reduced
speed during start-up and at night. At 2.5
metres diameter, they are large fans and, as
access is through a one metre opening, had
to be assembled in situ. Between 2008 and
2011, all 13 Victoria line mid tunnel shafts
were upgraded resulting in a temperature
reduction of around 3°C.
Station cooling units are effective but
require a water supply. Two stations where
supply was available were Victoria (drainage
sump water for the underground River
Tyburn) and Green Park. Here a 100kW
cooling unit now uses 25 litres per second of
ground water at a constant 14°C. This is
extracted and returned to the aquifer by two
wells in the adjacent park. A detailed
analysis of heat pollution in aquifers, done to
gain approval from the Environmental
Agency, showed that these wells needed to
be at least 200 metres apart.
Water cooling at other stations and in
tunnels using 150mm pipes with fins is also
being considered. This would require water
to be cooled before
re-circulation.
december 2012 | the rail engineer | 55
light rail
One option is for TfL to do
this by selling its waste heat which could
provide a typical 10°C lift for hotel domestic
water supplies.
The problem of cooling the tube is not an
easy one. Nevertheless TfL has made a good
start in reducing tube temperatures. This is
an area with great opportunities for
innovation and it will be interesting to see
what solutions are adopted.
Below King’s Cross
Most people admiring King’s Cross’ new
concourse will not be aware that they are
standing on the roof of an underground
five storey building - the northern ticket
hall of King’s Cross tube station. This is only
part of an £800 million project to transform
the tube station which itself is part of a £2.4
billion spend to make King’s Cross / St
Pancras one of Europe’s largest transport
hubs. Re-development of Kings Cross
underground station was recommended
following the 1987 fatal fire and became a
necessity with increasing rail traffic, the
opening of St Pancras International and the
Kings Cross Development, not to mention
the 2012 Olympics.
The project started in 2001 and was split
into two phases. Phase 1, completed in 2006,
involved construction of a new Western
ticket hall under the St Pancras station
approach and enlarging both the sub
surface and deep tube ticket offices. It also
made a connection from deep tube lines to
the sub surface ticket office and provided
step-free access to sub surface lines. Phase 2
saw construction of the northern ticket hall
along with 300 metres of associated
pedestrian tunnels, 12 new escalators and
11 new lifts which resulted in step-free
access throughout the station..
Construction of the five storey box for the
northern ticket hall was a top down affair.
The first stage was driving side piles and
constructing the roof, whereafter the box
could then be excavated
underneath. This enabled
the surface to be handed
over to
Network Rail in September
2008 so that they could build their new
concourse. The new underground ticket hall
opened in November 2009. In addition to
the passenger areas, the ticket hall includes
a control room and areas for escalator
machinery, air handling, electrical
substations and fire control systems.
At the start of the project the station
served 55,000 passengers during the
morning peak. This figure is now 73,000 and,
by 2020, is expected to be 110,000. The old
station could not have coped with this
volume of passengers. That the contractors
transformed the station without disrupting
passenger flows was quite an achievement.
Automatisation de la ligne 1
Across the channel, Paris Metro’s Line 1
also has to handle large passenger numbers
and so there is a requirement to minimise
headway. Line 1 opened in 1900 and was
Paris’s first metro. It is also the busiest,
handling 725,000 passengers a day. For
various reasons, it has unpredictable
loadings and 72% of delays are due to
passenger behaviour.
Because of this, Line
1 was
chosen for
Paris’s latest automatic train project. It is 60
years since the Metro first tested Automatic
Train Operation (ATO). It was progressively
introduced throughout the network
between 1969 and 1979. In 1998,
Unmanned Train Operation (UTO) was
introduced on the new Line 14. The
conversion of Line 1 to UTO builds on this
experience.
Converting an existing line to UTO is a
world first and far more challenging than
building a new UTO line. These challenges
included an agreement with the workforce,
combined running of manned and
unmanned trains, fitting platform screen
doors to existing platforms, and
commissioning a new control room. (A full
explanation of Line 1’s UTO can be read in
issue 89, March 2012). By November, most
trains were unmanned with full UTO
operation planned for the year end, allowing
headways to be reduced from 105 to 85
seconds.
This UTO conversion is attracting great
interest with the Railway Division’s technical
visit to Line 1 being the 100th. As reported
elsewhere in this issue,
the Line 1 conversion
(Above) King’s
Cross escalator
room.
(Inset) King’s Cross
northern ticket
hall.
56 | the rail engineer | december 2012
(Above) Metro line
1 control room.
(Right) RER line A
control room.
light rail
has already inspired Glasgow’s
Subway, so will London be seeing
UTO soon? Although Jubilee line
trains are UTO-capable, the
answer is not for a while. Getting
workforce agreement is one of
the most difficult aspects of
conversion to UTO. Although
Paris (and Glasgow) has
achieved this, such an
agreement in London is a long
way off.
Trains grandes lignes sous
Paris
RER (Réseau Express
Régional) Line A did for Paris
in 1977 what Crossrail will do
in London 40 years later.
Today it carries just over a
million passengers per day.
This is a 20% increase over the
past ten years and a threefold
increase since the opening of its
central tunnel under Paris.
Thus, soon after opening, headway
and capacity became major concerns.
So it was that, in 1989, the SACEM
signalling system was introduced on
its central section to reduce headways
from 2.5 to 2 minutes. With SACEM,
trackside signalling is switched off and
trains are driven manually using a
permitted speed cab display with either
a green or yellow surround depending on
whether acceleration or braking is required.
The driver also has an indication of whether
braking down to 30 kph is required or
braking to a standstill. If permitted speeds
are exceeded, the emergency brake is
applied.
With the increase in traffic far exceeding
SACEM’s capacity gain, new double-deck
trains are now the solution. Until recently,
rolling stock consisted of trains carrying
Two cities in two
days
around
1800. These are now being progressively
replaced by double deck trains with a
capacity of 2600. These are 43 MI2N units
delivered since 1997 and 60 MI09 units, the
first of which was introduced in 2011.
Line A is an advanced railway, and one of the
world’s busiest. Managing its 661 trains each
day with tight headways and 50 seconds
station dwell times is a challenging task. The
70s vintage of its control room’s mosaic panels
and dot matrix LEDs show it had been doing
this for some time.
Railways are often
constrained by their history.
London tube’s heat problem
is a result of small diameter
tunnels. Headway is a
particular issue for Paris
with closely spaced stations and the traffic
generated by RER’s mainline railway under
the city.
When visiting different cities it’s difficult to
avoid comparisons. In London, St Pancras /
King’s Cross is a world class international
gateway. In Paris, the RER is 40 years ahead
of Crossrail and, for headway management,
there is much to learn from UTO/SACEM.
The Railway Division’s autumn technical
visit offered some fascinating insights. It will
be interesting to see what next autumn
brings.