Speed vs coverage: How do metro systems decide how to space their stops?

The Paris Metro: quite close to another station, this. Image: Getty.

The Paris Metro averages a stop every 600m. The Moscow Metro averages a stop every 1.7km. Most of the world's largest systems are in between, several clustering in the 1.2-1.3 km range, including the London Underground, the Tokyo subway, and the Mexico City Metro.

But why is this? How come metro builders in some cities chose to build stations three times as far apart as in others? And what about those cities that have no metro system, but are building one, such as Tel Aviv or Sydney? What should they do?

The basic tradeoff here is between speed and coverage. Wider stop spacing means fewer locations have a metro station, but the speed between the stations is higher. The Moscow Metro averages 41 km/h, while the Paris Metro only averages about 25km/h. Other systems are intermediate: in Tokyo the average speed is about 30km/h; in London 33km/h.

There are other factors determining average speed, so that newer lines are often fast for their stop spacing. But each additional station adds about 40-60 seconds of travel time, depending on top speed, track quality, and train acceleration capabilities. The tradeoff, then, is the question: are more stations worth the extra travel time?

Each metro-building tradition answers this question differently. In cities where the metro extends deep into suburbia, stop spacing is wide; Paris built the RER as a separate system, with express stop pattern, because the Metro was too slow to effectively serve the suburbs.

Moreover, different countries make different decisions based purely on tradition. Under Parisian influence, the Montreal and Lyon Metros have short stop spacing; under Moscow's influence the metro systems in the former Communist Bloc, from Eastern Europe to China and North Korea, usually average more than 1.5 km between stations. With neither influence, cities in developing countries that build new metros, such as in South Asia, seem to use the same stop spacing as London or Tokyo.

But there is more to the stop spacing decision than the speed versus coverage tradeoff. Large cities, which expect to build many metro lines, need to plan how those lines will intersect in their cores. The San Francisco urbanist Brian Stokle wrote about the related subject of line spacing: how cities space parallel metro lines in their central business districts. Using American examples, Stokle argues that the typical space for parallel lines is 500-700 meters; this also appears to be the average in Paris and in central London.

The upshot is that if two lines are parallel, spaced about half a kilometer apart, then a line that intersects them orthogonally had better have two stops half a kilometer apart, for transfers. For example, in the diagram below the red and blue lines are roughly parallel, and the black line is orthogonal to them.

This looks familiar. Image: author provided.

Metro planners aim to provide a transfer station at the intersection of every pair of lines. In practice, because most metro systems have denser line spacing than stop spacing, this is not always feasible. Metro systems that feed geographically small central business districts, such as central London or central Tokyo, end up with multiple missed connections; New York, where the subway was built by three separate companies, has more than twenty missed connections. But usually, there is only a small handful of missed connections, often just one or two.

A separate question is that of express lines. In New York, five of the nine subway trunk lines have four tracks, with local and express trains; in Seoul, Line 1 has four tracks as well. Thanks to the express lines, New York maintains very narrow stop spacing on the local lines.


But a more common situation is one in which every metro line has two tracks, with all trains making all stops, on which some lines are more express than others. In Paris, the RER A was built as an express version of Metro Line 1, and, decades later, Metro Line 14 was built with longer stop spacing as well, to relieve the central segment of the RER A.

This situation leads to missed connections. The RER A tries to make connections when it can, but still crosses a few lines without a transfer, or else it would be hardly any faster than Line 1.

London's equivalent, Crossrail, does the same: it misses some connections to north-south lines, because if it didn't, it wouldn't be faster than the Central line, simply because line spacing in Central London is so dense. Within the Paris Metro, excluding the RER, there are three missed connections, two involving Line 14; an under-construction extension of Line 14 misses yet another connection. In Asia, several cities, including Hong Kong, Beijing, and Delhi have express lines to the airport, with missed connections in every case.

But it's easier to build networks with long stop spacing in newer cities, purely because of how their business districts are laid out. In old industrialised cities like London, Paris, New York, and even Tokyo, there is a dominant CBD, a few square kilometers in area, and most metro lines enter it. In all of these cities, the CBDs for the most part predate the metro system.

In newer cities in developing countries, the CBDs look different, with multiple centers, sometimes purpose-built. This leads to longer line spacing, matching the wide stop spacing. On same-scale maps of their networks, Paris, London, and Tokyo all look like hard-to-follow blobs in their centers, whereas Chinese cities, especially Beijing, still look clear. In Beijing, the only missed connection today involves the airport express line.

The most ideal metro network looks radial, with a circular line or two. Every pair of radial lines should intersect, once, with a transfer station, and every radial should intersect every circle twice, again with transfers. Ideally interchange stations should only involve two lines at a time, to avoid clogging the most popular locations. The diagram above is a good example of a coherent network with three lines. Unfortunately, the interaction of line spacing and stop spacing makes the ideal network difficult to construct. It's also unlikely that the street network is perfectly aligned for this; for example, cities with street grids, like Beijing or Philadelphia, can't easily build lines diagonally to the grid.

 

The ideal network? At least, if you ignore the chaos of that central station. Image: CityMetric.

This means that the only way to guarantee easy connections between metro lines in most large cities is to build very short stop spacing, as in Paris. Unfortunately, this imposes a sharp limit on train speed - and it's precisely the largest cities that have the most need for speed, since their suburbs usually stretch farther out of city center than those of smaller cities.

Metro construction is full of compromises. Cities that are building new systems, especially in the developed world, are likely to have so much sprawl, from decades of growing without a metro, that they need long stop spacing to serve the suburbs effectively. But they also are likely to have an organic central business district with many close-in dense neighborhoods, which would benefit from short stop spacing; they also have everywhere-to-everywhere commutes, as all modern cities do, which makes good interchanges between lines a must. Something has to give, and each city needs to figure out how, in its particular situation, to choose the optimal point in the speed-coverage tradeoff.

 
 
 
 

Here’s how Copenhagen puts cyclists at the top of the social hierarchy

A cyclist in Copenhagen, obviously. Image: Red Bull/Getty.

Have you ever wondered why Britain is not a nation of cyclists? Why we prefer to sit in traffic as our Dutch and Danish neighbours speed through the city on bikes?

Forget about hills, rain, and urban sprawl: the real reason we aren’t cycling is much closer to home. It is not just lack of infrastructure, or lack of fitness, the reason that 66 per cent of Brits cycle less than once a year, is because of status.

An obsession with social status is hard-wired into our brains. As we have built a society that relies on cars, the bicycle has slipped to the periphery, and gone from being regarded as a sensible mode of transport, to a deviant fringe-dwellers choice.

Even though cycling to work has been shown to be one of the most effective things an individual can do to improve health and longevity, researcher David Horton thinks that there are a set of collective anxieties that are stopping us getting in the saddle. These include not just an unwillingness to be made vulnerable, but fear of being thought of as poor.

A quick look over the North Sea shows that there is an alternative. Danish culture has elevated cycling to the point of reverence, and the social status of cyclists has followed. As we have busied ourselves building infrastructure that testifies to the dominance of the car, Denmark has been creating magnificent architectural features, aimed specifically at bike users. The Cycle Snake, or Cykelslangen, literally suspends the cyclist above the city, metaphorically elevating the cyclist and creating a sense of ceremony.

In doing so, they are subtly persuading people of all backgrounds to see past their prejudices or fears and take it up as the clearly better choice. This means there are more women cycling, more older people cycling, and more ethnic minorities cycling. The activity is less dominated by comfortably middle class white males: there are cyclists from every side of the community.  

The Cykelslangen, under construction in 2014. Image: Ursula Bach and Dissing+Weitling architecture.

Despite abstract motivations like getting ripped and conquering global warming, it is only when the bike path becomes the obviously better choice that people will start to cycle. It can take years of traffic jams before people try an alternative, but if you make motorists jealous of cyclists, then the tables can quickly turn.

Another way that Copenhagen has done this is by taking privileges normally afforded only to the motorcar, and given them to the bike. The city has ensured that cycle routes do not include blind corners or dark tunnels, and that they form a complete, coherent network, and a steadily flowing system – one that allows cyclists to maintain a reasonable pace, and minimises the amount of times you have to put your foot down.

The ‘Green Wave’, for example, is a co-ordinated traffic light system on some of the main thoroughfares of the capital that helps minimise the amount of cycle congestion during peak times. It maintains a steady flow of cycle traffic, so that there is no need to stop at any point.


Small measures of prioritisation like this one increase the sense of safety and consideration that cyclists experience, making it natural for the citizens of a city to act in their own self-interest and get on their bike.

As well as redefining the streets around the bicycle, the Copenhagen Cycle Chic blog positively fetishises cyclists. The tagline “dress for your destination, not your journey” depicts the social fashion life of the cycle lane as a “never ending flow of happy people heading from A to B”. Its writers are  literally making cycling sexy, dispelling the idea that going anywhere by bike is odd, and helping the world to see that the bicycle is actually the ultimate fashion accessory.

So unlike in London, where cycling is still a predominantly male pursuit, Copenhagen sees a more even split between men and women. Not just because they feel safer on the roads, but because culturally they are comfortable with their appearance as part of a highly visible group.

So while our low level of cycling is partly due to our physical infrastructure, it is also due to our cultural attitudes. The mental roadblocks people have towards cycling can be overcome by infrastructure that is not only safe, but also brings old-fashioned notions of dignity and grace into the daily commute.

Of course, office shower facilities might stop cyclists being ostracised, too.