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London’s cross-city line follows the RER model

13 Mar 2009

CROSS-CITY: Many enhancements have been made to RER Line A since it was completed across the centre of Paris in 1977. Now carrying more than 60 000 passengers/h on each track, it offers similarities to London’s Crossrail project, making a comparison particularly instructive.

Andrew Boagey, Business Director, Northern Europe, SystraMarc Genain, Project Director, Systra

Major construction work on London’s Crossrail project is expected to start in 2010. Running east-west across London, the scheme is identical in concept to the Réseau Express Régional routes in Paris, bringing passengers in from the suburbs to the heart of the city and continuing out to the other side. The most directly comparable route is RER Line A, one of five cross-city lines that make up the current RER network in Paris. Line A also runs on an east-west alignment, this being one of several common features that make comparison with the published design for Crossrail instructive.

Before discussing Line A in detail, it is helpful to recap on the RER concept, which is a response to the demands of an already congested, ever-growing city. Rather than stopping at main line termini and discharging commuters into already congested stations, trains head underground as they approach the city centre, remaining there until they re-surface on the opposite side, where they continue to the outer suburbs. RER lines absorb many passengers who might otherwise board congested metro lines, which can then more readily accommodate shorter city journeys without high volumes of commuters loading and unloading at each main line terminus.

Today, the growing network of RER lines serves all but three of the 20 most heavily-used stations in Paris. The five lines reach out 100 km from the city centre, and operation is shared between Paris operator RATP, which also runs the bus, tram and metro systems in the Ile-de-France metropolitian area, and the French national railway, SNCF. Agreements define the separation of responsibilities between the two organisations.

RATP operates Line A and most of Line B, with 67 stations in total, retaining its emphasis on this central city market. SNCF operates over a wider network, with 181 RER stations. It also operates services to 204 suburban stations in the greater Paris area. Despite the existence of two operators, the RER lines have a common branding.

The success of the RER can be measured in terms of its popularity and the growth that it has seen in recent years. In 2008 RER trains carried well over one billion passengers - around 700 million by SNCF and 450 million by RATP.

High capacity

The RER is seen as something special, not least because it is closely integrated with metro, suburban and inter-city services. It seems to have established an important, yet separate, role in the urban transport network. The essence of this success seems to lie in the clarity of purpose of train operations and the relationship with the investment that has been made.

Whenever RER routes have been built, planners have sought to cater for future growth. For example, the city centre tunnels and stations are constructed to generous dimensions. This has an inevitable cost, both in terms of disruption to the urban environment and in the impact on the exchequer. However, the train operators seem to acknowledge that their primary purpose is to make the best use of this financial and community investment. The consequence is a train service pattern based on station stops in the centre of the city for the minimum conceivable time with fast running from the centre right out into the suburbs.

Because headways between trains in the city centre are very tight and the station dwell time is very short, high-capacity trains must be used, with the ability to load and unload as rapidly as possible. Stations are also designed to ensure that passengers can move to and from street level or interchange with other transport modes quickly and safely.

Providing capacity to accommodate waiting passengers and giving space to those unable to board during periods of disruption becomes a significant design objective. When public expectations of train frequencies are high and passenger numbers are considerable, the consequence of even short delays in terms of station congestion can be significant. For this reason platforms have to be designed with spare capacity.

At Châtelet-Les-Halles, where Line A intersects Line B, the station has seven platform faces and handles 160 000 passengers every day, or 48 million a year.

Information

To help speed loading and unloading, passengers are given plenty of information about train services. Display boards on the platforms indicate the calling points of limited-stop services which are scheduled to keep inbound and outbound journey times to a minimum, and quirky alphanumeric train headcodes such as Z0LA and H0YE allow regular users to make sure that they are boarding the correct train.

Line A acts as a high-capacity metro in the centre of the city, with only 2 min between trains. Out in the suburbs, however, such tight headways are not so vital, not least because the trains generally run on their own dedicated tracks. Because of the critical timing on the cross-city tunnel section, this part of Line A is fitted with a separate system of cab signalling and automatic driving which is known as Sacem. This was put into service in 1989, and it can be considered as the forerunner of many communications-based train control systems in use today.

Development of Line A

Line A is the most heavily used RER line, accounting for more than 25% of all passengers in the Paris metropolitan area and carrying over a million passengers on most weekdays.

A glance at the history of the line is helpful, as today’s railway is significantly different from the line whose first section opened in 1969 from Nation to Boissy-Saint-Léger. A short section from La Défense to Etoile followed in 1970, and this was extended east and west until 1977, when both sides of Paris were connected by a central tunnel section, running beneath Les Halles and the main line terminus at Paris Lyon. The 5·5 km central section from Auber to Nation was opened by President Giscard d’Estaing on December 8 1977. Journey time between Lyon and Auber was just 6 min, which compared with 23 min by metro. At that time, single-track capacity was 50 000 passengers/h.

The line was intended to offer relief to four metro lines: Line 1 between Nation and Etoile, Line 6 between Denfert-Rochereau and Etoile, Line 4 between Dernfert-Rochereau and Châtelet, and Line 9 between Havre-Caumartin and Nation. These routes have since been joined by the driverless Line 14, which has absorbed more of the traffic moving east-west through central Paris.

A northeastern branch of Line A was progressively constructed to Noisy le Grand in 1977 and Torcy in 1980. Finally, in 1989, Line A was opened to SNCF trains offering services from the new northwestern development area at Cergy and from Poissy. The line had hitherto been exclusively operated by RATP, but it was now in use by both operators. RATP remained in charge of the operations control centre and the all-important central tunnel section.

Similarities

Line A measures 107 km from end to end, which compares with 103 km for Crossrail. It includes 25 km of tunnel, while Crossrail will have 27 km. Both routes have seven inner city stations, and there are 46 stations on both systems. Line A tunnels are generally single-track bores with a diameter of 6·4 m, which is also intended to be the diameter for the Crossrail tunnels.

Train operations will also have similar service objectives. Line A in Paris now carries more than 60 000 passengers per hour in the morning peak on each track, similar to the forecast figure for central London. Platform widths are also expected to be similar, at around 6 m.

The maximum speed of Line A rolling stock is 120 km/h, with an average commercial speed in the city centre of 49 km/h. Maximum station dwell time in the centre is 50 sec. This and other design targets have been achieved through careful matching of the rolling stock and signalling. Sacem is able to achieve 2 min headways between trains, allowing operators to provide a consistent level of service at 27 trains an hour. Without Sacem, the interval between trains would be 2½ min. Crossrail has similar aspirations, with automatic train operation an option under consideration for the central tunnel section.

Rolling stock

Line A rolling stock has evolved to meet the particular requirements of the RER. It cannot be described as either metro or suburban rolling stock by UK standards, and it has one defining characteristic: door width. Although there are three types of train in operation on Line A, typical door openings are between 22% and 24% of the side length of the stock.

The first generation MS61 was a three-car set built for operation using RATP’s 1·5 kV DC power supply. Fast acceleration was a key characteristic thanks to the 1 350 kW nominal rating of the DC traction motors. Each 73 m long set is able to carry 629 passengers, and there are four sets of double doors on each side of each car.

These trains have been through two major refurbishments, and the time is fast approaching when they will need replacing; RATP is currently looking at options.

The second generation MI84 stock has been in service for 25 years, meaning that this fleet too will need to be replaced in the near future. These four-car trains can accept 1·5 kV DC and 25 kV 50 Hz power supplies, and nominal rated output is 3 000 kW. Each set is 104 m long and accommodates 880 passengers. In peak hours three sets operate in multiple to give 12-car formations carrying up to 2 640 passengers. Again, each car has four sets of double doors per side.

In its search for more capacity, RATP examined the possibility of using double-deck stock, and the first MI2N double-deck train entered service on Line A in 1997. Another dual-voltage design, the MI2N is similar to the trains used on RER Line E. Each five-coach set has room for 1 162 passengers in a length of 112 m. Three sets of doors per car side are provided, but each doorway is wide enough to allow three people to enter or leave the train at the same time. RATP owns and operates all the rolling stock on Line A.

SNCF maintains the track in the northwestern section to Cergy and Poissy, but control and regulation of train movements is handled by RATP. This is seen as preferable to the situation on the north-south Line B where until recently drivers from the two organisations changed at Paris Nord, where there is also an electrical changeover between SNCF’s 25 kV supply and the 1·5 kV DC used by RATP. On Line A drivers change between the DC traction of the central section and the AC catenary of the SNCF line at Nanterre-Préfecture.

Control centre

A single control centre is a significant feature of Line A and all the other RER lines. Despite the mixed operations between SNCF and RATP, this is seen as essential to providing a successful service. The operations team comprises seven front-line signallers and three staff responsible for regulation. They are overseen by an information controller, and in addition there is a passenger information system operator, a station incident manager and a depot interface manager. All are housed in the same extensive operations room.