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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How the pandemic is magnifying structural problems in America's housing market

Justin Sullivan/Getty Images

Long before Covid-19, the United States suffered from a housing crisis. Across the country, working class and low-income Americans struggled to pay rent, while the possibility of home ownership receded into fantasy. In hot markets, affordability became a struggle for even the middle class: In California, 41 percent of the population spends over a third of their income on housing costs. 

The coronavirus pandemic will only make these trends worse as millions are unable to work and the economy dives into a recession. Building could slow down in the medium term, as construction loans (risky bets in the best of times) become harder to come by. Unsubsidised affordable housing is often owned by small landlords, who are more likely to struggle during recessions, prompting flips to home ownership or sales to rental empires. 

New York Times reporter Conor Dougherty documented America’s longstanding housing crisis – and California’s efforts to battle it – in his book Golden Gates, which debuted just before the pandemic hit. “My sense is that right now coronavirus is magnifying a lot of things that were already happening,” Dougherty says.  


While Covid-19 adds new pressures, he says that many of the same issues we were facing still loom over the issue, from developers crowding the higher end of the market, to escalating construction costs, to stagnating wages and vulnerable service-sector jobs that leave ordinary Americans struggling to keep a roof over their heads. “That’s my larger message,” Dougherty says. “I think the structural problems continue to be a much bigger deal than the cyclical problem in housing.”

CityMetric spoke with Dougherty about how his thinking has changed since Covid-19, Donald Trump’s pro-suburban rhetoric, and the apparent exodus from San Francisco. 

I’ve really been struck by how strong the housing market seems to be despite the epic economic crisis we are facing. Costs seem to be higher everywhere. I've heard realtors talk about bidding wars like they haven't seen before in Philly, where I live. But perhaps that's just pent up demand from the big shutdowns?

What you have is an economy that has bifurcated. You have fewer middle-income jobs, more lower-income service jobs, and more higher-end jobs in software and finance. That's how our economy looks and that's a problem that is going to take the rest of our lives to solve. In the meantime, we have this housing market where one group of people have so much more money to spend than this other group. Cities reflect that. 

What's important about this bifurcation isn't just that you have gross inequality, but that these people have to live next to each other. You cannot be someone's Uber driver and telecommute. You cannot clean someone's house remotely. These lower-end service workers have to occupy the same general housing market as the super-high-end workers. 

All the pandemic has done is thrown that even more out of whack by creating a situation where one group of people is buying and expanding homes or lowering their home cost by refinancing, while another group are at income zero while trying to live in the same housing market with no demand for their services. When you see home prices booming and an eviction tsunami coming in the same newspaper, that tells you the same thing the book was trying to show you.

Does America writ large have the same housing shortage crisis as California and the Bay Area more specifically? There are other super hot markets, like New York City, Boston, or Seattle. But in Philly, or in Kansas City, is there really a lack of supply? 

There are three kinds of cities in America. There are the really out of control, fast-growing, rich cities: the Bay Area, Seattle, New York. There are declining Detroits and Clevelands, usually manufacturing-centric cities. Then there are sprawling Sun Belt cities. This book is by and large concerned with the prosperous cities. It could be Minneapolis, it could be Nashville. But the housing crisis in places like Cleveland is much more tied to poverty, as you pointed out. 

Those kinds of cities do have a different dynamic, although they still do have the same access to opportunity issues. For instance, there are parts of Detroit that are quite expensive, but they're quite expensive because that's where a lot of the investment has gone. That's where anybody with a lot of money wants to live. Then you have Sun Belt cities like Dallas and Houston, which are starting to become a lot more expensive as well. Nothing like the Bay Area, but the same forces are starting to take root there. 

I think that the Bay Area is important because throughout history, when some giant American industry has popped up, people have gone to Detroit or Houston. Now tech, for better or for worse, has become the industrial powerhouse of our time. But unlike Detroit in its time, it's very hard for people to get close to and enjoy that prosperity. There's a certain kind of city that is the future of America, it has a more intellectual economy, it's where new productive industries are growing. I think it's an outrage that all of them have these housing crises and it's considered some insane luxury to live there. 

A recent Zillow study seemed to show there hasn't been a flood of home sales in the pandemic that would signify a big urban exodus from most cities, with the glaring exception of San Francisco. Do you think that could substantially alleviate some of the cost pressure in the city proper?

On the one hand, I think this is about the general economy. If unemployment remains over 12% in San Francisco, yes, rent is going to be a lot cheaper. But is that really the reality we're all looking for? If restaurants and bars that were key to the city's cultural life remain shut, but rent is cheaper, is that what everyone wants? I bet you when this is all over, we're going to find out the tech people left at a much lower rate than others. Yes, they can all work from home, but what do you think has a bigger impact on a city: a couple of companies telling people they can work from home or the total immolation of entire industries basically overnight?

I don't want to make predictions right now, because we're in the middle of this pandemic. But if the city of San Francisco sees rents go down, well, the rent was already the most expensive in the nation. It falls 15%, 20%? How much better has that really gotten? Also, those people are going to go somewhere and unless they all move quite far away, you're still seeing these other markets picking up a lot of that slack. And those places are already overburdened. Oakland's homeless problem is considerably worse than San Francisco's. If you drive through Oakland, you will see things you did not think possible in the United States of America. 

Speaking of markets beyond San Francisco, you have a chapter about how difficult it is to build housing in the municipalities around big cities – many of which were just founded to hive off their tax revenues from low-income people.

That’s why you see Oregon, California, or the Democratic presidential candidates talking about shaking this up and devising ways to kick [zoning] up to a higher level of government. We've always done this whenever we've had a problem that seems beyond local governance. Like voting rights: you kick it to a higher body when the local body can't or won't solve it. 

But for better or for worse, this suburban thing is part of us now. We cannot just undo that. This notion of federalism and local control, those are important American concepts that can be fiddled with at the edges, but they cannot be wholesale changed. 

The first time I ever met Sonja Trauss [a leader of the Bay Area YIMBY group], she told me she wasn't super concerned about passing new laws but that the larger issue was to change the cultural perception of NIMBYism. We were living in a world where if you went to a city council meeting and complained about a multifamily development near your single-family house, you were not accosted for trying to pump up your property values or hoard land in a prosperous city. You were seen as a defender of the neighbourhood, a civically-minded person.

What is significant about YIMBYism is that the cultural tide is changing. There is this whole group of younger people who have absorbed a new cultural value, which is that more dense housing, more different kinds of people, more affordable housing, more housing options, is good. It feels like the tide is turning culturally and the movement is emblematic of that. I think that value shift will turn out to have been much more lasting than anything Scott Wiener ever does. Because the truth is, there are still going to be a bunch of local battles. Who shows up and how those places change from within probably will turn out to be more important. 

As you said, we've been seeing a lot of Democratic candidates with proposals around reforming zoning. How does Joe Biden's plan compare to the scope of the ambition in the field? 

There are two big ideas that you could pull from all the plans. First, some kind of renter's tax credit. It is obscene that we live in a country where homeowners are allowed to deduct their mortgage interest, but renters aren't. It is obscene that we live in a world where homeowners get 30-year fixed mortgages that guarantee their house payment pretty much for life and renters don't. If we think that it's a good idea to protect people from sudden shocks in their housing costs, that is as good of an idea for renters as it is for homeowners. 

I tell people that in this country, homeowners are living in the socialist hellscape of government intervention and price controls. Renters are living in the capitalist dream of variable pricing and market forces. Homeowners think they're living in this free market, but actually they're in the most regulated market – there are literally price controls propping up their market mortgages. 

Then there is Section 8 housing. Right now homeowners get access to the mortgage interest deduction. That programme is available to as many people as can use it, yet only about a quarter of the people eligible for Section 8 can get it. I think rectifying that is hugely important and a lot of the plans talked about that. 

The second big idea is using the power of the purse to incentivise people to more robustly develop their regions. You should have higher density housing in fancy school districts, near job centres, near transit. We're going to use the power of the purse to incentivise you, within the bounds of your own local rules, to do this right. Of course, that’s what Donald Trump is running against when he talks about Affirmatively Furthering Fair Housing (AFFH). 

When I was a local reporter in Philly, the city went through with that AFFH regulation despite Trump and HUD Secretary Ben Carson not being interested in enforcing it anymore. The city produced a fat report that maybe a few people read, but I don't think it changed policy. It's this phantom that Trump is running against, an ideal version of the policy that did not exist. It's also a phantom no one's heard of until Trump started tweeting about it. 

It’s been bizarre to watch. But Trump does seem to recognise that suburban politics don’t neatly fit into a red or blue construct. People who live in Texas and claim to want a free market system will turn around and erect local regulation to make sure nobody can build apartments near them. People in the Bay Area who claim to be looking for a more diverse place will use different logic, anti-developer logic, to keep apartments being built near them. 

People like that regardless of how they feel about things nationally. The bluntness with which Trump is doing it is discordant with the electorate and quixotic because people don't know what he's talking about. But the basic things he recognises – can I make voters feel like their neighbourhoods are threatened – he's onto something there. As with many things Trump, his tactics are so off-putting that people may ultimately reject them even if under the surface they agree.

You hear people on the left say the scary thing about Trump is that one day a good demagogue could come along. They're going to actually tax private equity people and they're actually going to build infrastructure. They're going to actually do a lot of popular stuff, but under a racist, nationalist banner. I think the suburban thing is a perfect example of that. There's a lot of voters even in the Bay Area who [would support that policy] in different clothing.

The world has changed completely since Golden Gates debuted just a few months ago. Has your thinking about housing issues changed as a result of the seismic disruptions we are living through?

The virus has done little more than lay itself on top of all of the problems I outline in the book. Whether we have an eviction tsunami or not, a quarter of renters were already spending more than half their income on rent. There's a chapter about overcrowded housing and how lower-income tenants are competing with each other by doubling, tripling, and quadrupling up for the scant number of affordable apartments. We now know that overcrowded housing is significantly more of a risk [for Covid-19] than, say, dense housing. If you live in a single-family home with 15 people in it, that's a lot more dangerous than 40 apartments in a four-story building.

Housing is just a proxy for inequality, it's a way of us building assets for one group at the exclusion of another. It is an expression of the general fraying of American society. I don't feel like that larger message has been affected at all, it's only been enhanced by the pandemic. With the caveat that this can all change, it just doesn't seem to me like there's some uber housing lesson we can learn from this – other than having a bunch of people crowded together is a really bad idea. 

Jake Blumgart is a staff writer at CityMetric.