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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Where actually is South London?

TFW Stephen Bush tells you that Chelsea is a South London team. Image: Getty.

To the casual observer, this may not seem like a particularly contentious question: isn’t it just everything ‘under’ the Thames when you look at the map? But despite this, some people will insist that places like Fulham, clearly north of the river, are in South London. Why?

Here are nine ways of defining South London.

The Thames

Image: Google Maps/CityMetric.

It’s a curvy river, the Thames. Hampton Court Palace, which is on the north bank of the river, is miles south of the London Eye, on the south bank. If the river forms a hard border between North and South Londons, then logically sometimes North London is going to be south of South London, which is, to be fair, confusing. But how else could we do it?

Latitude

You could just draw a horizontal line across a central point (say, Charing Cross, where the road distances are measured from). While this solves the London Eye/Hampton Court problem, this puts Thamesmead in North London, and Shepherd’s Bush in South London, which doesn’t seem right either.

Image: Google Maps/CityMetric.

And if you tried to use longitude to define West and East London on top of this, nothing would ever make sense ever again.

The Post Office

Image: Wikimedia Commons.

Some people give the Post Office the deciding vote, arguing that North and South London are defined by their postcodes. This does have some advantages, such as removing many contentious areas from the debate because they’re either in the West, East or Central postcode divisions, or ignoring Croydon.

But six of the SW postcodes are north of the river Thames, so we’re back to saying places like Fulham and Chelsea are in south London. Which is apparently fine with some people, but are we also going to concede that Big Ben and Buckingham Palace are South London landmarks?

Taken to the extreme this argument denies that South London exists at all. The South postcode region was abolished in 1868, to be merged into the SE and SW regions. The S postcode area is now Sheffield. So is Sheffield in South London, postcode truthers? Is that what you want?

Transport for London

Image: TfL.

At first glance TfL might not appear to have anything to add to the debate. The transport zones are about distance from the centre rather than compass point. And the Northern Line runs all the way through both North and South London, so maybe they’re just confused about the entire concept of directions.

 

Image: TfL.

But their website does provide bus maps that divide the city into 5 regions: North East, South East, South West, North West and the Centre. Although this unusual approach is roughly speaking achieved by drawing lines across and down the middle, then a box around the central London, there are some inconsistencies. Parts of Fulham are called for the South West region, yet the whole of the Isle of Dogs is now in North East London? Sick. It’s sick.

The Boundary Commission

One group of people who ought to know a thing or two about boundaries is the Boundary Commission for England. When coming up with proposals for reforming parliamentary constituencies in 2011, it first had to define ‘sub-regions’ for London.

Initially it suggested three – South, North East, and a combined North, West and Central region, which included Richmond (controversial!) – before merging the latter two into ‘North’ and shifting Richmond back to the South.

In the most recent proposal the regions have reverted to North Thames and South Thames (splitting Richmond), landing us right back where we started. Thanks a bunch, boundary commission.

The London Plan

Image: Greater London Authority.

What does the Mayor of London have to say? His office issues a London Plan, which divides London into five parts. Currently ‘South’ includes only Bromley, Croydon, Kingston upon Thames, Merton, Sutton, and Wandsworth, while the ‘North’ consists of just Barnet, Enfield, and Haringey. Everywhere else is divvied into East, South or Central.

While this minimalist approach does have the appeal of satisfying no-one, given the scheme has been completely revised twice since 2004 it does carry the risk of seismic upheaval. What if Sadiq gets drunk on power and declares that Islington is in East London? What then?

Wikipedia

 

Image: Wikimedia Commons/CityMetric.

The coordinates listed on the South London article lead to Brockwell Park near Herne Hill, while the coordinates on the North London article lead to a garden centre near Redbridge. I don’t know what this means, so I tried to ring the garden centre to see if they had any advice on the matter. It was closed.

Pevsner Guides

Image: Wikimedia Commons/CityMetric.

Art historian Sir Nikolaus Pevsner might seem an unlikely source of help at this juncture, but we’ve tried everything else. And the series of architectural guides that he edited, The Buildings of England, originally included 2 volumes for London: “The Cities of London and Westminster”, and “everything else”. Which is useless.

But as his successors have revised his work, London has expanded to fill 6 volumes: North, North West, East, The City, Westminster, and South. South, quite sensibly, includes every borough south of the Thames, and any borough that is partly south of the Thames (i.e. Richmond). And as a bonus: West London no longer exists.

McDonald’s

I rang a McDonald’s in Fulham and asked if they were in South London. They said no.

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