How to build a lot more metro systems for a lot less money

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In the nineteenth century, the societies of Europe and North America were profoundly transformed by the vast railway networks they built. When these railway networks entered cities, however, they faced a crucial problem: they had to stop. Rather than carrying on through the city, it was common for them to terminate on its edge.

In part, this was due to the high cost of acquiring land in urban areas. It was also a technological problem: the tunneling technologies that would enable railways to run into the centre underground without destroying everything in their path had not yet been invented. Finally, the problem was sometimes regulatory as well: in cities such as London railways were prohibited from penetrating too deep into the urban area.

The result was that nineteenth century railways often terminated roughly wherever the city limits were when they were built. Some Victorian urban networks, like those of London and Paris, thus resemble a vast hubless wheel whose spokes do not quite join one another in the middle. In other cases, the lines circled round the city and then all entered it at the same point, terminating together in one huge station. This model was common in Germany, so that stations of this sort are still sometimes known by the German name Hauptbahnhof (literally: main station).

At the end of the nineteenth century, electrification and improvements in tunneling technology led to the emergence of a new kind of railway: the modern metro. Metros were a huge advance in three ways. First, they could go anywhere in the city. Second, metro lines could easily interconnect with one other, meaning that passengers could use the network to travel swiftly from any part of the city to any other part of the city, rather than merely going from a suburb to the edge of the center. Third, the lines were not bottlenecked by the capacity of a central terminus.

Inner-city termini like London Waterloo and the Gare du Nord in Paris have always handled a complex range of intercity and suburban trains, so delays on any one service can easily propagate over to others. To stop every small delay from generating a huge chain of further delays, tracks and platforms have to be used far below their theoretical maximum capacity: the system can only operate smoothly by preserving a great deal of redundancy. Trains therefore wait around at the terminus for longer than strictly necessary, to recover from delays.

This, in turn, means that termini have to be massive, and in the age of steam, this was compounded by needing to have room to turn around and store steam locomotives and carriages. Today, the Gare du Nord has 28 tracks above ground, and Waterloo has 24.

The giant Gare du Nord (right) and the Gare de l’Est in Paris.

As demand for railway services grew, these termini filled up. But expanding central termini is rarely straightforward: they are typically surrounded by expensive land containing dense urban fabric which would have to be demolished. Furthermore, they are often located on viaducts or in a trench, which makes their expansion technically difficult. Over time, terminus capacity thus generally became the binding constraint on the number of trains that could be run in and out of the urban core, limiting the frequency of both the suburban trains and intercity services.

Metros, by contrast, could get away with much smaller termini. A typical metro runs a very simple service pattern: every train stops at every station, with few branch lines, and shares no track with any other services, so delays are much less likely. A metro train can easily turn around in well under five minutes, so its terminus only requires two or three platforms.

In the first decades of the twentieth century, metro lines were built in cities across Europe and North America like Paris, Tokyo, London, Barcelona, and New York. In all of these cities, however, metro lines were built to supplement the Victorian legacy networks, rather than to replace them. As a result, the legacy networks are still there today.

Since building tunneled metro lines is so expensive, these legacy networks are often more extensive than modern metros. The map on the above is London’s metro network (and even this, as we will see, incorporates some bits of legacy lines). The map below shows London’s whole railway network. Nearly all of the additional lines are Victorian: the pre-metro legacy system is actually far greater than the modern metro.

London is not an anomaly. In Boston, Philadelphia and Chicago, the suburban railway network is much bigger than the metro, and the same is true in Paris, Tokyo and Berlin. A small number of expensive modern metro lines operate alongside vast Victorian networks, a legacy from the golden age of railways. In Britain, nearly all cities have a Victorian legacy network, but only three – London, Glasgow and Newcastle – have something that is unambiguously a metro.

One of the Holy Grails of transport policy has thus been a way to turn these legacy lines into something like a modern metro system. The solution developed by many transit authorities is known as through running. This means taking suburban lines on opposite sides of the city, and joining them up by running trains through the city center, usually in a tunnel. This tunnel does not necessarily have to be very long: in some cities, only a handful of kilometers is needed, because the rest of the infrastructure (the legacy lines that are joined together by the tunnel) is already there. For the price of a comparatively small section of tunnel, a large number of suburbs can get metro-like service directly into the city center.

Through running has convergently evolved in many places. This article looks at two of them, Munich and London. Munich is distinctive in having used through running to create what is probably the best transit network on earth, relative to the size of the city. London is distinctive in the sheer size of its legacy network, due to its enormous size in the nineteenth century. This means that through running has offered it opportunities of unique scale and complexity.

For countries with extensive Victorian legacy networks, through running is one of the most important themes in modern transport policy. Across the world, many cities puzzle over how they can pay for the vast costs of developing an all-new metro system. But if they can get through running right they don’t necessarily have to. Often 90 percent of their modern rail network is already there and has been for 150 years. The stories of Munich and London show how they might fill in the remaining ten percent to create world-leading transit systems at a fraction of the cost.

A terminological note. In the language of railway engineers, the Victorian legacy networks we are discussing are generally called ‘suburban railways’. This is confusing, because metros are also railways and also run in suburbs, and also because the Victorian systems in question are often the suburban sections of intercity lines. But we bow to convention, and in what follows the surface-level Victorian terminating lines are called ‘suburban railways’ and the underground networks are called ‘metros’.

Through running in Munich

Munich has a good claim to the best rapid-transit system of any medium-sized city in the world. Within ten kilometers of the center of Munich, there are 1.6 million people, who are served by 284 stations and 194 tram stops, all of which receive a fast, frequent service.

Munich has two different railway systems. The U-Bahn (short for ‘underground railway’ in German) is a conventional metro system, which serves only the urban area. But there is also the S-Bahn, which is a network of through-running trains that connect the city to outlying towns up to 40 kilometers away as the crow flies.

Before its metro system was built in the 1960s, Munich had two networks of commuter trains. One network radiated out of the Hauptbahnhof, the city’s main station, which is on the western edge of the city center. Another radiated out of Ostbahnhof, the eastern station, which is much further away from the center. For the reasons described above, neither reached the heart of the city. There was (and still is) an above-ground connection between the two stations, but it is quite a detour, with trains taking about ten minutes to travel 3.5 kilometers as the crow flies. It loops round the city center to the south, and much of its capacity is taken up by long-distance trains traveling to south-eastern Bavaria and Austria.

According to this 1893 map, the connection between Hauptbahnhof and Ostbahnhof was not used by suburban trains at all.

As mentioned above, this model of ‘spokes without a hub’ is common. In France, Britain, and the United States, the railways were initially built by competing companies that saw each other as rivals, and had little interest in sharing stations. New York City ended up with Pennsylvania Station, operated by the Pennsylvania Railroad, and Grand Central Terminal, operated by the New York Central Railroad. Paris had eight termini at its peak. London has had as many as fifteen, depending on how they are counted.

Even where railways were more centrally planned (including Munich), linking separate networks together was challenging. In Germany, Britain, America, and France, the period of explosive growth of railways mainly took place in the mid-to-late nineteenth century. In this period, tunneling technologies were still in their infancy. The only way railways could run tracks underground was by digging an enormous trench, laying the tracks in it, and then covering it over, a method called ‘cut and cover’. In urban areas, this was expensive and inconvenient: unless the line could be dug underneath a wide street, all the buildings above the future underground line had to be demolished to clear the way for the trench. The other option, which was equally disruptive and expensive, was to build large viaducts through the city center. Berlin did this in 1882 because it was essential for military maneuvers between the eastern and western parts of Germany, but Berlin was the exception rather than the rule.

By the 1920s, the shortcomings of the system were becoming increasingly obvious. The population of Munich increased sevenfold between 1850 and 1930, with most of the growth in newly built suburbs. But the capacity of the suburban network could not be easily increased to meet rising demand. For the reasons explained above, the two central termini were the key constraints on capacity. There was also continued discontent at the fact that suburban services did not reach the city center, a fact that had been made more obvious by the development of trams that could do so.

On the other hand, there were fewer capacity constraints in the termini at the suburban end, because they usually only handled one type of service (i.e. just a single suburban service, not multiple suburban and intercity ones). This meant they could handle more trains per hour without major risk of generating chains of delays. If they did face capacity constraints, it was normally easier to solve them through expanding termini, since suburban termini are surrounded by less development, and land is cheaper.

Geltendorf station, the terminus of Munich S-Bahn route S4. The station is 40 kilometers as the crow flies from the Marienplatz, the centre of Munich.

The obvious solution is through running: for the cost of a tunnel, both termini can be in the outer suburbs, where space is less scarce, and passengers can be taken directly to the city center into the bargain. This was well understood at the time, and Munich therefore began building an S-Bahn in the interwar period. However, the project was abandoned at the outbreak of the Second World War, and the desolated city was in no position to resume it when the war ended.

The headquarters of the Bavarian State Government in ruins on 1 December 1958, over 13 years after the end of the War.

In spite of the scale of the destruction, the 1950s were also the time of West Germany’s Wirtschaftswunder, or economic miracle: West Germany’s GDP per capita recovered to its prewar level after only ten years, and the country built half a million housing units annually in the 1950s. In an environment of rapid reconstruction, the prewar transport networks in cities like Munich became overloaded. Munich’s population grew to a million in 1957 from its nadir of 550,000 in 1945, and in 1961 114,000 commuters were using the suburban trains every day.

The response to this problem was the Munich S-Bahn, which linked together 12 pre-existing suburban branch lines with a 4.3-kilometer-long tunnel. The first concrete postwar plans for the tunnel were put together in the late 1950s. In 1963, the tunnel was approved by Munich’s city council, and following negotiations about funding it began construction in 1966. In the same year, Munich was awarded the 1972 Olympics, putting a hard deadline on completion of the S-Bahn, which ultimately opened a few months before the Games began.

Including related works to the surrounding lines, it ultimately cost 900 million Deutschmarks, or $2.8 billion in 2023 US dollars. This relatively small investment enabled a network of through-running trains that is today a hundred times as long as the tunnel, because the branch lines had already been built.

The most obvious benefit of the S-Bahn was that it made it easy to get to the center. Previously, somebody travelling from the eastern suburb of Erding had to get a suburban train to Ostbahnhof, get off, go to the station forecourt, and finish their journey with a 15-minute tram ride. Today, the S-Bahn whisks them directly to the heart of the city, and the S-Bahn tunnel has six central stations, which means that different parts of the center are accessible without changing trains.

Just as importantly, the S-Bahn tunnel was not planned as an isolated project, but as one component of a wider public transport network. Munich’s 1963 city development plan envisaged integrating the S-Bahn into a single network with the U-Bahn metro system. There would be five trunk lines under the center, four of which would be operated as part of the U-Bahn, and one of which was the S-Bahn tunnel.

Munich’s transport network as planned in 1963.

Today’s S-Bahn and U-Bahn network is similar to what was planned in 1963, although only three of the four U-Bahn trunk lines were built, and the circular line never came to fruition. It is a single network: the S-Bahn tunnel intersects with each U-Bahn line, and the interchanges were designed coherently: with the exception of Hauptbahnhof, none of the interchange stations has more than two lines intersecting, which prevents any station from being overloaded. The fares are also integrated between the two systems, so that passengers are not penalised for changing trains. The S-Bahn tunnel would have been useful in itself, but its integration with the U-Bahn has a ‘multiplier’ effect: with one change of train to the U-Bahn, an S-Bahn passenger can get nearly anywhere in the city.

This principle of ‘one network, two systems’ enables Munich to manage the trade-off between station spacing and speed, so that both the dense urban core and the suburbs can be served by rapid transit. Other cities try to achieve the same result by running both express trains, and trains that stop at every station, on the same lines, but this is difficult to do effectively, for the obvious reason that the fast trains tend to get bottlenecked behind the stopping ones.

The S-Bahn has also relieved the main station. Today, Munich Hauptbahnhof has 32 terminal tracks above ground which handle about 30 departures per hour in the evening peak, because nearly all of the suburban trains run into the S-Bahn tunnel. One train per track per hour is very low utilization, which means there is plenty of room to make sure delays do not cascade across the network, expand the service in future, or possibly to rationalize the station by selling off part of the track space for development.

But beyond the better connections and the relief provided to the main station, the most important benefit of the Munich S-Bahn has been its frequency. The trunk is able to handle 32 trains per hour in each direction because the branches start in one outlying suburban town, go through the trunk, and then terminate in another suburban town. (Munich has, since December 2024, started temporarily running one branch into Hauptbahnhof due to reliability issues in the trunk.) This gives it a capacity of up to 48,960 passengers per hour in each direction.

The Munich S-Bahn accounts for 840,000 journeys each workday, serving an area with a population of about 2.7 million. It carries two thirds of all railway passengers in Bavaria, a state with a population of 13.4 million. This is impressive in itself, but the Munich S-Bahn also performs better than some other through-running systems: the Paris RER, a structurally similar system in a much bigger city, serves four times as many people but only carries three times as many passengers per day. The S-Bahn tunnel, which was originally only designed for 250,000 passengers per day, has been so successful that Munich is building a new one, to move every branch from three trains per hour to four, and to create the capacity for half-hourly express services.

Many cities, especially in the German-speaking world, have tackled their problems in a similar way. Berlin, Hamburg, Stuttgart, Frankfurt, Leipzig, Vienna, and Zurich all have networks very similar to the Munich S-Bahn, using tunnels to link up lines on opposite sides of the city. Not all S-Bahns require an expensive tunnel: some cities like Cologne, Nuremberg, and Hanover do not have a terminus, so they can simply run their trains through the main station. The S-Bahn model has also been influential on cities in neighbouring countries, such as Copenhagen, Stockholm, Prague, Brussels, and Milan.

Karlsruhe, a small city in the south-west of Germany near the French border, developed an interesting variation on through running in the 1990s: the tram-train S-Bahn. A ‘train’ from the big town of Pforzheim starts off running on ordinary rails, then through runs on the city streets of Karlsruhe as a tram, before becoming a train again on the other side of the city. Although the tram portion is slow, the city is small enough that this does not have a large effect on journey times. The ‘Karlsruhe model’ has been emulated around the world, including in Sheffield in the United Kingdom.

In all of these cities, the principle is the same: to enable all of the suburban railway lines to through run onto a trunk that goes through the city center, whether that trunk be a tunnel, platforms at the main station, or occasionally a tram network.

Through running in London

Through running has convergently evolved in several different places. One of these was Germany. Another was London.

In the nineteenth century, London was the world’s largest city, and it had an enormous network of suburban railways. These were originally built by competing, private companies, which were set up in the mid-nineteenth century to connect the capital with other major cities like Birmingham, Bristol, and Brighton. Each company built its own London terminus almost always on the edge of the urban area. The theoretical opportunity for through running in London was thus gigantic, uniting the enormous and disorganized system of suburban railways.

Paddington Station, the terminus of the line from Bristol, is shown on the edge of the urban area in this 1853 map.

The problem with London’s suburban railway system has been obvious from a start. As soon as underground railways became possible, companies began designing networks to connect the various termini together, beginning with what later became the Metropolitan and District lines of the London Underground. Their aim was to allow commuters to move between the various disconnected ‘spokes’ of the suburban ‘wheel’. This was not, however, through running: passengers would need to change trains at a terminus like King’s Cross to get to the early Underground lines. The suburban lines were not directly linked together.

The Victorians managed only one true example of through running, the Snow Hill Tunnel. This went south from Farringdon to a station called Ludgate Hill, which enabled the lines north and south of the Thames to be connected. London’s first crossrail can thus be dated to 1 August 1866, when the first trains used this new connection to run from Herne Hill, in the south of London, to Barnet, in the north of London. Although the service was initially fairly successful, the slow, infrequent, steam-operated suburban service was outcompeted by electric trams after the Kingsway tunnel allowed them to cross the river, and closed to passengers in 1916.

The Snow Hill tunnel briefly enabled an early form of the through running in London. It now forms part of the Thameslink line.

This success of the Snow Hill Tunnel was not repeated. One problem was that through running would have involved railway companies letting one another’s trains run on their tracks, which they were often unwilling to do. Another was that through running would require more cut-and-cover tunnels to be built, which meant digging a huge trench, laying the track in it, and covering it over. Cut and cover requires the total destruction of everything in the way of the trench, which makes it phenomenally expensive, unless it follows the line of a wide street. Some cities, like New York and Paris, had lots of wide streets for this purpose, but central London has only one, Euston Road, which already had the Metropolitan Line running underneath it.

At the end of the nineteenth century, advances in tunneling technology meant a new generation of underground lines could be built. These ‘deep level’ lines, powered by electricity, ran far beneath the surface of the earth and were bored rather than excavated, so they no longer required destructive trenches to be cut through the urban fabric. This did not, however, solve London’s through-running problem. The suburban lines remained operated by steam, so none was suitable for through running without expensive investment in electrification.

Through running began to get underway again in the 1930s, after London’s railway services were nationalized and schemes began to be developed to coordinate them more effectively. As part of its New Works Program, the London Passenger Transport Board joined a short Edwardian underground line with two suburban railway lines on either side, resulting in what we now know as the Central Line. The suburban lines were electrified so that their trains could run through the underground line, and then out into the suburban line at the other end. A total of 14 kilometers of tunnel were built to join the lines together.

By the 1940s, there was high enthusiasm for further through-running schemes. In 1943, planners prepared the County of London Plan for rebuilding London after the Second World War, which included grand designs to through run nearly all of London’s suburban railways with a series of tunnels. The Plan’s rail proposals were mainly downstream of its plans for improving the South Bank of the River Thames, an area criss-crossed by three huge railway viaducts which, the planners judged, impeded rational planning of the area. The Plan therefore suggested removing the stations and their attached viaducts, and building a series of tunnels which would enable through running of nearly all traffic.

The 1943 plan to through run London’s suburban railways.

However, these schemes came to nothing. The British state was virtually bankrupted by the Second World War, with government debt rising to 270 percent of GDP, and struggled to initiate major infrastructure projects in its aftermath. Resources were channeled into finishing the pre-war extensions, with the Central Line Extension being finally completed in 1948.

In any event, new through-running schemes seemed less attractive. London’s population began to decline: from 8.6 million people in 1939, to 8 million in 1961, to 6.8 million in 1981. Cars drew passengers away from railways. Furthermore, the Green Belt in particular, and more generally the introduction of Britain’s planning system, made it impossible to build new housing around commuter railways, reducing the value of more frequent services to these stations.

Even today, the outer reaches of the Central Line extensions go to places like Grange Hill and Theydon Bois, which are ‘mirror towns’: on one side of the tracks there is suburban development, on the other there are just fields. It was assumed in the 1930s that suburbia would rapidly spring up on the fields next to the stations, but in many cases there are streets that, quite literally, end when their builders were conscripted or redirected into war industries in 1939, and were never finished due to the Green Belt.

Trentwood Side in Enfield, North London. London stops at the end of this street where the trees are.

The tide did, however, start to turn. London’s population began to recover from its 1981 nadir, and the economic boom of the 1980s brought more traffic to the railways, many of them commuters into London.

In 1988, London implemented a through running project called Thameslink. This involved reopening the disused Snow Hill Tunnel, thereby restoring London’s first through-running service. Thameslink was an unusual project: although the passenger service had closed in 1916, the tunnel had been in use for freight until 1971, which meant it was easy to resurrect the service 15 years later. Although this brought immediate benefits, it was done cheaply, and 30 years later London had to spend six billion pounds on untangling track layouts, rebuilding stations and resignaling the route to get the most out of the Snow Hill Tunnel.

Unlike the original Thameslink, other through running projects would require much more substantial investment. But in the boom years of the late 1980s, it looked as though this would come. In 1989, the Central London Rail Study, commissioned jointly by the national government, British Railways and London Transport, proposed what eventually became the Elizabeth Line, a huge through-running scheme joining a suburban line running east from Liverpool Street into Essex with one running west from Paddington into Berkshire. It also proposed two other through-running schemes, which it expected to have lower benefits relative to their costs.

These proposed schemes were intended to kill two birds with one stone. As London grew, both the central trunks of the Tube and the suburban branches grew busier. The route that eventually became the Elizabeth Line would relieve the Central Line by providing a new parallel east-west route, as well as enabling through running of some of the suburban branches.

The early plan for what is now the Elizabeth line.

This was the first time that conditions seemed ripe to actually start building a brand-new through running line. In 1991, a bill to build the line was put before Parliament. In 1994, however, it was rejected, partly because an economic downturn had led to fewer commuters in London, but also perhaps because decision makers did not understand the benefits of through running: one cabinet minister was quoted as saying, ‘It went from nowhere to nowhere. No sane person has ever wanted to go to Shenfield’, one of the suburban termini of the line. But the idea did not go away. In 2000, another report recommended building the line. During the economic boom of the early 2000s, and with the growth in passenger numbers following railway privatization in 1995, the case for the line continued to be strong.

It was eventually approved by Parliament in 2008. Following delays and cost overruns, it finally opened in 2022.

The centerpiece of the Elizabeth Line is a 21 kilometer-long tunnel under the center of London, and out into the regenerated docklands. But in total, the Elizabeth Line trains travel 117 kilometers because of the two existing suburban lines it cannibalized.

The Elizabeth Line has been a huge success: within a year of opening, quarterly fare revenue exceeded predictions by £22 million. Nearly every station on the Line has surpassed its pre-COVID passenger numbers, even though in 2024 the average London station not on the Elizabeth Line had 10 percent fewer people than before COVID.

The Elizabeth Line has been transformative for places like Romford, a suburb of eastern London. Romford used to get direct trains to only Liverpool Street: it now has them to most of central London, Heathrow Airport, and the western suburbs. The trains also run twice as frequently as they used to. The rest of the city center (plus most of its suburbs) can be reached with one change of train. Because the trains to Romford no longer run into the terminus part of Liverpool Street, other services using the station have become more reliable as well.

Most importantly, this has been done cost-effectively. Although the Elizabeth Line tunnel was expensive, for the price of 21 kilometers of tunnel, London got a 117 kilometer-long railway network. In short, Romford has got most of the benefits of a connection to the London Underground, without needing to build an underground line all the way to the suburb.

The case for more through running

The Elizabeth Line was a success, but a costly one. It became viable only when London was booming and its railway lines were crying out for more capacity. If all through running schemes were like the Elizabeth Line, we might conclude it was an expensive luxury, useful only in the wealthiest and most transport-constrained cities.

Fortunately, this is not the case. For one thing, through running does not need to be as costly as the Elizabeth Line. As the table below shows, cities differ greatly in the costs at which they build through-running projects. These costs are usually correlated with the costs for railway projects in that country generally, suggesting their variation is mainly the result of regulatory and procurement systems rather than the particular physical features of the individual lines.

But as important as the cost per kilometer of track is the amount of track that needs to be made. Some cities, like Cologne, do not need to tunnel to allow trains to run through: they only need works to expand the city’s main station, or alter its layout. Where tunneling is necessary, it does not necessarily need to be on the scale of the Elizabeth Line. London is a megacity, but owing to its smaller size, a tunnel to connect Manchester’s suburban railway lines together would only be a couple of kilometers long, roughly a tenth of the length of the Elizabeth Line’s tunnel and more similar to the scale of the trunk tunnel of the Munich S-Bahn. Indeed, such a scheme was approved and was almost built in the early 1970s. It never went ahead due to pressures on the public finances, but similar projects were built in Liverpool, which used 1.5 kilometers of tunnel, and Newcastle, which used 5 kilometers.

Through running has potential in any city with a network of legacy suburban lines. In general, this is likely to be the case in countries that industrialized in the nineteenth century, when railways had been invented but metros had not.

Britain is a particularly striking example of this. British cities outside of London are notorious for their lack of metro and tram systems, but many of them actually have enormous suburban railway networks. The problem with these systems is not that they have poor coverage, but they have low frequency and poor interconnectivity. These are problems that can be solved by through running, turning them into something similar to modern metro systems, at a small fraction of the cost of developing such a metro from scratch.

Not all countries are so fortunate. China, for instance, developed large cities in the twentieth century with neither suburban railways nor modern metros. Today, the Chinese authorities want to improve their urban rail systems. But in the absence of suburban railways that can through run, that means developing vast underground metro systems from scratch at enormous expense.

Through running is a cost-effective way of upgrading pre-existing railway lines. This is beneficial for passengers who get a better quality of service, and in itself justifies through running. But through-run lines also are able to catalyze urban growth, by making better-connected areas desirable locations for development.

The Elizabeth Line has enabled development around stations like Woolwich, West Drayton and Southall, while new commuter towns have been proposed at Taplow and Iver. Meanwhile in Munich a brand-new urban quarter called Freiham is being built around a brand new S-Bahn station.

Dense residential development around the new Freiham S-Bahn station.

Other cities have designed entire expansion strategies around through running. In the 1930s, Copenhagen developed a high-capacity through-running system called the S-tog, which works much like the Munich S-Bahn. In the 1940s, Copenhagen developed its celebrated ‘finger plan’ for further development, with the city extending outward in urban ‘fingers’ along the lines of the S-tog, leaving open countryside in the areas between. Dozens of neighbourhoods are now clustered around S-tog stations, enjoying its fast, frequent, and highly interconnected service across Copenhagen and its environs.

The famous ‘finger plan’, with the five fingers corresponding to S-tog routes.

Crucially, the success or failure of through-running schemes does not depend on building new housing around the lines, because through-run lines are so much cheaper that they can often be justified purely on the basis of benefits of existing passengers. The reverse is usually true with metro schemes: due to their higher costs, they can only be financially viable if they are surrounded by high-density development. If that development does not materialize, either because of an economic downturn or because land-use regulations make it prohibitively expensive to build, the metro line will be an economic failure.

It is tempting to think that the most important ways to improve transport involve new technology: self-driving cars, flying taxis, or even e-scooters. But often, the best investments involve getting the most out of existing technology, through smaller investments that have a strong multiplier effect. Through running involves using a fairly old technology, deep bore tunneling, to improve an even older technology, commuter railways. 90 percent of London’s S-Bahn network is already built, and with Manchester this is closer to 95 percent. The opportunity is great in North America: Boston only needs a mile of tunnel, and Toronto and New York City already have the infrastructure for through running, but choose not to use it. By weaving together Victorian lines, these cities can get the best railway networks in the world. It’s not a free lunch, but most of it has already been paid for.

Karl Sack. ‘Aufgabe, Planung und Bau der S-Bahn München’ (1970) 21(9) Der Eisenbahner 257.

Deutsche Bahn has proposed a project, ‘München 21’ to replace Munich’s terminus with an underground through-station, as it has been doing in Stuttgart. The project, however, is unlikely to go ahead.

Each unit has a capacity of 544 passengers. In the peak, three units are coupled together to make a single train.

Munich has 2.7 million people within 30 kilometers of the center, which is roughly the extent of the S-Bahn. Paris has 11.3 million people within 40 kilometers, which is roughly the extent of the RER.

Alan A. Jackson, London’s Metropolitan Railway (David & Charles 1986), 47.

Alan A. Jackson, London’s Termini (2nd edn, David & Charles 1985), 201.

Only one line ended up being run onto the Tube in this period, the Watford DC Line, which plays host to part of the Bakerloo Line.

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