To RER A, or to RER C? How Paris typifies the two models for cross-city commuter train lines

RER A, not quite in action. Image: Getty.

Since World War Two, some cities have sought to extend rapid transit into their suburbs by leveraging legacy commuter rail lines. Building on prewar examples from Berlin and Tokyo, they initiated a variety of treatments to modernise their commuter rail: electrification, integrated fares, high all-day frequency, and cross-city connections.

All this turns commuter rail into an express metro line. The city that has done the most in this direction is Paris, which since the 1970s has built a network called the RER, with five lines labeled A through E.

It is the cross-city connections that are the costliest to provide, since they almost always involve new tunnels under city center. Cities can build cross-city tunnels in two ways. One approach involves high investment: the tunnels are longer and involve several stations, often in difficult-to-construct locations. The main example is the RER A, whose construction involved about 17 km of new tunnel and seven underground stations, running on an east-west axis through central Paris.

The other approach is lower-investment: tunnels are the shortest possible connecting commuter rail terminals. The main example is the RER C, whose construction involved just 1 km of new tunnel and no new stations, creating an southeast-to-southwest line on the Left Bank of Paris.

A geographically accurate map of the RER network in central Paris. RER A is in red; RER C is in yellow. Image: Wikimedia Common.

This is a spectrum rather than a binary division: RER lines B, D, and E are intermediate between the high investment that went into the RER A and the low investment into the RER C. In layout, the RER B is quite similar to the RER A, but managed to leverage a legacy line reaching within 2 km of city center.

The same division between the two approaches holds outside Paris, too. In London, Thameslink is similar to the RER C, whereas Crossrail, with its long new tunnels, is like the RER A, as is the planned Crossrail 2. Berlin's North-South Tunnel from the 1930s, creating a new axis in the city complementing the older east-west Stadtbahn, is like the RER A.


North American projects, including the SEPTA Regional Rail tunnel in Philadelphia and the ongoing Toronto RER project, are both like the RER C. The Regional Rail tunnel connected two commuter rail terminals to create a mainline the shape of an inverted L, with some lines self-intersecting. Toronto is fortunate enough not to need new tunnels at all, since all commuter lines serve Union Station, some coming from the east and some from the west.

The main benefit of the RER C style is that it is much cheaper. It involves less tunneling, and the city can choose to build fewer stations. When tunneling deep underground, the stations are the most expensive element: for example, in New York's Second Avenue Subway, built deep to avoid street disruption, the tunnels cost $415m whereas the three new stations cost $2.2bn total. The central segment of the RER A cost about 5bn francs, corresponding to about €600m per kilometer in 2016 prices; no other rail tunnel in the world has cost so much except some New York lines and Crossrail. Crossrail, the other major modern example of this type of construction, is even costlier, perhaps £750m per kilometer.

The main benefit of the RER A style is that it lets commuter rail act as an express metro line. Such tunnels do not follow the shortest path between legacy terminals: both the RER A and Crossrail were designed as express east-west lines through city center, with stations connecting to most intersecting Metro or Underground lines. And they are not just commuter rail schemes but also relief lines for the busiest metro lines, namely Metro Line 1 and the Central line. RER C-style lines do not necessarily provide this: the RER C is parallel to Metro Line 10, the least busy in Paris.

Another metro-like property of the RER A is that it has a long trunk segment providing high frequency. This is also true of the RER C, but not necessarily of other RER C-style lines elsewhere. Thameslink's shared trunk is short, just between King's Cross and Blackfriars, and SEPTA's trunk is only a few kilometers long. This happens when a short tunnel connects to many commuter rail branches.

Evidently, the RER A style leads to higher ridership: current ridership on the RER A is about 1.1m per weekday (see page 24 of this PDF); that on the RER C only 540,000. This is despite the fact that the sprawling, many-branched RER C is almost twice as long as the RER A.

The proposed New York-New Jersey Crossrail.

In North America, proposed regional rail modernisation projects fall on the RER C side. In New York, the Regional Plan Association has proposed using the planned new tunnels under the Hudson River to build a New York-New Jersey Crossrail project. The RPA is not planning on any new stations to connect to subway lines that have no connections to the existing Penn Station.

And in Chicago, the Midwest High-Speed Rail Association has proposed reactivating through-tracks at Union Station to create a Crossrail Chicago. The plan only includes one new urban station and has no transfers to the busiest L lines. In both cases, the Crossrail name does not imply service levels comparable to Crossrail: the routes are awkward, kludged together from the available commuter rail lines.

In Boston, plans for the North-South Rail Link are more mixed. This project would provide new tunnels connecting the city's two rail terminals, North Station and South Station, which are about 2 km apart. One RER A-style feature of the plan is that, in addition to these two stations, there are plans for one intermediate station, called Central Station (Boston's central business district stretches roughly from South Station to the planned new station). North and South Station together connect to three of Boston's four subway lines, and Central Station would connect to the fourth.

The proposed Boston North-South Link.

For a city planning to modernise its commuter rail network with new tunnels for through-running, there are merits to both models: evidently, Paris built the RER C and not just the RER A. However, it is a mistake to assume that short tunnels could provide the benefits of the RER A or Crossrail. In New York and Chicago, if there are plans to through-run trains, their respective transit agencies should at least consider adding stations to intersect more subway or L lines, or even the busiest bus corridors. For example, New York could open a commuter rail station at Astoria and, when the new Hudson tunnels are built, at Bergenline Avenue. Toronto is fortunate not to need tunnels, but it should consider adding infill urban stops on the planned RER to relieve the city's two main subway lines.

The biggest cities should probably plan on at least one RER A-style commuter line. London came to this conclusion when it began the Crossrail program; despite the high cost, it is now very likely to build Crossrail 2. The largest North American cities should learn from this and consider some truly metro-like commuter lines rather than just lines in the mold of the RER C.

Alon Levy blogs at Pedestrian Observations and tweets as @alon_levy.

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Pembrokeshire's innovative new eco-hamlet is great. But it should be the size of a city

The eco hamlet. Image: Western Solar.

The opening in January 2017 of an “eco-hamlet” for council house tenants in West Wales is great news. I have nothing but praise for a development which builds houses with a low carbon footprint, using locally grown wood, to make homes which are well insulated and powered by solar energy. It was also quick to build, with large sections being made in a factory and then assembled on site. And it was relatively cheap – at around £70,000 to £100,000 per building, it is certainly comparable to the costs of more conventional builds.

These houses are an inspiration to the construction industry and an aspiration for the home owner. After all, who wouldn’t like to live in a house that had yearly utility bills of £200, rather than the national average of £1,500?

So the problem is not the six wonderful solar houses at Glanrhyd, Pembrokeshire, or the lucky people who will get to live in them (and enjoy shared use of an electric car). The problem is that we’ve seen all of this before – but nothing changes. What we really need is far, far more of them.

Pentre Solar in Pembrokeshire. Image: Western Solar.

I’ve been involved in sustainable construction for nearly 25 years and seen many inspirational developments like Glanrhyd. There’s Julian Marsh’s home in Nottingham, Susan Roaf’s Oxford Ecohouse and the Hockerton Housing Project, to name but a few. The list is long.


Yet while many individuals continue to build these innovative and inspirational structures, we have a construction industry which still responds to these buildings with disdain. One executive from a large well-known house building company told me recently: “This is a new, expensive and untested technology. We just can’t risk building something so new with all the risks to the consumer and at a higher cost.”

But the situation is even worse than the disdain from the mainstream construction industry. Rather than being welcomed, the latest versions of these sustainable buildings are challenged at every turn. The initial response to the Welsh eco-hamlet plans were concerns about the materials, the technology and the design. The houses at Glanrhyd then had more than 20 planning conditions placed upon them. The CEO of Western Solar, the company behing the hamlet, freely admits that nearly half of their research budget went on solving problems they encountered along the way.

Thinking and building big

So it seems this kind of development just isn’t celebrated enough. There is a general atmosphere of mistrust from construction professionals. It is seen as too complex, too expensive, too risky. Yet there are positive reactions, too. Welsh politician Lesley Griffiths had this to say about the new houses in Glanrhyd:

This scheme ticks so many boxes. We need more houses, we need more energy efficiency, we want to help people with fuel poverty. It’s been really good to hear how they have sourced local products. It’s great they’re using local people to build the houses.

Surely we need to take the eco-technology we have and start rolling it out on a much larger scale. To do so would be a massive step in meeting the significant housing shortage (an estimated 125,000 extra new houses are needed every year). It would also address the disrepair of our current housing stock, and help refit the millions of houses in good repair but requiring improved performance in order to achieve the government’s 2050 carbon reduction target.

We must not forget that the 2050 Climate Change target is not some arbitrary political policy, but one based on the environmental challenge facing all of us. We need to play our part in slowing down the speed of climate change and adapting to the changing natural, social and economic environment.

The solar houses in Pembrokeshire are wonderful. But until we start building huge numbers of buildings with similar credentials, we are just celebrating a cottage industry rather than restructuring our urban environment for an uncertain future.The Conversation

John Grant is senior lecturer in natural and built environment at Sheffield Hallam University.

This article was originally published on The Conversation. Read the original article.