Growth through innovation – Lausanne’s new driverless metro

Lausanne’s new driverless metro line – named m2 – began commercial service in October 2008. The new line has boosted the ridership of the city’s public transportation network which has increased by almost 30% since commercial service started. Costing approximately £600 million, this remarkable ‘micrometro’ has 14 passenger-friendly stations and its steep and curvy gradient strongly influenced the decision on components such as rolling stock design and station requirements.

A small public transportation company ready to innovate tl is the public transportation company of the Lausanne region along the shores of the Lake of Geneva in Western Switzerland. tl’s 1’000+ employees run a mixed metro, light-rail and bus network. During its long history, tl has been open to innovation at different stages of its development, for example:

• In 1877, with the operation of Europe’s first cable car, the Metro Lausanne-Ouchy. This hydraulically powered cable car was replaced in 1955 by a cog-wheel train which ran until 2005 when it was taken out of service to be replaced by today’s m2 driverless metro.
• In 1886, tl introduced its first tramway and operated a tramway network for passenger and goods transportation until 1964 when – in the postwar automobile euphoria – the last tramway was taken out of service.
• In 1932, tl introduced its first trolleybus and remains to this day a ‘trolleybus city’ with over 50km of trolleybus lines.
• In 1991, tl inaugurated the m1, an urban ‘tram-train’ which runs every five minutes at peak hours on a single track.
• Since 28 October 2008, tl has been operating its second urban rail line, a new metro line named m2 which is the object of this article. Since commercial service began, the Lausanne m2 metro has been widely considered a success by the population it serves and the authorities who ‘willed’ it.

‘Compact-metro’

It is a small 6km-long subway line (a ‘compactmetro’). Lausanne, with its population of 250,000, is the smallest city to date with a driverless metro. Implications are numerous on the conceptual design of the system and the organisation of its operation. They include short station distances, short trains and small train stations with limited in situ staff.

‘Mountain-metro’

It is the steepest in the world. The maximum 12% gradient slopes led to the choice of chosing vehicles with rubber tyres and associated technical features such as a ‘flat tyre’ alarm system. This ‘mountainmetro’ includes strongly inclined station platforms and platform doors. It requires unusual braking and energy recycling/ dissipation for the trains.

Accessible

The underground stations are located very near the surface, and this – combined with small stations – optimises passenger accessibility. The station architecture is very open and makes abundant use of natural light.

Train interval

The peak hour operating mode features a small carrousel synchronised within a large carrousel in order to double capacity and produce a train interval of approximately 2 minutes 50 seconds on the central section.

Unique infrastructure

The m2 infrastructure included unique structures including a metro bridge built under a remaining road bridge a century old, and the ‘recycling’ of 19th century tunnels for a modern subway.

Convincing the public

It is Switzerland’s first driverless metro. The population needed convincing of the safety and reliability of this new system. This also required working outside the usual normative framework and demonstrating system safety through a series of combined analyses and in situ testing.

Fire safety

Modern fire safety requirements can heavily influence underground public transportation projects and can significantly add to their budget. In the case of the m2, a fire risk management approach was developed which resulted in an interesting and economically reasonable ventilation system for smoke management in the tunnels.

Organisational changes

As a small public transportation company with a strong emphasis on operating a bus network, tl had to adjust its organisation for the opera – tion and maintenance of a modern metro. The procedure-based railway operation, the demanding safety standards and the driverless system with an emphasis on centralised command post operation, forced tl to revisit its professional culture.

The new line has boosted ridership

Because of geography and topography, Lausanne’s public transportation lines mostly run east to west instead of forming a ‘nice spider web’ pattern. The bus network was redesigned around m2, its new high performance backbone running along a north-south axis. The network is strengthened through the m2 which is directly connected to two thirds of tl’s bus lines and all present and planned light-rail lines. It runs through (underneath) the heart of the city and has ‘shortened’ distances between key city neighborhoods. m2 has also boosted the image of the network and of its operator.

In the three years following the introduction of the m2 and the redesigned bus network, tl’s ridership – which was stable in previous years – has increased by approximately 30%, reaching an expected 100 million passengers in 2011. With 25 million passengers in 2010, m2 has been the trigger and engine of this new growth. m2 ridership has far exceeded expectations and is increasing at an annual rate of approximately 10%.

Cost and financing

The m2 was built in four and a half years, starting in spring 2003. The 736 million Swiss Francs (approximately €600 million) cost was financed with one quarter by the Swiss Federal government and the rest by local (state and city) public funds. Remarkably the state financing was secured through a popular vote in which the citizens of the Canton de Vaud approved the proposed infrastructure with a 62% majority. This gave the project a strong legitimacy, which proved helpful in face of certain oppositions and difficulties which were later encountered.

Operation of the m2 requires approximately 70 staff (mostly operators, maintenance specialists and station attendants). Cost and revenue per passenger are in line with those of the rest of tl’s network.

A challenging infrastructure project

About half of the project budget was spent on the construction of the 6km-long infrastructure. It is 90% underground, including 2.9km of new tunnels, 2km of new cut-and-cover tunnels and 0.5km of renovated 19th century masonry construction tunnels. It also includes two bridges and 14 stations

The parallel construction of six tunnels was required to respect the tight construction schedule and to respond to the varying geological conditions. The engineers and contractors faced difficult technical and logistical challenges as these tunnels were excavated at low depth in a dense urban environment.

Although most of the m2 tunnels were excavated in relatively good sandstone, their low depth (typically 10m to 25m) presented risks and challenges. Some sections needed to be built in weak water saturated soils (sands and gravels), and required the implementation of specialised excavation techniques such as jet grouting and umbrella forepoling. In February 2005, the m2 project suffered a major construction accident when the front section of a tunnel caved in, creating a sink hole and causing extensive material damage. Massive efforts from engineers and contractors succeeded in preventing this accident from delaying construction completion.

The most visible and spectacular structure of the new m2 metro line is the Saint-Martin bridge. Because there was no place for a new bridge across the densly urbanised Flon Valley, the design engineers boldly chose to align the new bridge just below an existing 100-year-old masonry and steel road bridge. Building the new m2 bridge through the piles and abutments of the old bridge – without traffic interruption – was a technical challenge. It was also essential to ‘fit’ the new bridge to its urban and architectural setting.

A fully automatic transportation system

The key components of the transportation system – rolling stock, the driverless system, energy and track – were supplied by Alstom Transport. This includes 15 30m-long trains with a nominal passenger capacity of 222. They run on a ‘three rail’ track which guides the trains and also provides the 750 V DC current.

The trains are piloted by a driverless system with CBTC train control software. The advantages of driverless operation are high safety, frequency, reliability and flexibility (the flexibility is a welcome feature for a line which has high weekend ridership fluctuations depending on the weather or special events).

At peak hours, m2 is currently operating on a double carrousel scheme with a 2 minute 50 second train interval on the central section. In this operation mode, every second train reverses direction at stations CFF and Sallaz, thus doubling capacity between these stations. At CFF station, the pressure for faster operation has prompted the operator to reverse trains ahead of the station rather than behind the station. The passengers have adapted quickly to this which works surprisingly well.

The track layout and train control software are designed to run at a 2 minute train interval in the future. Even though the maximum nominal speed of the trains is 60km/h, the current commercial speed is only about 17km/h due to the high density of stations, the long technical times and the complex line geometry.

For historic and cost reasons, the new m2 runs in a tunnel – built for the predecessor 1877 cable car – which is too narrow to accommodate a double track. m2 therefore has to be operated with a 200m single track section south of station CFF. Even though the operator has learned to operate around this constraint, it will have to be removed in the future when the need for higher passenger capacity requires a train interval below 2 minutes.

Scaled to the small size of the agglomeration

m2 is a ‘compact-metro’ in the sense that it is scaled to the size of a small city. The line is only 6km long and the distance between the 14 stations is short: between 300 and 800m with an average below 500m (as a result, the metro does not have to be doubled up with an open surface bus line, thus freeing public space and financial resources).

The ridership of 25 million passengers a year is small, even if it is remarkable for an agglomeration with a population of only 250,000. Keeping the attractive high train frequency (between 2 and 3 minutes) made possible by fully automatic operation, the scaling down of the capacity is obtained with shorter 30m trains (only two cars compared to the usual six to eight cars). The 15 vehicle train fleet is maintained in a small garage-workshop.

Short trains also means small stations. They are located as close as possible to ground level in order to facilitate access and the use of natural light. Only two stations out of 14 have platforms deeper then 20m underground. As a result of their small size, low depth, open access and good integration in their urban environment, the stations are very accessible. This is a key factor in the attractiveness of an ‘urban elevator type’ metro such as the m2. It also reduces the investment maintenance and operation costs of mechanical station equipment such as elevators and roll-stairs.

Adapted to the topography of the city

With its steep and curvy line, m2 can also be called a ‘mountain-metro’. Rising from the Lac leman shores at 373m above sea level to 711m, it features an average slope of 6% and maximum gradients of 10-12%. The short open air sections of the line are equipped with rail heating systems in order to fight icing during harsh winter climate. The line is also curvy (minimum radius of 80m) in its central portion in order to connect key traffic generators and adapt to the hilly topography.

As a result of the line steep gradient, the stations are inclined, some of them very strongly like for the 12% inclined Station Gare CFF. This required particular attention to platform screen doors. Tests where conducted to validate the choice of doors that needed to be perpendicular to the platforms and to demonstrate their durability in repeated inclined open-close cycles.

The choice of rolling stock with rubber tyres was directly linked to the metro’s steep gradient. Tests demonstrated that the adherence of rubber tyres on steel tracks was sufficient to guarantee adequate traction and braking performance. It is interesting to note that the 60km/h maximum speed of the rolling stock is limited to 35km/h when going downhill on a 12% slope. Together with the high density of stations and long technical times, this contributes to explain the low design commercial speed of 20km/h.

The rolling stock designer and supplier had to innovate regarding the motorisation. Because of the slope, all bogies – instead of the usual two out of three – are motorised. The usual braking equipment is complemented with a magnetic brake for emergency brake and ‘parking’ function. The electrical engine braking energy is recycled in the system, but due to the high slope, rheostatic elements had to be added on the roof of the trains for the thermal dissipation of unused energy. Because the trains are short, the equipment placed under the cars had to be organised very densely.

Switzerland’s first driverless metro

Switzerland has a longstanding and extensive network of rail lines of different types, but no metro, and in particular no driverless metro. The m2 required a new approach from the overseeing authority including the pragmatic adaptation of applicable safety regulations. This is illustrated with the case of fire safety. For modern underground train and metro lines, fire safety has become a key requirement, strongly influencing design, costs and operation. The design of the operator driven smoke-control system of the m2 tunnels is innovative. It is risk-based and adapted to the configuration (tunnel length, slope and station distance). The system efficiency was demonstrated with in situ smoke tests. The beneficial impact on the fire safety of an early and strong collaborative partnership with the firefighting service is noted.

At the time commercial service began, it was also crucial to convince the population of the safety of a driverless metro. Technical features such as screen doors, extensive video surveillance and visual and audio passenger information were helpful. It was also important to show that station agents would be present, and that ‘driverless’ does not mean ‘manless’. Finally, communication efforts where geared to present the new metro as an ‘urban elevator’. After a few months of operation, the ‘driverlessness’ of the system was a not an issue for the passengers.

Doubling capacity by 2030

In summary, Lausanne’s new m2 metro line demonstrates the successful implementation of a driverless metro in a city which is much smaller then has usually been assumed to be suited for such technology. The pertinent scaling of the system to the size of the city and its adaptation to the city’s demanding topography were key factors of this success.

m2 ridership has been strong from the start and continues to grow. tl must therefore plan for the early and progressive increase of the capacity of the m2. Ultimately, and in line with UITP’s PTx2 initiative, the goal is to double capacity by 2030 in order to be able to transport 45 million passengers per year. This will happen through an increased number of passengers per train, faster commercial speed and additional trains. Finding efficient, reliable and ‘readable’ operation modes will also contribute to best adapting the available capacity to the demand. Innovation will again play a key role in answering the challenge of improving and extending a complex system while maintaining operation.

About the Author

Marc Badoux studied civil engineering at ETH in Zurich and received his doctorate degree in structural engineering from the University of Texas at Austin in 1987. He then worked with engineering companies in Switzerland and the United States before becoming an associate professor in the field of construction and risk management at the Swiss Federal Institute of technology in Lausanne (EPFL). After obtaining an MBA from IMD in 2003, he lead the construction of the m2 and since 2008, Marc has been the Deputy Director of tl. He is responsible for the management of a mixed metro, light-rail and bus network.