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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What’s in the government’s new rail strategy?

A train in the snow at Gidea Park station, east London, 2003. Image: Getty.

The UK government has published its new Strategic Vision for Rail, setting out policy on what the rail network should look like and how it is to be managed. 

The most eye-catching part of the announcement concerns plans to add new lines to the network. Citing the Campaign for Better Transport’s Expanding the Railways report, the vision highlights the role that new and reopened rail lines could play in expanding labour markets, supporting housing growth, tackling road congestion and other many other benefits.

Everyone loves a good reopening project and this ‘Beeching in reverse’ was eagerly seized on by the media. Strong, long-standing reopening campaigns like Ashington, Blyth and Tyne, Wisbech and Okehampton were name checked and will hopefully be among the first to benefit from the change in policy. 

We’ve long called for this change and are happy to welcome it. The trouble is, on its own this doesn’t get us very much further forward. The main things that stop even good schemes reaching fruition are still currently in place. Over-reliance on hard-pushed local authorities to shoulder risk in initial project development; lack of central government funding; and the labyrinthine, inflexible and extortionately expensive planning process all still need reform. That may be coming and we will be campaigning for another announcement – the Rail Upgrade Plan – to tackle those problems head-on. 

Reopenings were the most passenger-friendly part of the Vision announcement. But while sepia images of long closed rail lines were filling the news, the more significant element of the Strategic Vision actually concerns franchising reform – and here passenger input continues to be notable mainly by its absence. 

Whatever you think of franchising, it is clear the existing model faces major risks which will be worsened if there is a fall in passenger numbers or a slowdown in the wider economy. Our thought leadership programme recently set out new thinking involving different franchise models operating in different areas of the country.

The East-West Link: one of the proposed reopenings. Image: National Rail.

Positively, it seems we are heading in this direction. In operational terms, Chris Grayling’s long-held ambition for integrated management of tracks and trains became clearer with plans for much closer working between Network Rail and train operators. To a degree, the proof of the pudding will in the eating. Will the new arrangements mean fewer delays and better targeted investment? These things most certainly benefit passengers, but they need to be achieved by giving people a direct input into decisions that their fares increasingly pay for. 

The government also announced a consultation on splitting the Great Western franchise into two smaller and more manageable units, but the biggest test of the new set-up is likely to be with the East Coast franchise. Alongside the announcement of the Strategic Vision came confirmation that the current East Coast franchise is being cut short.

Rumours have been circulating for some time that East Coast was in trouble again after 2009’s contract default. The current franchise will now end in 2020 and be replaced with public-private affair involving Network Rail.


This new management model is an ideal opportunity to give passengers and communities more involvement in the railway. We will be pushing for these groups to be given a direct say in service and investment decisions, and not just through a one-off paper consultation.

Elsewhere in the Strategic Vision, there are warm words and repeated commitments to things that do matter to passenger. Ticketing reform, compensation, a new rail ombudsman, investment in improved disabled access and much else. This is all welcome and important, but is overshadowed by the problems facing franchising.

Stability and efficiency are vital – but so too is a model which offers deeper involvement and influence for passengers. With the building blocks of change now in place, the challenge for both the government and rail industry is to deliver such a vision. 

Andrew Allen is research & consultancy coordinator of the Campaign for Better Transport. This article was originally published on the campaign’s blog.

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