Paris and London are Europe’s largest 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.

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 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 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.

Two cities in two days

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.