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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So why is Peterborough growing so quickly?

Peterborough Cathedral. Image: Jules & Jenny/Flickr/creative commons.

The latest instalment of our series, in which we use the Centre for Cities’ data tools to crunch some of the numbers on Britain’s cities.  

The 2001 census put the population of Peterborough at 156,000. Some time before next spring, it’s projected to pass 200,000. That, for those keeping score, is an increase of about 28 per cent. Whether this makes it the fastest growing city in Britain or merely the second or the fourth – the vagueness of Britain’s boundaries means that different reports reach different conclusions – doesn’t really matter. This is a staggering rate of growth.

Oh, and since austerity kicked in, the city council has had its grant from central government cut by 80 percent.

Expansion on this scale and at this rate is the sort of thing that’d have a lot of councils in our NIMBY-ish political culture breaking out in hives; that seems to go double for Tory-run ones in Leave-voting areas. This lot, though, seem to be thriving on it. “I think the opportunity in Peterborough is fantastic,” says Dave Anderson, the city’s interim planning director. “We’re looking at growing to 235,000 by the mid-2030s.”

More striking still is that the Conservative council leader John Holdich agrees. “I’m a believer in ‘WIMBY’: what in my back yard?” he says. He’s responsible, he says, not just to his electorate, but “to our future kids, and grandkids” too – plus, at that rate of growth, a lot of incomers, too.

All this raises two questions. Why is Peterborough growing so quickly? And what can it do to prepare itself?

If you’re a little uncertain exactly where Peterborough is, don’t worry, you’re in good company. Until 1889, the “Soke of Peterborough” was an unlikely east-ward extrusion from Northamptonshire, far to its south west. Then it was a county in its own right; then part of the now-defunct Huntingdonshire. Today it’s in Cambridgeshire, with which it shares a metro mayor, the Conservative James Palmer. When I ask Holdich, who’s giving me a whistlestop tour of the city’s cathedral quarter, to explain all this, he just shrugs. “They keep moving us about.”

Sitting on the edge of the Fens, Peterborough is, officially, a part of the East of England region; but it’s just up the road from East Midlands cities including Leicester and Nottingham. I’d mentally pigeonholed it as a London-commuter town, albeit a far flung one; but when I actually looked it up, I was surprised to discover it was closer to Birmingham (70 miles) than London (75), and halfway up to Hull (81).


The more flattering interpretation of all this is that it’s on a bit of a crossroads: between capital and north, East Anglia and the Midlands. On the road network, that’s literally true – it’s where the A1 meets the A47, the main east-west road at this latitude – and railway lines extend in all directions, too.

All of which makes Peterborough a pretty nifty place to be if you’re, say, a large logistics firm.

This has clearly contributed to the city’s growth. “It has access to lots of land and cheaper labour than anywhere else in the Greater South East,” says Paul Swinney, director of policy at the Centre for Cities. “Those attributes appeal to land hungry, low-skilled business as opposed to higher-skilled more knowledge-based ones.”

That alone would point to a similar economy to a lot of northern cities – but there’s another thing driving Peterborough’s development. Despite being 70 miles from the capital, the East Coast Main Line means it’s well under an hour away by train.

In 1967, what’s more, the ancient cathedral city was designated a new town, to house London’s overspill population. The development corporation which owned the land and built the new town upon it, evolved into a development agency; today the same role is played by bodies like Opportunity Peterborough and the Peterborough Investment Partnership.

The city also offers relatively cheap housing: you can get a four-bed family home for not much over £200,000. That’s fuelled growth further as London-based workers scratch around for the increasingly tiny pool of places that are both commutable and affordable.

The housing affordability ratio shows average house prices as a multiple of average incomes. Peterborough is notably more affordable than Cambridge, London and the national average. Image: Centre for Cities data tool.

It’s made it attractive to service businesses, too. “London has probably played quite a big role in the city’s development,” says Swinney. “If you don’t want to move too far out, it’s probably one of the cheapest places to move to.”

The result of all this is that it has an unusually mixed economy. There’s light industry and logistics, in the office and warehouse parks that line the dual-carriageways (“parkways”) of the city. But there are also financial services and digital media companies moving in, bringing better paying jobs. In a country where most city economies are built on either high value services or land-hungry warehousing businesses, Peterborough has somehow managed to create a mixed economy.

Peterborough’s industrial profile: more services and less manufacturing, and more private and fewer public sector jobs, than the national average. Image: Centre for Cities.

At the moment, if people think of Peterborough at all, they’re likely to imagine a large town, rather than the fair-size regional city it’s on course to become. Its glorious 12th century cathedral – the hallmark of an ancient city, and at 44m still by far the highest spot on the horizon for miles around – is stunning. But it’s barely known to outsiders, and at least twice on my tour, the council’s communications officer proudly announces that the Telegraph named her patch as one of the best towns to live in within an hour of London, before adding, “even though we’re a city”. 

So part of the council’s current mission is to ensure that Peterborough has all the amenities people would expect from a settlement on this scale. “What the city needs to do is to adopt the mind-set of a slightly larger city,” says Anderson. Slightly smaller Swansea is developing a new music arena, of the sort Peterborough doesn’t have and needs. He frets, too, about retail spend “leaking” to Cambridge or Leicester. “Retail is now seen as a leisure activity: in the core of the city it’s important that offer is there.”

To that end, the early 1980s Queensgate shopping centre is being redeveloped, with John Lewis giving up a chunk of space to provide a new city centre cinema. (At present, the area only has road-side suburban multiplexes.) There’s major office, retail and housing development underway at North Westgate, as well as work to improve the walking route between the station and the commercial centre, in a similar manner to Coventry.

Fletton Quays. Image: Peterborough Investment Partnership.

Then there’s the city’s underused riverside. The council recently moved to new digs, in Fletton Quays, on the far bank of the River Nene from the centre. Across the river from the Embankment, the city centre’s largest green space, it’s a pretty lovely spot, of the sort where one might expect riverside pubs or restaurants with outdoor seating – but at the moment the space is largely empty. The Fletton Quays development will change all that, bringing more retail space and yes, new homes, too.

Jobs in Peterborough are unusually distributed around town: in many cities, most jobs are in the central business district. Image: Centre for Cities.

The big thing everyone agrees is missing, though, is a university. It already has the University Centre Peterborough, where degrees are provided by Anglia Ruskin University. The plan is for the site – a joint venture between ARU and Peterborough Regional College – to go its own way as an independent institution, the University of Peterborough, in autumn 2022. That should help provide the skills that the city needs to grow. A growing student population should also bring life and cash to the city centre. 

How big could Peterborough get? Could its enviable combination of good location and cheap housing and grand ambitions combine to make it the modern equivalent of Manchester or Liverpool – one of the great cities of the 21st century?

Well, probably not: “I think the optimum size for a city is probably about 250,000,” says Holdich. But that’s still a whole quarter bigger than now, and the council leader even discusses the possibility of refitting his dual-carriageway-based-city with some kind of light rail network to service that growing population. Peterborough’s not done growing yet.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.

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