Category: Germany

S-Bahn and RegionalBahn

The American rail activist term regional rail refers to any mainline rail service short of intercity, which lumps two distinct service patterns. In some German cities, these patterns are called S-Bahn and RegionalBahn, with S-Bahn referring to urban rail running on mainline tracks and RegionalBahn to longer-range service in the 50-100 km range and sometimes even beyond. It’s useful to distinguish the two whenever a city wishes to invest in its regional rail network, because the key infrastructure for the two patterns is different.

As with many this-or-that posts of mine, the distinction is not always clear in practice. For one, in smaller cities, systems that are labeled S-Bahns often work more like RegionalBahn, for example in Hanover. Moreover, some systems have hybrid features, like the Zurich S-Bahn – and what I’ve advocated in American contexts is a hybrid as well. That said, it’s worth understanding the two different ends of this spectrum to figure out what the priority for rail service should be in each given city.

S-Bahn as urban rail

The key feature of the S-Bahn (or the Paris RER) is that it has a trunk that acts like a conventional urban rapid transit line. There are 6-14 stations on the trunks in the examples to keep in mind, often spaced toward the high end for rapid transit so as to provide express service through city center, and all trains make all stops, running every 3-5 minutes all day. Even if the individual branches run on a clockface schedule, people do not use the trunk as a scheduled railroad but rather show up and go continuously.

Moreover, the network layout is usually complementary with existing urban rail. The Munich S-Bahn was built simultaneously with the U-Bahn, and there is only one missed connection between them, The Berlin S-Bahn and U-Bahn were built separately as patchworks, but they too have one true missed connection and one possible miss that depends on which side of the station one considers the crossing point to be on. The RER has more missed connections with the Metro, especially on the RER B, but the RER A’s station choice was designed to maximize connections to the most important lines while maintaining the desired express stop spacing.

Urban rail lines rarely terminate at city center, and the same is true for S-Bahn lines. In cities whose rail stations are terminals, such as Paris, Munich, Frankfurt, and Stuttgart, there are dedicated tunnels for through-service; London is building such a tunnel in Crossrail, and built one for Thameslink, which has the characteristics of a hybrid. In Japan, too, the first priority for through-running is the most local S-Bahn-like lines – when there were only six tracks between Tokyo and Ueno, the Yamanote and Keihin-Tohoku Lines ran through, as did the Shinkansen, whereas the longer-range regional lines terminated at the two ends until the recent through-line opened.

The difference between an S-Bahn and a subway is merely that the subway is self-contained, whereas the S-Bahn connects to suburban branches. In Tokyo even this distinction is blurred, as most subway lines connect to commuter rail lines at their ends, often branching out.

RegionalBahn as intercity rail

Many regional lines descend from intercity lines that retooled to serve local traffic. Nearly every trunk line entering London from the north was built as a long-range intercity line, most commuter rail mainlines in New York are inner segments of lines that go to other cities or used to (even the LIRR was originally built to go to Boston, with a ferry connection), and so on.

In Germany, it’s quite common for such lines to maintain an intercity characteristic. The metropolitan layout of Germany is different from that of the English-speaking world or France. Single-core metro regions are rather small, except for Berlin. Instead, there are networks of independent metropolitan cores, of which the largest, the Rhine-Ruhr, forms an urban complex almost as large as the built-up areas of Paris and London. Even nominally single-core metro regions often have significant independent centers with long separate histories. I blogged about the Rhine-Neckar six months ago as one such example; Frankfurt is another, as the city is ringed by old cities including Darmstadt and Mainz.

But this is not a purely German situation. Caltrain connects what used to be two independent urban areas in San Francisco and San Jose, and many outer ends of Northeastern American commuter lines are sizable cities, such as New Haven, Trenton, Providence, and Worcester.

The intercity characteristic of such lines means that there is less need to make them into useful urban rail; going express within the city is more justifiable if people are traveling from 100 km away, and through-running is a lower priority. Frequency can be lower as well, since the impact of frequency is less if the in-vehicle travel time is longer; an hourly or half-hourly takt can work.

S-Bahn and RegionalBahn combinations

The S-Bahn and RegionalBahn concepts are distinct in history and service plan, but they do not have to be distinct in branding. In Paris, the distinction between Transilien and the RER is about whether there is through-running, and thus some lines that are RegionalBahn-like are branded as RER, for example the entire RER C. Moreover, with future extension plans, the RER brand will eventually take over increasingly long-distance regional service, for example going east to Meaux. Building additional tunnels to relieve the worst bottlenecks in the city’s transport network could open the door to connecting every Transilien line to the RER.

Zurich maintains separate brands for the S-Bahn and longer-distance regional trains, but as in Paris, the distinction is largely about whether trains terminate on the surface or run through either of the tunnels underneath Hauptbahnhof. Individual S-Bahn branches run every half hour, making extensive use of interlining to provide high frequency to urban stations like Oerlikon, and many of these branches go quite far out of the city. It’s not the same as the RER A and B or most of the Berlin S-Bahn, with their 10- and 15-minute branch frequencies and focus on the city and innermost suburbs.

But perhaps the best example of a regional rail network that really takes on lines of both types is that of Tokyo. In branding, the JR East network is considered a single Kanto-area commuter rail network, without distinctions between shorter- and longer-range lines. And yet, the rapid transit services running on the Yamanote, Keihin-Tohoku, and Chuo-Sobu Lines are not the same as the highly-branched network of faster, longer-range lines like Chuo Rapid, Yokosuka, Sobu Rapid, and so on.

The upshot is that cities do not need to neatly separate their commuter rail networks into two separate brands as Berlin does. The distinction is not one of branding for passengers, but one of planning: should a specific piece of infrastructure be S-Bahn or RegionalBahn?

Highest and best use for infrastructure

Ordinarily, the two sides of the spectrum – an S-Bahn stopping every kilometer within the city, and a RegionalBahn connecting Berlin with Magdeburg or New York with New Haven – are so different that there’s no real tradeoff between them, just as there is no tradeoff between building subways and light rail in a city and building intercity rail. However, they have one key characteristic leading to conflict: they run on mainline track. This means that transportation planners have to decide whether to use existing mainline tracks for S-Bahn or RegionalBahn service.

Using different language, I talked about this dilemma in Boston’s context in 2012. The situation of Boston is instructive even in other cities, even outside the United States, purely because its commuter rail service is so bad that it can almost be viewed as blank slate service on existing infrastructure. On each of the different lines in Boston, it’s worth asking what the highest and best use for the line is. This really boils down to two questions:

  1. Would the line fill a service need for intra-urban travel?
  2. Does the line connect to important outlying destinations for which high speed would be especially beneficial?

In Boston, the answer to question 1 is for the most part no. Thirty to forty years ago the answer would have been yes for a number of lines, but since then the state has built subway lines in the same rights-of-way, ignorant of the development of the S-Bahn concept across the Pond. The biggest exceptions are the Fairmount Line through Dorchester and the inner Fitchburg Line through suburbs of Cambridge toward Brandeis.

On the Fairmount Line the answer to question 2 is negative as well, as the line terminates within Boston, which helps explain why the state is trying to invest in making it a useful S-Bahn with more stops, just without electrification, high frequency, fare integration, or through-service north of Downtown Boston. But on the Fitchburg Line the answer to question 2 is positive, as there is quite a lot of demand from suburbs farther northwest and a decent anchor in Fitchburg itself.

The opposite situation to that of Fairmount is that of the Providence Line. Downtown Providence is the largest job center served by the MBTA outside Boston; the city ranks third in New England in number of jobs, behind Boston and Cambridge and ahead of Worcester and Hartford. Fast service between Providence and Boston is obligatory. However, Providence benefits from lying on the Northeast Corridor, which can provide such service if the regional trains are somewhat slower; this is the main justification for adding a handful of infill stops on the Providence Line.

In New York, the situation is the most complicated, befitting the city’s large size and constrained location. On most lines, the answers to both questions is yes: there is an urban rail service need, either because there is no subway service (as in New Jersey) or because there is subway service and it’s overcrowded (as on the 4/5 trains paralleling the Metro-North trunk and on the Queens Boulevard trains paralleling the LIRR trunk); but at the same time, there are key stations located quite far from the dense city, which can be either suburban centers 40 km out or, in the case of New Haven, an independent city more than 100 km out.

Normally, in a situation like New York’s, the solution should be to interline the local lines and keep the express lines at surface terminals; London is implementing this approach line by line with the Crossrail concept. Unfortunately, New York’s surface terminals are all outside Manhattan, with the exception of Grand Central. Penn Station has the infrastructure for through-running because already in the 1880s and 90s, the ferry transfers out of New Jersey and Brooklyn were onerous, so the Pennsylvania Railroad invested in building a Manhattan station fed by east-west tunnels.

I call for complete through-running in New York, sometimes with the exception of East Side Access, because of the island geography, which makes terminating at the equivalent of Gare du Nord or Gare de Lyon too inconvenient. In other cities, I might come to different conclusions – for example, I don’t think through-running intercity trains in Chicago is a priority. But in New York, this is the only way to guarantee good regional rail service; anything else would involve short- and long-range trains getting in each other’s way at Penn Station.

The High-Speed Rail Germany Needs

I’ve argued in two previous posts that Germany needs to build a complete high-speed rail network, akin to what China, Japan, France, South Korea, and Spain have built. Here is the network that Germany should build in more detail:

The red lines denote high-speed lines, some legacy 250-280 km/h lines but most built to support 300-320 km/h, that are justifiable within the context of domestic travel. Some of these already exist, such as the Frankfurt-Cologne line and the majority of the Berlin-Munich line; Berlin-Hamburg is a legacy line upgraded to 230, currently tied with Frankfurt-Cologne for fastest average speed between two major cities in Germany. A handful of red lines are key legacy connections, i.e. Dresden-Leipzig and Dortmund-Duisburg. Some more detail on the red lines is available in Google Maps.

The blue lines denote high-speed lines, generally built to 300, that only make sense in an international context. The lines in France are the LGV Est and its short low-speed branch across the border to Saarbrücken. In Belgium the line preexists as well as HSL 3 and HSL 4, but is quite slow, averaging only 140 km/h from Brussels to Aachen thanks to a combination of a slow segment to Leuven and a speed-restricted western approach to Liege. In the Netherlands, Switzerland, Czechia, Austria, and Poland the lines are completely speculative, though in Czechia a high-speed line from Prague to Dresden is under study.

Update 8/19: here is another map of the same network, color-coded differently – red is proposed lines (most by me, a few officially), yellow is lines under construction, blue is existing lines, black is low-speed connections. Note that outside Berlin’s northern approaches, urban approaches are not colored black even if they’re slow.

Trip times

To compute trip times, I dusted off my train performance calculator, linked here. The parameters I used are those planned for the next-generation Velaro (“Velaro Novo“), i.e. a power-to-weight ratio of 20.7 kW/t and an initial acceleration rate of 0.65 m/s^2; the quadratic air resistance term is 0.000012, as any higher term would make it impossible to reach speeds already achieved in tests. On curves, the lateral acceleration in the horizontal plane is set at 2.09 m/s^2 on passenger-priority lines, mirroring what is achieved on Frankfurt-Cologne, and 1.7 elsewhere, accounting for lower superelevation.

These are aggressive assumptions and before running the code, I did not expect Berlin-Munich to be so fast. With intermediate stops at Erfurt, Nuremberg, and maybe also Ingolstadt, this city pair could be connected in 2.5 hours minus a few minutes for interchange time at the terminals. In general, all trip times printed on the map are a few minutes slower than what is achievable even with some schedule padding, corresponding to dwell times at major through-stations plus interchange at terminals. The upshot is that among the largest metro areas in Germany, the longest trips are Hamburg-Stuttgart at 3:30 minus change and Hamburg-Munich at 3:15 minus change; nothing else is longer than 3 hours.

The stopping pattern should be uniform. That is, every 320 km/h train between Berlin and Munich should stop exactly at Berlin Südkreuz, Erfurt, Nuremberg, and maybe Ingolstadt. If these trains skip Ingolstadt, it’s fine to run some 250 km/h trains part of the way, for example between Munich and Nuremberg and then northwest on legacy track to Würzburg and Frankfurt, with the Ingolstadt station added back. Similarly, from Hamburg south, every train should stop at Hanover, Göttingen, Kassel, and Fulda.

In certain cases, the stopping pattern should be decided based on whether trains can make a schedule in an exact number of quarter-hours. That is, if it turns out that Munich-Nuremberg with an intermediate stop in Ingolstadt takes around 42 minutes then the Ingolstadt stop should be kept; but if it takes 46 minutes, then Ingolstadt should be skipped, and instead of running in the depicted alignment, the line should stay near the Autobahn and bypass the city in order to be able to make it in less than 45 minutes. I think Ingolstadt can still be kept, but one place where the map is likely to be too optimistic is Stuttgart-Munich; Ulm may need to be skipped on the fastest trains, and slower trains should pick up extra stops so as to be 15 minutes slower.

Frequency and service planning

Today, the frequency on the major city pairs is hourly. Under the above map, it should be half-hourly, since the faster trip times will induce more ridership. As a sanity check, TGVs connect Paris with each of Lyon’s two stations hourly off-peak and twice an hour at the peak. Paris is somewhat larger than the entire Rhine-Ruhr, Lyon somewhat smaller than Stuttgart or Munich and somewhat larger than the Rhine-Neckar. But the ICE runs somewhat smaller trains and has lower occupancy as it runs trains on a consistent schedule all day, so matching the peak schedule on the TGV is defensible.

The upshot is that Berlin can probably be connected every 30 minutes to each of Hamburg, Munich, Frankfurt, Cologne, Düsseldorf, and the Ruhr proper. Frankfurt-Munich is likely to be every 30 minutes, as are Hamburg-Frankfurt and Hamburg-Munich. To further improve network connectivity, the schedule at Erfurt should be set in such a way that Hamburg-Munich and Berlin-Frankfurt trains are timed with a cross-platform transfer, regardless of the pulse anywhere else. A few connections to smaller cities should be hourly, like Berlin-Bremen (with a timed transfer at Hanover to Hamburg-Frankfurt or Hamburg-Munich), Leipzig-Munich, Leipzig-Frankfurt, and Frankfurt-Basel.

The loop track around Frankfurt is based on a real plan for mainline through-tracks at the station, currently in the early stages of construction. The near-Autobahn loop is not included, but such a connection, if done at-grade, could provide value by letting trains from Munich enter the station from the east and then continue northwest toward Cologne without reversing direction.

If the international connections are built as planned, then additional hourly and even more frequent connections can be attractive. Zurich-Stuttgart might well even support a train every half hour, going all the way to Frankfurt and thence to either Cologne or Berlin. Similarly, Berlin-Frankfurt-Paris could plausibly fill an hourly train if Frankfurt-Paris is cut to 2:30 via Saarbrücken, and maybe even if it takes three hours via Karlsruhe.

The one exception to this interconnected mesh is Fulda-Würzburg. The Hanover-Würzburg line was built as a single 280 km/h spine through West Germany with low-speed branches down to Frankfurt and Munich. Unfortunately, completing the Würzburg-Nuremberg segment has little value: Munich-Frankfurt would be almost as fast via Stuttgart, and Hamburg-Munich would be half an hour faster via Erfurt with not much more construction difficulty on Göttingen-Erfurt. Fulda-Würzburg should thus be a shuttle with timed transfers at Fulda, potentially continuing further south at lower speed to serve smaller markets in Bavaria.

Cost

The domestic network depicted on the map is 1,300 km long, not counting existing or under-construction lines. Some lines require tunneling, like Erfurt-Fulda-Frankfurt, but most do not; the heaviest lifting has already been done, including between Erfurt and Nuremberg and around Stuttgart for Stuttgart 21 and the under-construction high-speed line to Ulm. I doubt 100 km of tunnel are necessary for this network; for comparison, Hanover-Würzburg alone has 120 km of tunnel, as the line has very wide curve radii to support both high-speed passenger rail and low-speed freight without too much superelevation. The cost should be on the order of 30-40 billion euros.

The international network is more complex. Berlin-Prague is easy on the German side and even across the border, and the only real problems are on the Czech side, especially as Czech planners insist on serving Usti on the way with a city center station. But Stuttgart-Zurich is a world of pain, and Frankfurt-Saarbrücken may require some tunneling through rolling terrain as well, especially around Saarbrücken itself.

Even with the international lines added in, the German share of the cost should not be too onerous. Getting everything in less than 50 billion euros should not be hard, even with some compromises with local NIMBYs. Even on an aggressive schedule aiming for completion by 2030, it’s affordable in a country where the budget surplus in 2018 was €58 billion across all levels of government and where there are signs of impending recession rather than inflation.

With its mesh of medium-size cities all over the country following plausible lines, Germany is well-placed to have the largest high-speed rail network in Europe. It has the ability to combine the precise scheduling and connections of Switzerland and the Netherlands with the high point-to-point speeds of France and Spain, creating a system that obsoletes domestic flights and competes well with cars and intercity buses. The government can implement this; all it takes is the political will to invest in a green future.

Why You Should Complete High-Speed Lines

Some countries build complete high-speed rail networks, on which one can travel between cities almost entirely at high speed, such as France, Japan, and China. Others build partial networks, mixing low- and high-speed travel, such as Germany. The planning lingo in the latter is “strategic bypass” or “strategic connection.” And yet, there is nothing strategic about most mixed lines. If a line between two cities is partly high-speed and partly low-speed, it is usually strategic to complete the high-speed line and provide fast travel – the benefits will exceed those of having built the original high-speed partial segment. Since Germany’s rail network largely consists of such mixed lines, the benefits of transitioning to full high-speed rail here are large.

The arguments I’m about to present are not entirely new. To some extent, I discussed an analog years ago when arguing that in the presence of a complete high-speed line, the benefits of building further extensions are large; this post is a generalization of what I wrote in 2013. Then, a few months ago, I blogged about positive and negative interactions. I didn’t discuss high-speed rail, but the effect of travel time on ridership is such that different segments of the same line positively interact.

The upshot is that once the basics of a high-speed rail networks are in place, the benefit-cost ratio of further extensions is high. In a country with no such network, the first line or segments may look daunting, such as India or the UK, but once it’s there, the economics of the rest tend to fall into place. It takes a while for returns to diminish below the point of economic viability.

A toy model

Take a low-speed rail line:

Now build a high-speed line parallel to half of it and connect it with the remaining half:

You will have reduced trip time from 4 hours to 3 hours. This has substantial benefits in ridership and convenience. But then you can go all the way and make the entire line fast:

Are there diminishing returns?

No.

The benefits of reducing travel time per unit of absolute amount of time saved always increase in speed; they never decrease. The gravity model holds that ridership follows an inverse square law in total cost, including ticket fare and the passengers’ value of time, which time includes access and egress time. Reducing in-vehicle travel time by a fixed amount, say an hour, increases ridership more if the initial travel time is already lower.

This is on top of reductions in operating costs coming from higher speed. Trains on high-speed track consume less electricity than on legacy track, because they cruise at a constant speed, and because head-end power demand scales with time rather than distance traveled. Crew wages per kilometer are lower on faster trains. And the cost of rolling stock procurement and maintenance is spread across a longer distance if the same train is run more kilometers per year. In the toy model, there are actually increasing returns coming from rolling stock costs: upgrading half the line to high speed requires running an expensive high-speed train on the entire line, whereas completing the high-speed line does not require increasing the cost per unit of rolling stock.

Diminishing returns do occur, but only in the context of an increase in top speed, not in that of speeding up slow segments to match the top speed of faster segments. In that context, benefits do diminish and costs do rise, but that is not the same as completing high-speed lines.

As the maximum speed is increased from 160 to 200 km/h, the train speeds up from 22.5 seconds per kilometer to 18. To provide the same increase further, that is to reduce the time taken to traverse a kilometer by a further 4.5 seconds to 13.5, the speed must increase to 266.67 km/h. To provide the same 4.5-second increase once more, the speed must increase to 400. Curve radius is proportional to the square of speed, so these increases in speed must be accompanied by much more exacting track geometry. Tunnels may well be unavoidable at the higher speeds in topography that could accommodate 200-250 entirely at-grade.

What’s more, operating costs rise too as top speed increases. The electricity consumption on a 300 km/h cruise is lower than on a legacy line on which trains transition back and forth between 200 and 100 and all speeds in between, but the electricity consumption on a 350 km/h cruise is definitely higher than on a 250 km/h cruise.

However, what is relevant to the decision of what standards to build a line to is not relevant to the decision of how far to extend this standard. Once a 300 km/h segment has been built, with a dedicated fleet of trains that cost 30 million per 200-meter set, the returns to upgrading the entire segment the train runs on are higher than those of just building the initial segment.

Can some strategic segments be easier to build than others?

Yes, but only in one specific situation: that of an urban area. The toy model says nothing of construction costs – in effect, it assumes the cost of making the first 200 km fast is the same as that of making the next 200 km fast. In reality, different areas may have different construction challenges, making some parts easier to build than others.

However, if the construction challenge is mountainous topography, then the higher cost of mountain tunnels balance out the greater benefit of fast trains across mountains. The reason is that in practice, legacy rail lines are faster in flat terrain than in the mountains, where past construction compromises led to sharp curves.

This situation is different in urban areas. In urban areas as in the mountains, costs are higher – land acquisition is difficult, and tunnels may be required in areas where the alternative is buying out entire city blocks. But unlike in the mountains, the existing rail line may well be reasonably straight, permitting average speeds in the 120 km/h area rather than the 70 km/h area. In that case, it may be advisable to postpone construction until later, or even keep the legacy alignment.

One example is the Ruhr area. The tracks between Dortmund and Duisburg are not high-speed rail – the fastest trains do the trip in about 34 minutes, an average speed of about 95 km/h. Speeding them up by a few minutes is feasible, but going much below 30 minutes is not. Thus, even if there is a 300 km/h line from Dortmund to points east, the returns to the same speedup between Dortmund and Duisburg are low. (Besides which, Dortmund is the largest city in the Ruhr, and the second largest, Essen, in the middle between Dortmund and Duisburg.)

Another is Connecticut. East of New Haven, there is relatively little urban development, and constructing a 300-360 km/h line roughly along the right-of-way of I-95 poses few challenges. West of New Haven, such construction would require extensive tunneling and elevated construction – and the legacy line is actually somewhat less curvy, it’s just slower because of poor timetable coordination between Amtrak’s intercity trains and Metro-North’s regional trains. While the returns to building 250-300 km/h bypasses around the line’s slowest points in southwestern Connecticut remain high enough to justify the project, they’re lower than those in southeastern Connecticut.

The situation in Germany

On the following map, black denotes legacy lines and red denotes purpose-built 300 km/h high-speed lines:

The longer red segment, through Erfurt, is the more challenging one, including long tunnels through the mountains between Thuringia and Bavaria. The complexity and cost of construction led to extensive media controversy. In particular, the choice of the route through Erfurt came about due to Thuringia’s demands that it serve its capital rather than smaller cities; DB’s preference would have been to build a more direct Leipzig-Nuremberg route, which would have had shorter tunnels as the mountains in eastern Thuringia are lower and thinner.

Since then, a lot of water has passed under the bridge. The route opened at the end of 2017 and cut travel time from 6 hours to 4, bypassing the slowest mountain segment, and is considered a success now. In the North German Plain, the trains mostly cruise at 200 km/h, and trains traverse the 163.6 km between Berlin and Halle in 1:09-1:11, an average speed of 140 km/h.

Nonetheless, the benefits of painting the entire map red, roughly from the city limits of Berlin to those of Munich, are considerable. The North German Plain’s flat topography enables trains to average 140 km/h, but also means that building a high-speed line would be cheap – around 137 km of new-build line would be needed, all at-grade, at a cost of about €2.5 billion, which would cut about half an hour from the trip time. In Bavaria, the topography is rougher and consequently the legacy trains’ average speed is lower, but nonetheless, high-speed rail can be built with cut-and-fill, using 4% grades as on the Cologne-Frankfurt line.

I’m uncertain about the exact travel time benefits of such a high-speed line. I put a route through my train performance calculator and got about 2.5 hours with intermediate stops at Südkreuz, Erfurt, Nuremberg, and possibly Ingolstadt (skipping Ingolstadt saves 3 minutes plus the dwell time), using the performance characteristics of the next-generation Velaro. But I’m worried that my speed zones are too aggressive and that the schedule should perhaps accommodate TGVs coming from Paris via Frankfurt, so I won’t commit to 2:30; however, 2:45-2:50 should be doable, even with some unforeseen political compromises.

But even with less optimistic assumptions about trip times, Germany should do it. If it was justifiable to spend €10 billion on reducing trip times from 6 hours to just under 4, it should be justifiable to spend around half that amount on reducing trip times by another hour and change.

Deutschlandtakt and Country Size

Does the absolute size of a country matter for public transport planning? Usually it does not – construction costs do not seem to be sensitive to absolute size, and the basics of rail planning do not either. That Europe’s most intensely used mainline rail networks are those of Switzerland and the Netherlands, two geographically small countries, is not really about the inherent benefits of small size, but about the fact that most countries in Europe are small, so we should expect the very best as well as the very worst to be small.

But now Germany is copying Swiss and Dutch ideas of nationally integrated rail planning, in a way that showcases where size does matter. For decades Switzerland has had a national clockface schedule in which all trains are coordinated for maximum convenience of interchange between trains at key stations. For example, at Zurich, trains regularly arrive just before :00 and :30 every hour and leave just after, so passengers can connect with minimum wait. Germany is planning to implement the same scheme by 2030 but on a much bigger scale, dubbed Deutschlandtakt. This plan is for the most part good, but has some serious problems that come from overlearning from small countries rather than from similar-size France.

In accordance with best industry practices, there is integration of infrastructure and timetable planning. I encourage readers to go to the Ministry of Transport (BMVI) and look at some line maps – there are links to line maps by region as well as a national map for intercity trains. The intercity train map is especially instructive when it comes to scale-variance: it features multihour trips that would be a lot shorter if Germany made a serious attempt to build high-speed rail like France.

Before I go on and give details, I want to make a caveat: Germany is not the United States. BMVI makes a lot of errors in planning and Deutsche Bahn is plagued by delays; these are still basically professional organizations, unlike the American amateur hour of federal and state transportation departments, Amtrak, and sundry officials who are not even aware Germany has regional trains. As in London and Paris, the decisions here are defensible, just often incorrect.

Run as fast as necessary

Switzerland has no high-speed rail. It plans rail infrastructure using the maxim, run trains as fast as necessary, not as fast as possible. Zurich, Basel, and Bern are around 100 km from one another by rail, so the federal government invested in speeding up the trains so as to serve each city pair in just less than an hour. At the time of this writing, Zurich-Bern is 56 minutes one-way and the other two pairs are 53 each. Trains run twice an hour, leaving each of these three cities a little after :00 and :30 and and arriving a little before, enabling passengers to connect to onward trains nationwide.

There is little benefit in speeding up Switzerland’s domestic trains further. If SBB increases the average speed to 140 km/h, comparable to the fastest legacy lines in Sweden and Britain, it will be able to reduce trip times to about 42 minutes. Direct passengers would benefit from faster trips, but interchange passengers would simply trade 10 minutes on a moving train for 10 minutes waiting for a connection. Moreover, drivers would trade 10 minutes working on a moving train for 10 minutes of turnaround, and the equipment itself would simply idle 10 minutes longer as well, and thus there would not be any savings in operating costs. A speedup can only fit into the national takt schedule if trains connect each city pair in just less than half an hour, but that would require average speeds near the high end of European high-speed rail, which are only achieved with hundreds of kilometers of nonstop 300 km/h running.

Instead of investing in high-speed rail like France, Switzerland incrementally invests in various interregional and intercity rail connections in order to improve the national takt. To oversimplify a complex situation, if a city pair is connected in 1:10, Switzerland will invest in reducing it to 55 minutes, in order to allow trains to fit into the hourly takt. This may involve high average speeds, depending on the length of the link. Bern is farther from Zurich and Basel than Zurich and Basel are from each other, so in 1996-2004, SBB built a 200 km/h line between Bern and Olten; it has more than 200 trains per day of various speed classes, so in 2007 it became the first railroad in the world to be equipped with ETCS Level 2 signaling.

With this systemwide thinking, Switzerland has built Europe’s strongest rail network by passenger traffic density, punctuality, and mode share. It is this approach that Germany seeks to imitate. Thus, the Deutschlandtakt sets up control cities served by trains on a clockface schedule every 30 minutes or every hour. For example, Erfurt is to have four trains per hour, two arriving just before :30 and leaving just after and two arriving just before :00 and leaving just after; passengers can transfer in all directions, going north toward Berlin via either Leipzig or Halle, south toward Munich, or west toward Frankfurt.

Flight-level zero airlines

Richard Mlynarik likes to mock the idea of high-speed rail as conceived in California as a flight-level zero airline. The mockery is about a bunch of features that imitate airlines even when they are inappropriate for trains. The TGV network has many flight-level zero airline features: tickets are sold using an opaque yield management system; trains mostly run nonstop between cities, so for example Paris-Marseille trains do not stop at Lyon and Paris-Lyon trains do not continue to Marseille; frequency is haphazard; transfers to regional trains are sporadic, and occasionally (as at Nice) TGVs are timed to just miss regional connections.

And yet, with all of these bad features, SNCF has higher long-distance ridership than DB, because at the end of the day the TGVs connect most major French cities to Paris at an average speed in the 200-250 km/h range, whereas the fastest German intercity trains average about 170 and most are in the 120-150 range. The ICE network in Germany is not conceived as complete lines between pairs of cities, but rather as a series of bypasses around bottlenecks or slow sections, some with a maximum speed of 250 and some with a maximum speed of 300. For example, between Berlin and Munich, only the segments between Ingolstadt and Nuremberg and between Halle and north of Bamberg are on new 300 km/h lines, and the rest are on upgraded legacy track.

Even though the maximum speed on some connections in Germany is the same as in France, there are long slow segments on urban approaches, even in cities with ample space for bypass tracks, like Berlin. The LGV Sud-Est diverges from the classical line 9 kilometers outside Paris and permits 270 km/h 20 kilometers out; on its way between Paris and Lyon, the TGV spends practically the entire way running at 270-300 km/h. No high-speed lines get this close to Berlin or Munich, even though in both cities, the built-up urban area gives way to farms within 15-20 kilometers of the train station.

The importance of absolute size

Switzerland and the Netherlands make do with very little high-speed rail. Large-scale speedups are of limited use in both countries, Switzerland because of the difficulty of getting Zurich-Basel trip times below half an hour and the Netherlands because all of its major cities are within regional rail distance of one another.

But Germany is much bigger. Today, ICE trains go between Berlin and Munich, a distance of about 600 kilometers, in just less than four hours. The Deutschlandtakt plan calls for a few minutes’ speedup to 3:49. At TGV speed, trains would run about an hour faster, which would fit well with timed transfers at both ends. Erfurt is somewhat to the north of the midpoint, but could still keep a timed transfer between trains to Munich, Frankfurt, and Berlin if everything were sped up.

Elsewhere, DB is currently investing in improving the line between Stuttgart and Munich. Trains today run on curvy track, taking about 2:13 to do 250 km. There are plans to build 250 km/h high-speed rail for part of the way, targeting a trip time of 1:30; the Deutschlandtakt map is somewhat less ambitious, calling for 1:36, with much of the speedup coming from Stuttgart21 making the intercity approach to Stuttgart much easier. But with a straight line distance of 200 km, even passing via Ulm and Augsburg, trains could do this trip in less than an hour at TGV speeds, which would fit well into a national takt as well. No timed transfers are planned at Augsburg or Ulm. The Baden-Württemberg map even shows regional trains (in blue) at Ulm timed to just miss the intercity trains to Munich. Likewise, the Bavaria map shows regional trains at Augsburg timed to just miss the intercity trains to Stuttgart.

The same principle applies elsewhere in Germany. The Deutschlandtakt tightly fits trains between Munich and Frankfurt, doing the trip in 2:43 via Stuttgart or 2:46 via Nuremberg. But getting Munich-Stuttgart to just under an hour, together with Stuttgart21 and a planned bypass of the congested Frankfurt-Mannheim mainline, would get Munich-Frankfurt to around two hours flat. Via Nuremberg, a new line to Frankfurt could connect Munich and Frankfurt in about an hour and a half at TGV speed; even allowing for some loose scheduling and extra stops like Würzburg, it can be done in 1:46 instead of 2:46, which fits into the same integrated plan at the two ends.

The value of a tightly integrated schedule is at its highest on regional rail networks, on which trains run hourly or half-hourly and have one-way trip times of half an hour to two hours. On metro networks the value is much lower, partly because passengers can make untimed transfers if trains come every five minutes, and partly because when the trains come every five minutes and a one-way trip takes 40 minutes, there are so many trains circulating at once that the run-as-fast-as-necessary principle makes the difference between 17 and 18 trainsets rather than that between two and three. In a large country in which trains run hourly or half-hourly and take several hours to connect major cities, timed transfers remain valuable, but running as fast as necessary is less useful than in Switzerland.

The way forward for Germany

Germany needs to synthesize the two different rail paradigms of its neighbors – the integrated timetables of Switzerland and the Netherlands, and the high-speed rail network of France.

High investment levels in rail transport are of particular importance in Germany. For too long, planning in Germany has assumed the country would be demographically stagnant, even declining. There is less justification for investment in infrastructure in a country with the population growth rate of Italy or of last decade’s Germany than in one with the population growth rate of France, let alone one with that of Australia or Canada. However, the combination of refugee resettlement and a very strong economy attracting European and non-European work migration is changing this calculation. Even as the Ruhr and the former East Germany depopulate, we see strong population growth in the rich cities of the south and southwest as well as in Berlin.

The increased concentration of German population in the big cities also tilts the best planning in favor of the metropolitan-centric paradigm of France. Fast trains between Berlin, Frankfurt, and Munich gain value if these three cities grow in population whereas the smaller towns between them that the trains would bypass do not.

The Deutschlandtakt’s fundamental idea of a national integrated timed transfer schedule is good. However, a country the size and complexity of Germany needs to go beyond imitating what works in Switzerland and the Netherlands, and innovate in adapting best practices for its particular situation. People keep flying domestically since the trains take too long, or they take buses if the trains are too expensive and not much faster. Domestic flights are not a real factor in the Netherlands, and barely at all in Switzerland; in Germany they are, so trains must compete with them as well as with flexible but slow cars.

The fact that Germany already has a functional passenger rail network argues in favor of more aggressive investment in high-speed rail. The United States should probably do more than just copy Switzerland, but with nonexistent intercity rail outside the Northeast Corridor and planners who barely know that Switzerland has trains, it should imitate rather than innovating. Germany has professional planners who know exactly how Germany falls short of its neighbors, and will be leaving too many benefits on the table if it decides that an average speed of about 150 km/h is good enough.

Germany can and should demand more: BMVI should enact a program with a budget in the tens of billions of euros to develop high-speed rail averaging 200-250 km/h connecting all of its major cities, and redo the Deutschlandtakt plans in support of such a network. Wedding French success in high-speed rail and Swiss and Dutch success in systemwide rail integration requires some innovative planning, but Germany is capable of it and should lead in infrastructure construction.

What is Light Rail, Anyway?

I’ve been asked on Twitter about the differences between various kinds of urban rail transit. There is a lot of confusion about the term light rail in English, since it can be used for urban public transport typologies that have little to do with one another. The best way to think about urban rail (other than regional rail) is to use the following schema:

Slow in center Fast in center
Slow in outlying areas Tramway Subway-surface
Fast in outlying areas Tram-train Rapid transit

 

In American parlance, all four have been called light rail: subway-surface and tram-train lines are always called light rail, and officially so are tramways; then one full rapid transit line, the Green Line in Los Angeles, is called light rail as it runs light rail vehicles (LRVs) rather than subways. Nonetheless, in this post I will ignore what things are called and focus on their speed.

In this context, fast and slow refer to right-of-way quality. A tramway in a low-density city with little traffic and widely separated stops may well be faster than a rapid transit line with many stops, such as most Paris Metro lines, but relative to the local urban typology the tramway is still slow while the metro is fast.

The two hybrid forms – subway-surface and tram-train – differ in where they focus higher-speed service. On a subway-surface line, the city center segment is in a subway and then the line branches farther out, for examples the Boston Green Line, San Francisco Muni Metro, Philadelphia Subway-Surface Lines, and Frankfurt and Cologne U-Bahn networks. On a tram-train, the train is fast outside city center, where it runs in a dedicated surface right-of-way, but then in city center it runs in tramway mode on the street at lower speed; the Karlsruhe tram-train is one such example, as are virtually all postwar light rail systems in the United States and Canada.

Aberrations

The 2*2 typology simplifies the situation somewhat. There exist lines that don’t fully obey it, and instead change between metro and streetcar mode haphazardly. Some of the Cologne lines go back and forth. Buffalo has a single light rail line without branches, dubbed the Buffalo Metro Rail, running on the surface in the center and in a greenfield tunnel farther out toward Amherst and the university campus. Frankfurt’s U1/2/3/8 trunk is the opposite of Buffalo, running in a tunnel in the center and on the surface farther out even downstream of the branch point. The Los Angeles Blue Line is underground at Metro Center but then runs on the surface, transitions to a grade-separated right-of-way later, and finally drops back to streetcar mode in Downtown Long Beach.

The most fascinating case is that of the Boston Green Line D branch. It is technically rapid transit, since the trunk line is in a tunnel alongside the other branches whereas the branch itself is a former commuter rail line; it is called light rail because it runs LRVs, like the Los Angeles Green Line, and shared the trunk with the B, C, and E branches, all of which have surface segments. But conceptually, it presages most proper American light rail lines: it was built in the 1950s as suburban-oriented rapid transit, with park-and-rides and downtown-focused service, creating a paradigm that postwar metros like BART and the Washington Metro would sometimes follow and that light rail systems from the 1980s onward (San Diego, Portland, etc.) always would.

Nonetheless, such aberrations are uncommon enough that the 2*2 simplification works when explaining what cities should be building.

Right-of-way availability

Cities are more likely to build fast trains when there is preexisting right-of-way for them. The Karlsruhe Zweisystem is based on using the area’s extensive legacy mainline network, on which LRVs run in train mode, and then diverging toward city center in streetcar mode. Jarrett Walker has a good post about Karlsruhe specifically: there is no good right-of-way with which to drag the Stadtbahn into city center in train mode, and thus the alternative to a tram-train is an expensive tunnel; such a tunnel is under construction now, at the cost of about €1 billion, but as Karlsruhe is a small city, it comes a generation after the tram-train system was put into place.

North American light rail systems often use mainline rail corridors as well, but thanks to federal regulations as well as weak regional rail systems, they almost never use mainline tracks; the Blue Line in San Diego, the first tram-train in the United States, is one of very few exceptions, and even then it shares track with a very lightly-used freight line, rather than with a frequent S-Bahn as in Karlsruhe. It is more common for North American tram-trains to run in disused corridors, on new tracks parallel to the mainline, or even in highway medians.

Reusing legacy rail lines and running in freeway medians are not unique to tram-trains. Rapid transit does both outside city center; the first subway network in the world, the London Underground, makes extensive use of branches of former commuter lines, and even shares track with a still-active one on a portion of the Watford DC Line. New York, likewise, connected former excursion lines in Brooklyn to the subway, forming most of the Coney Island-bound system, and later did the same with the LIRR in the Rockaways, now carrying branches of the A train. It is usually easy to spot whether an urban rail line descends from a legacy branch line – if it does then it is very unlikely to follow a single street (none of the lines serving Coney Island does), whereas if it doesn’t then it is usually a subway or el on a major arterial (such as Fourth Avenue in Brooklyn).

The upshot is that cities are likelier to build tram-trains and rapid transit in preference to tramways and subway-surface lines if they have high-quality right-of-way. New York and London were unlikely to build subway-surface lines in the early 20th century either way, but the high density of their metro networks in Southern Brooklyn and West London respectively can be explained by the extent of preexisting legacy lines in these areas. Comparable areas that did not have such good connections, for example Queens, have much less rapid transit coverage.

While this issue in theory affects tram-trains and rapid transit equally, in practice it is especially relevant to tram-trains. Rapid transit is more expensive, so it is likely to be built in larger and denser cities, where it is more acceptable to just tunnel under difficult segments. Tram-trains are present in smaller cities – Calgary, Edmonton, Karlsruhe, and so on – as well as in American Sunbelt cities that are so auto-oriented that they have the public transport of European cities one third or even one tenth their size. In those cities, tunneling is harder to justify, so the train goes where it can go cheaply. Downtown transit malls like those of Portland and Calgary are the least bad solution for connecting fast lines from the suburbs to provide better city center coverage and connect to lines on the other side of the region.

Subway-surface branching

Subway-surface lines are fast in city center and slow outside of it. Moreover, in city center their right-of-way segregation (in a tunnel in all of the American cases) means there is more capacity than on the surface. This makes branching especially attractive. Indeed, in all three American cases – Boston, Philadelphia, San Francisco – the subway-surface line has four to five branches.

Outside the United States, subway-surface branching is more complicated. In Frankfurt, the U4/5 and U6/7 lines work as in the United States, but with only two branches per trunk rather than four or five; but the U1/2/3 line has a surface segment on the mainline. In Cologne, there is extensive reverse-branching (see map), and while most of the system runs in subway-surface mode, one line runs in tramway mode through city center but then drops to a tunnel in Deutz and splits into two surface branches farther east.

Tel Aviv is building a subway-surface line from scratch, without any branching. The Red Line is to run underground in Central Tel Aviv, Ramat Gan, and Bnei Brak, and on the surface farther east in Petah Tikva as well as at the other end in Jaffa and Bat Yam. At the Petah Tikva end, an underground connection to the depot is to enable half the trains to terminate and go out of service without running on the surface; at the Jaffa/Bat Yam end, a loop near the portal is to enable half the trains to terminate and reverse direction without running on the surface.

The American way works better than the incipient Israeli way. The main advantage of branching is that the greater expanse of land in outer-urban neighborhoods and suburbs means more lines are needed than in the center to guarantee the same coverage. Thus Downtown San Francisco has just one line under Market Street, serving not just Muni Metro but also BART on separate tracks, but in the rest of the city, BART and the five branches of Muni serve an arc of neighborhoods from the Mission to the Sunset. The lack of branching on the Tel Aviv Red Lines means that it will not be able to serve Petah Tikva well: the city is not very dense or very central and has no hope of getting the multiline crisscross pattern eventually planned for Central Tel Aviv.

One implication of the fact that subway-surface lines should branch is that they are more appropriate for cities with natural branching than for cities without. Boston in particular is an excellent place for such branching. Its street network does not form a grid, but instead has arterials that are oriented around the historic city center; the Green Line makes use of two such streets, Commonwealth Avenue hosting the B branch and Beacon Avenue hosting the C branch. A light rail line following Washington Street could likewise branch to Warren Street and Blue Hill Avenue and potentially even branch farther out on Talbot Avenue to Ashmont, effectively railstituting the area’s busiest buses.

In contrast, cities whose street networks don’t lend themselves well to branching should probably not build subway-surface lines. North American cities with gridded street networks have little reason to use this technology. If they are willing to build downtown tunnels and have the odd right-of-way running toward city center diagonally to the grid, they should go ahead and build full rapid transit, as Chicago did on the Blue Line of the L.

Speed and range

Tramways are the cheapest variety of urban rail and metro tunnels are the most expensive. The reason cities don’t just build tramways in lieu of any grade separation is that tramways are slow and therefore have limited range. Berlin’s tramways average around 16 km/h; they run partly in mixed traffic, but I don’t think they can cross 20 km/h even with dedicated lanes and signal priority.

What this means is that tramways are mainly a solution for city centers and near-center neighborhoods. The tramways in Berlin work okay within the Ring, especially in U-Bahn deserts like the segment of East Berlin between U2 and U5. But in suburban Paris, they’re too slow to provide the full trip and instead work as Metro and RER feeders, providing circumferential service whereas the faster modes provide radial rail transport.

Tramway-centric transit cities can work, but only in a constrained set of circumstances:

  • They must be fairly small, like Karlsruhe, Strasbourg, or Geneva.
  • They should have a network of sufficiently wide streets (minimum 20-25 meters including sidewalks, ideally 30-35) through city center as well as radiating out of it.
  • They should have a supplementary regional rail network for longer trips.

Tramway-and-regional-rail is a powerful combination. Zurich is based on it, having rejected a subway network in two separate referendums. However, once the city grows beyond the size class of Strasbourg, the regional rail component begins to dominate, as there are extensive suburbs that are just too far away from city center for streetcars.

Upgrading to rapid transit

It’s common for cities to replace light rail with rapid transit by building new tunnels and burying the tracks. Historically, Boston and San Francisco both built their subway-surface networks by incrementally putting segments in tunnel, which would later protect these lines from replacement by diesel buses. Stockholm and Brussels both incrementally upgraded streetcars to metro standards, calling the intermediate phase pre-metro. Karlsruhe is building a tunnel for its Stadtbahn.

However, in the modern era, not all such tunneling projects are equally useful. Subway-surface lines stay subway-surface indefinitely: they have so much surface branching that the cost of putting everything underground would be prohibitive. San Francisco activists have flirted with a plan to replace one Muni Metro surface line with rapid transit and then reduce the rest to tramways with forced transfers; this plan is both terrible and unlikely to happen. Tel Aviv might eventually come to its senses and bury the entire Red Line, but this is possible only because the current branch-free layout is already more suited for a subway than for a subway-surface system.

Tram-trains are easier to convert to rapid transit. All that’s needed is a short tunnel segment in city center. Thus, in addition to the Karlsruhe tunnel project, there are serious discussions of city center tunneling in a variety of North American cities, including Portland and Calgary (in the near term) as well San Diego (on the 2050 horizon).

Finally, tramways can be upgraded to full rapid transit more easily than to either of the two intermediate forms. A good tramway is rarely a good subway-surface system, because the subway-surface system ideally branches and the pure tramway ideally does not. Moreover, a good tramway is unlikely to go very far into the suburbs because of its low speed, whereas a tram-train’s ability to leverage high speed in train mode allows it to go deep into the suburbs of Karlsruhe, Calgary, or San Diego. The optimal place for a tramway – dense city neighborhoods following a single line – is also the optimal one for a metro line, making the upgrade more attractive than upgrading the tramway to a hybrid.

What Berlin is Building is Not What It Needs to Build

Berlin has a deceptively simple S-Bahn network. There’s the Ringbahn circling city center. There’s the elevated east-west Stadtbahn, which has two tracks dedicated to S-Bahn service and two for everything else, including longer-range regional trains and intercity trains. And there’s the two-track North-South Tunnel, which only carries S-Bahn traffic; longer-range traffic uses the four-track north-south mainline through Berlin Hauptbahnhof, whereas the North-South Tunnel intersects the Stadtbahn one station east of Hauptbahnhof, at Friedrichstrasse.

The main S-Bahn capacity needs in Berlin are east-west; meanwhile, the North-South mainline is underfull, with Wikipedia listing around 7 trains per hour. And yet, Berlin’s big S-Bahn capital project is a new tunnel, dubbed S21, adding yet another north-south track pair through Hauptbahnhof. Fortunately, the project is salvageable, but only if the city and the federal government act quickly, within a few years, to change yet-unbuilt phases to run in the right direction.

Berlin urban rail traffic map

Here is a map of traffic demand on every interstation on the combined Berlin U- and S-Bahn network (source, p. 6):

The numbers are in thousands of passengers per weekday in both directions combined.

The U-Bahn is in blue. It’s a weird-looking network because two lines (U7, running northwest-southeast in the west, and U9, running north-south also in the west) were built in the Cold War to serve West Berlin’s center around Kurfürstendamm, whereas the S-Bahn and the older U-Bahn lines serve the historic center. Since reunification, Germany has made an effort to move the Berlin central business district back to the historic center, and S21 is to reinforce that, serving the western end of Mitte.

Unfortunately, as we see in the green lines, that’s not where the pressing S-Bahn capacity needs are. First, the Stadtbahn is busier than the North-South Tunnel. Second, the busiest branches heading into the city come from the east, with substantially more traffic than from the north and south.

And then there’s the Görlitz Railway. It is the line heading to the southeast, without its own trunk line through the city – it reverse-branches to the two directions of the Ringbahn. Moreover, going north there’s additional reverse-branching, to the Stadtbahn (S9) and around the Ring to the northern branches (S8, S85), with each service running only every 20 minutes. Total traffic across these services is quite high, 107,000 weekday passengers, compared with 144,000 on the Prussian Eastern Railway (S5, S7, S75; S5 is the mainline), 128,000 between the two branches feeding the North-South Tunnel from the south, and 133,000 between the two branches feeding the North-South Tunnel from the north. The brief segment where S9 runs alongside the Ring has 184,000 weekday passengers, the city’s busiest.

S21: what Berlin is actually building

Berlin Hauptbahnhof is a new station. It only opened in 2006, when the North-South Intercity Line opened. The new four-track line has ample capacity for additional S-Bahn traffic, but nonetheless it hosts no S-Bahn trains in regular service. Instead, there are plans for two additional S-Bahn tracks, mostly in tunnel, parallel to the line, with service to Hauptbahnhof:

The map does not show the phasing. The segment from the Ringbahn in the north down to Hauptbahnhof is just about complete, with opening expected soon. The segment from Hauptbahnhof to Potsdamer Platz, which contrary to the map is to be nonstop, is in early stages of construction, and Wikipedia says it is expected to open in 2023.

Farther south of Potsdamer Platz is still not under construction, and frankly should not be built as is. The only real addition this would give to the network is the stop at Gleisdreieck, where the line intersects the east-west U1; the North-South Tunnel intersects U1 without a connection, the only place in the city where there is a missed U-Bahn/S-Bahn connection unless one counts the marginal U9/Stadtbahn miss in which the next station, Zoologischer Garten, is a transfer.

However, the North-South Main Line’s tunnel portal lies just south of Gleisdreieck, and thus it should be feasible if nontrivial to add platforms there for two of the tracks. Farther south, at Yorckstrasse, it is well outside the portal and adding platforms should be fairly easy.

Görlitz Railway S-Bahn: what Berlin should be building

A radial rail network with three lines should aim to have them meet at a triangle in city center. Berlin has two S-Bahn radial lines, and S21 is to add a third. Instead of running parallel to the North-South Tunnel, it should provide a third trunk line. North of Potsdamer Platz the route is already baked in, but farther south, the Görlitz Railway route is a perfect legacy line to link to. It is quite busy, and the likely locations of the intermediate stops between existing infrastructure and Potsdamer Platz are busy U-Bahn stations in their own right.

I was delighted to see this already discussed on the technical transit blog Zukunft Mobilität. It has a long list of potential Berlin rail extensions, some in accordance with current long-term plans, some not. It specifically criticizes S21 for duplicating existing infrastructure, and proposes an extension to the southeast, mentioning that there were plans to that effect in the 1930s. There are two variants, one through Hermannplatz and one through the old route of the Görlitz Railway.

A higher-zoom 11 MB image is available here.

The dashed lines denote under-construction lines, including S21 to Potsdamer Platz, the 4.5-kilometer Siemens Railway to the northwest, and the U5-U55 connection. Dotted lines denote lines I am proposing: either variant connecting S21 toward the southeast, paired with the Siemens Railway as well as two new-build lines through the area of Tegel Airport, which is slated for redevelopment after the Berlin-Brandenburg Airport finally opens. Two branches are depicted toward Tegel, one toward airport grounds to be redeveloped, and one going farther north taking over S25; there are already discussions of a rapid transit line to Tegel, branching off of U6, but this option does not force the outer parts of U6 to contend with reduced frequency.

The two branches should of course not both be built. The main advantage of the southern option is that it hits Hermannplatz, one of the busiest stations in the system: the above diagram of rail ridership shows a large change in U8 demand north and south of the station, and a factsheet from 2010 asserts that it is the second busiest U-Bahn station, closely behind Alexanderplatz. In effect, it functions as an express link from Neukölln to city center. U8 isn’t especially crowded – nothing in Berlin is – but it’s busiest than the North-South Tunnel; this link is at least as justified as the S21 tunnel to the south. This would require about 7 km of tunnel. While S-Bahn tunnels cost more than U-Bahn tunnels, this is deliberately an express line, so keeping costs down to the per-km level of the U5-U55 connection (525 million for 2.2 km) is reasonable, making it a 1.8 billion project or thereabout.

The northern option works differently. It doesn’t hit anything as interesting as Hermannplatz on the way, but it does serve Alt-Treptow, one of the bigger rapid transit deserts inside the Ring. The infill station would also break what is the second or third longest interstation on the Ring. Closer in, it has better coverage in the center – Checkpoint Charlie offers another CBD station in addition to Potsdamer Platz. The cost is more of an open question here. From Görlitzer Bahnhof to Potsdamer Platz it’s about 4 km; east of Görlitzer Bahnhof it’s plausible that the line could reuse the Görlitz Railway’s right-of-way and run elevated, or at worst underground with cut-and-cover. However, the per km cost of the tunnel would be higher, since proportionately more of it is in city center, and it has the same number of stations over shorter length; my vague guess is somewhat less than 1.5 billion.

The Berlin S-Bahn would become a system with three radial lines, meeting at Hauptbahnhof, Friedrichstrasse, and Potsdamer Platz. All reverse-branching would cease: the various branches on the Görlitz Railway, including the existing ones as well as an under-construction one to the airport-to-be, would feed into the S-Bahn trunk, rather than to the Ring or the Stadtbahn. The removal of S25 from the North-South Tunnel would create space for the S8 and S85 services in Pankow to use the North-South Tunnel instead of diverting to the Ring and Görlitz Railway. Potentially, the North-South Tunnel could also be realigned to serve Gleisdreieck, as depicted on the map. Finally, with S9 removed from the Stadtbahn, there would be room to beef up service on S3 and/or end the current practice in which S75 trains from the east stop at Ostbahnhof rather than running through.

Germany isn’t perfect

Writing about North America, I talk a lot about how it can Germanize its regional rail network. But it’s important to understand that while far better than North America, Germany is not perfect. It makes mistakes of many kinds: some involving high construction costs, some involving schedule slips, some involving unnecessary prestige projects. These can mostly be prefaced by “by Continental standards,” though the Berlin-Brandenburg Airport disaster is bad even by the standards of the Anglosphere and its billion-dollars-per-kilometer subways.

The Berlin S-Bahn is a case in point. It has a pretty hefty peak-to-base ratio by German standards – the Ring lines (S41 and S42) run every 5 minutes peak and every 10 off-peak, and a number of other lines have a peak-to-base ratio of 2 as well. It also has a peculiarity in that S75 trains only run east of Ostbahnhof; I can’t tell if there’s a problem with track capacity or demand mismatch, but if it’s the former then it’s strange since peak S-Bahn traffic on the Stadtbahn is only 18 trains per hour (Munich achieves 30 through its central tunnel, with much higher crowding levels), and if it’s the latter then it’s again strange – why not run through to Westkreuz like S5?

S21 is another of these little mistakes. It’s a prestige project on the heels of the construction of Hauptbahnhof, rather than a solution to a transportation need. There are six north-south tracks through Berlin between the S-Bahn and the mainline and they’re not anywhere near capacity; the mind boggles at why anyone would add seventh and eighth tracks before adding fifth and sixth east-west tracks.

Fortunately, the mistake is fixable. Germany’s dragging infrastructure timeline means that there’s often room for modifications to make things more useful. The airport is a lost cause, but S21 is not. From Potsdamer Platz south there’s a good option that adds S-Bahn service exactly where it is needed and simplifies citywide schedules by making it feasible to eliminate reverse-branching. In lieu of building more autobahns, Berlin should commit to building the southeastern extension via Alt-Treptow or Neukölln.

The Boundary Between the Transit City and Auto-Oriented Suburbia

Public transportation use is higher in cities than in suburbs. Cities with stronger transit networks have larger transit-rich, auto-hostile cores, and some have good transit in lower-density suburbs, but ultimately the transit city has a limited radius, beyond which automobiles dominate. Successful examples of suburban transit, like Zurich, just keep the city-suburb gradient shallower than in other transit cities.

The most fascinating aspect of this is the boundary between the transit-oriented city and the auto-oriented suburbs. Uniquely in the metro area, the boundary region has good access by car as well as by transit, making it ideal for uses that want to interface with both modes of transportation. This specifically includes bus stations, stadiums, and big box retail, as well as more sporadic meeting points between urban and suburban residents.

Where the boundary is

Because the boundary zone is defined by good transit as well as highway access, it may not be the literal boundary as defined by modal split, car ownership, or any other metric of transportation usage. It can be the outer end of some rail line extending into the suburbs, and in that case it may be a salient into auto-oriented territory. There are a number of examples in the United States, where the postwar rapid transit projects have not been accompanied by much transit-oriented development, and thus their outer stations are in low-density suburbs where transit service functions as expensive S-Bahns. BART and most of the Washington Metro are like this, as are the suburban lines of the Boston subway.

For example, here is Newton Centre, on the Green Line D branch:

The light rail station is just to the left (south) of the street. This is a walkable suburban street with a train that comes pretty frequently all day, and yet the dominant mode of transportation here is clearly cars, as one can see in the parking lot to the left. Transit usage here is similar to the metro area’s average – Newton averages 11.9%, the Boston metro area 13.4% – but this says more about the rest of metro Boston than about Newton Centre. Nonetheless, such a location is convenient to access from the city if one lives near the Green Line, and is also reasonable convenient by car, as it is just 4 km from the freeway, and the majority of the distance is along the fast arterial that is Route 9.

The importance of highway access also works in reverse. In cities with strong transit networks and weak motorway network, there may be a freeway salient into the city, creating a zone that is car-friendlier than the rest. If it also has ample parking, which it usually does, then it will end up creating a boundary within an area that is on most metrics transit-oriented.

In London, the urban renewal zones around Stratford and Canary Wharf are examples – the city is unusually poor in freeway infrastructure, but two of the few radial motorways hit these two business districts. Here is Stratford:

The built-up density is high, and Stratford is one of the busiest Underground stations. But the roads are big for the city they’re in and there are large surface parking lots all over.

I’m deliberately including two examples with very different urban layouts and actual transit usage levels to hammer home the point that the boundary is defined merely by the existence of supportive infrastructure for both cars and public transit.

Can the entire city be friendly to both cars and public transit?

No.

There are several reasons for this. The first and most fundamental is that public transit is only successful if it can leverage scale. The adage frequency is freedom comes from this fact, but the same can be said about related issues of span, reach, and network effects. This is why frequency-ridership spirals are so dangerous – a small cut in service can lead to a much greater reduction in ridership.

The second reason is that drivers prefer a different urban layout from transit users, cyclists, and pedestrians. Cars are space-intensive on the road as well as on the parking lot, but can achieve high average speed if there’s no traffic, so they end up preferring spread-out development. Public and active transport are space-efficient but involve a lot of slow walking, so they prefer dense development at distinguished nodes with train stations, featuring strong commercial city centers with high job concentration. The boundary zone I speak of must be underlain by a strong enough transit network in the city core that people will fill the trains at all hours of day.

Concretely, neither the example of Newton nor that of Stratford can work citywide. Newton cannot work citywide because if every residential metro station is a parking lot, then nobody will ride the trains off-peak, and the city will de facto be exclusively auto-oriented as a result. Two years ago I compared the proportion of boardings at suburban stations that occur in the morning peak in New York (67% LIRR, 69% Metro-North) and Paris (46% on the SNCF network). Well, I would later find data for the Washington Metro, which has high off-peak frequency like the RER but low-density parking lot stations like the LIRR and Metro-North, and the proportion of riders in the morning peak is much closer to that of the LIRR than to that of the RER.

Likewise, Stratford can’t work citywide, because most of the city is not a reclaimed railyard with enormous space for all manners of new development. Building the expansive motorway network that would allow cars to rapidly reach every part of the city would normally require extensive neighborhood demolitions; American cities only managed to do so because to the road builders, destroying working-class (and often black) neighborhoods was a feature rather than a bug. Building a new city with ample road infrastructure is possible without this history, but then one gets Houston, hardly an example of good transit accessibility.

Land use at the boundary

The boundary zone’s unique accessibility by both cars and transit makes it ideally suited for land use that really wants both. Such land use has to have the following features:

  1. It needs to have a large regional draw, or else distinct neighborhood centers, some transit-oriented and some car-oriented, can do better.
  2. It needs to specifically benefit from good highway access, for example for deliveries, but also from good transit access.
  3. It is not so high-value that city center’s better transit access in multiple directions trumps access by transit in one direction and by cars in another.

Sporadic meetings satisfy all three criteria. For one personal example, in 2013 I visited New York and participated in a LARP taking place in a camp somewhere in Massachusetts, accessible only by car; I traveled with friends in the suburbs and we arranged that they would pick me up at Southeast, the northern end of the Metro-North Harlem Line’s electrification, so chosen because of its excellent multidirectional freeway access.

I bring up LARPing because it’s such a small community that it has to draw regionwide – in the case of the one I went to, participants came from all over Eastern New England and even beyond – and thus, anywhere with lower transit usage than New York, must appeal primarily to the driver, not the transit user. Nerdy conventions in general tend to either be enormous, like Comic-Con, or take place in cheap suburban edge city hotels, with meetings for carpools arranged at choice suburban train stations.

More common uses that like the boundary zones include major stadiums and big box retail. Stadiums appeal to a broad section of the population with little differentiation between city residents and suburbanites. They have to have good transit access even in auto-oriented American cities for reasons of capacity, but they also have to have good auto access for the use of drivers; stadiums are land-intensive enough that they can’t locate in city center at all, with its omnidirectional transit access, so instead they must be at the boundary zone. Thus Stratford hosts the London Stadium, the Stade de France is in Saint-Denis with good motorway as well as RER access, and Yankee Stadium is tucked at a corner of the Bronx with two subway lines and good expressway infrastructure.

Big box retail is more complicated – for one, its draw is so local that even a small city can support several Walmarts, Carrefours, and Aldis (Walmart is weak in big cities, but the big European retailers aren’t). Nonetheless, boundary zone stores exist: the big supermarket I’m most familiar with in Boston, Star Market at Porter, is on top of a subway station but also has a large parking lot, while the supermarket I shop at here in Berlin, Kaufland, is a two-story big box next to the Gesundbrunnen U- and S-Bahn station, with the ground floor devoted to parking.

I suspect the reason big box retail likes the boundary zone is that while it is local, there are extensive mixed areas rich in both drivers and non-drivers, where a big store must appeal to both in order to succeed. The Gesundbrunnen area is one of the city’s densest, but car ownership in Berlin is still higher than in Paris or New York. The same is true of the area around Porter Square in Cambridge and Somerville, albeit at lower density and with lower transit usage, so Star Market puts its parking on the surface rather than in a structure.

Bus station siting

The most interesting land use that prefers the boundary zone, and the origin of this post, is the intercity bus station. Here is Herbert in comments:

Can you do a post on the contradictory demands for the site of the main intercity bus station?

On the one hand, it is desirable that it is within easy reach from the highway. On the other hand it should be as close to downtown as possible and also easily reachable by public transit. And last but not least there should of possible be one interchange station for every city for connecting passengers.

It’s almost impossible to find a site that goes all requirements. Berlin ZOB certainly doesn’t…

Whereas train stations have obvious preferred sites – the central business district – bus stations have to balance centrality with highway access. In Paris, this is Gallieni. This station is just outside the city at the end of Metro Line 3, where the Boulevard Peripherique meets the A3 autoroute, which connects to further motorways with good access to the north, south, and east. Like Stade de France, Gallieni is a salient of the auto-oriented suburbs almost into city limits, in inner suburbs with high public transit usage.

In New York, there are a few sites that would work fine, but each points in a different direction, making interchange difficult. Port Authority is excellent for buses going to New Jersey and points west and south, and curbside buses tend to pick up in that general area as well, often near Hudson Yards; this is facilitated by a unique situation in which the Lincoln Tunnel has a dedicated inbound bus lane in the morning peak, which many area transit activists wish existed in both directions all day. Buses to Boston could depart from Yankee Stadium, which also benefits from being just beyond the outer end of subway express service, so that travel speeds to Manhattan are faster. However, in practice they depart from the same curbside location on the Far West Side as the buses to Philadelphia and Washington, frustrating riders who see their bus spend an hour in city traffic.

The situation of New York is unusual in that it is located next to two wide rivers with few crossings, and thus does not have a proper orbital motorway with a location like Gallieni. But New York is not unique in having difficult bus station siting choices. London has the same problem: for one, the M25 orbital is so far out of the city; and perhaps more importantly, British buses are priced cheaper than trains in order to control crowding levels on trains to London, and thus dumping bus passengers on a regional train to Central London would be strictly worse than just letting them ride the train the entire way for a reasonable fare.

The Rhine-Neckar Region

The weekend before last, I visited Kaiserslautern and Mainz; I have photos from Mainz and will blog about it separately later this week. Due to a train cancellation, my 2.5-hour direct train to Kaiserslautern was replaced with a three-leg itinerary via Karlsruhe and Neustadt that took 5.5 hours. Even though neither Kaiserslautern nor Karlsruhe is contained within the region, they are both served by the Rhine-Neckar regional rail network. After riding the trains I looked up the network, and want to explain how things work in a metro area that is not very well-known for how big it is.

How polycentric is the system?

The Rhine-Neckar is polycentric, but only to a limited extent. It does have a single central city in Mannheim, with 300,000 people, plus another 170,000 in Ludwigshafen, a suburb across the Rhine. With Heidelberg (which has 160,000 people) and many surrounding suburbs, the total population of this region is 2.5 million, about comparable to Stockholm, Copenhagen, and Hamburg.

The liminal polycentricity comes from the fact that Mannheim has a distinguished position that no single central city has in the Ruhr or Randstad. However, Heidelberg, Neustadt, Worms, and Speyer are all independent cities, all of which have long histories. It’s not like Paris, where the suburbs were all founded explicitly as new towns – Versailles in the Early Modern era, and the rest (Cergy, La Defense, Evry, Marne-la-Vallee, etc.) in the postwar era.

The rail network has the same liminal characteristic, which is what makes it so interesting. There is an S-Bahn, centered on Mannheim. There are two main trunk lines, S1/2 and S3/4: every numbered line runs on an hourly clockface schedule, and S2 and S4 provide short-turn overlays on the S1 and S3 lines respectively, giving half-hourly service on the combined lines. Some additional lines are not Mannheim-centered: the S33 is circumferential, and the S5/51 are two branches terminating at Heidelberg. Additional lines fanning out of Mannheim are under construction, to be transferred from the RegionalBahn system; already S6 to Mainz is running every half hour, and there are plans for lines going up to S9.

However, it is wrong to view the Rhine-Neckar regional rail network as a Mannheim-centric system the way the RER is Paris-centric and the Berlin S-Bahn is Berlin-centric. The Mannheim-centered S-Bahn lines run alongside a large slew of legacy RegionalBahn lines, which run on hourly clockface schedules. The S3 serves Karlsruhe and the S1 and S2 serve Kaiserslautern, but this is not how I got from Karlsruhe to Kaiserslautern: I took a regional train via Neustadt, running on a more direct route with fewer stops via Wörth and Landau, and transferred to the S1 at Neustadt.

Integrated timed transfers

Kaiserslautern is not really part of the Rhine-Neckar region. It is too far west. However, it is amply connected to the core of the region: it has S1 and S2 rail service (in fact it is the western terminus of the S2), and it has regional trains to Mannheim as well as to other cities within the region. The regional train from Mannheim to Kaiserslautern and points west is timed to leave Neustadt a few minutes ahead of the S1, as it runs on the same line but makes fewer stops.

In addition, all these trains to cities of varying levels of importance have a system of timed transfers. I took this photo while waiting for my delayed train back to Paris:

Other than the S-Bahn east, the trains all leave a few minutes after 8:30, and I saw them all arrive at the station just before 8:30, allowing passengers to interchange across as well as between platforms. Judging by static arrival boards posted at stations, this integrated timed transfer repeats hourly.

Some of the lines depicted on the map serve cities of reasonable size, including Mannheim and Heidelberg, but also Homburg, the western terminus of the S1. Others don’t; Pirmasens is a town of 40,000, and the intermediate towns on the line as it winds through the Palatinate valleys have a few thousand people each. Nonetheless, there is evidently enough demand to run service and participate in the integrated timed transfer plan.

Population density and the scope of the network

As I’ve mentioned above, neither Kaiserslautern nor Karlsruhe is properly part of the Rhine-Neckar. Neither is Mainz, which is within the Frankfurt region. Nonetheless, all are on the Rhine-Neckar S-Bahn, and Kaiserslautern isn’t even an outer terminus – it’s on the way to Homburg.

This is for two reasons. The first is that this is a new S-Bahn network, cobbled together from regional lines that were formally transferred to the S-Bahn for planning purposes. It lacks the features that bigger S-Bahn networks have, like strong urban service. The Rhine-Neckar is about the same size as Hamburg, where the S-Bahn provides 10-minute frequencies to a variety of urban neighborhoods; in contrast, the S1/2 and S3/4 trunk lines in Mannheim aren’t even set up to overlay to exact 15-minute frequencies on the shared segment to Heidelberg.

I’ve talked about the distinction between regional and intercity service in the context of Boston. In Boston I recommend that some lines be run primarily as intercities, with long-range service and fewer stops, such as the Providence and Lowell Lines, both serving independent urban centers with weak inner suburbs on the way, while others be run primarily as locals, with more urban stops, such as the Fairmount-Franklin Line, which has no strong outer anchor but does pass through dense neighborhoods and inner suburbs.

The same distinction can be seen in Germany, all falling under the S-Bahn rubric. Wikipedia has a map of all S-Bahn systems in Germany at once: it can be readily seen that Hamburg, Berlin, Munich, Stuttgart, and Frankfurt have predominantly local systems, while Hannover, Nuremberg, the Rhine-Neckar, and Middle Germany (where the largest city is Leipzig) have predominantly intercity systems that are run as if they were S-Bahns.

The second reason owes to the urban geography of the Rhineland. Paris, Berlin, and Hamburg are all clearly-defined city centers surrounded by rings of suburbs. The Rhineland instead has a variety of smaller urban centers, in which suburb formation often takes the form of people hopping to a nearby independent city and commuting from there. All of these cities have very small contiguous built-up areas relative to the size of their metropolitan regions, and contiguous suburbs like Ludwigshafen are the exception rather than the rule.

Moreover, the background population density in the Rhineland is very high, so the cities are spaced very close together. This enabled the Rhine-Ruhr to form as a polycentric metro area comparable in size to London and Paris without having any core even approaching the importance of Central London or central Paris. The Upper Rhine is not as industrialized as the Ruhr, but has the same interconnected network of cities, stretching from Frankfurt and Wiesbaden up to Karlsruhe. In such a region, it’s unavoidable that commuter lines serving different urban cores will touch, forcing an everywhere-to-everywhere network.

To reinforce the importance of high density, we can look at other areas of high population density. The Netherlands is one obvious example, underlying Randstad and an extremely dense national rail network in which it’s not really possible to separate different regions for planning purposes. England overall is dense as well, but the south is entirely London-centric; however, the same interconnected network of cities typical of the Middle and Upper Rhine exists in Northern England, which not only invented the railway but also maintains a fairly dense rail network and has a variety of connecting services like TransPennine. Finally, the Northeastern United States has commuter rail line on nearly the entire length of the Northeast Corridor, touching in Trenton between New York and Philadelphia, with perennial plans to extend services in Maryland, Connecticut, and Rhode Island to close the remaining gaps.

Swiss lessons

Switzerland has long had a national integrated transfer timetable, overlaying more local S-Bahn trains in the biggest cities. As long as there is more than one node in such a network, it is necessary to ensure travel times between nodes permit trains to make multiple transfers.

This leads to the Swiss slogan, run trains as fast as necessary, not as fast as possible. This means that, in a system based on hourly clockface schedules, the trip times between nodes should be about an hour minus a few minutes to allow for transfer time and schedule recovery. Potentially it’s possible to set up some intermediate nodes to have transfers at half-integer hours rather than integer hours, allowing half-integer hour timed transfers. Switzerland’s main intercity lines run on a half-hourly takt, with timed transfers on the hour every half hour in Zurich, Bern, and Basel, which are connected in a triangle with express trains taking about 53 minutes per leg; additionally, some smaller cities have timed transfers 15 and 45 minutes after the hour.

Germany’s rail network is less modern than Switzerland’s, and the Rhine-Neckar schedule shows it. S-Bahn trains run between Kaiserslautern and Mannheim in a few minutes more than an hour, which is why the S-Bahn train depicted in the photo above does not participate in the hourly pulse. In contrast, the regional express trains take 45 minutes, which allows them to participate in the pulse with a little bit of wasted time at Mannheim. Potentially, the region may want to level these two service patterns into one local pattern with a one-way trip time of about 50 minutes, through speeding up the trains if possible. A speedup would not be easy – the rolling stock is already very powerful, and the line is 64 km and has 16 stations and a curvy western half. Discontinuing service on the S2 to two neighborhood stations in Ludwigshafen, which the S1 already skips, is most likely required for such a hybrid S-Bahn/RegionalExpress service.

However, it’s critical to stress that, while Germany is lagging Switzerland, Austria, the Netherlands, and Sweden, it is not to be treated as some American basket case. The Rhine-Neckar rail network is imperfect and it’s useful to understand how it can improve by learning from comparable examples, but it’s good enough so as to be a model for other systems in polycentric regions, such as New England, the Lehigh Valley, Northern England, and Nord-Pas-de-Calais.

Too Many Branches, Too Few Trunks

A recent discussion on Twitter about the through-running plan offered by ReThinkNYC got me thinking about an aspect American through-running crayonistas neglect on their maps: the branch-to-trunk ratio. It’s so easy to draw many branches converging on one trunk: crayon depicts a map and not a schedule, so the effects on branch frequency and reliability are hard to see.

In contrast with crayonista practice, let us look at the branch-to-trunk ratio on existing through-running commuter networks around the developed world:

Paris

The RER has 5 lines, of which 4 are double-ended and 1 (the E) is single-ended, terminating in the Paris CBD awaiting an extension to the other side. They have the following numbers of branches:

RER A: 3 western branches, 2 eastern branches.
RER B: 2 northern branches, 2 southern branches; on both sides, one of the two branches gets 2/3 of off-peak traffic, with half the trains running local and half running express.
RER C: 3 western branches, 4 eastern branches; one of the eastern branches, which loops around as a circumferential to Versailles, is planned to be closed and downgraded to a tram-train.
RER D: 1 northern branch, 3 southern branches; the map depicts 4 southern branches, but only 3 run through, and the fourth terminates at either Juvisy or Gare de Lyon.
RER E: 2 eastern branches; the ongoing western extension does not branch, but is only planned to run 6 trains per hour at the peak, so some branching may happen in the future.

The RER B and D share tracks between Chatelet-Les Halles and Gare du Nord, but do not share station platforms.

London

Thameslink has 3 southern branches. To the north it doesn’t currently branch, but there is ongoing construction connecting it to more mainlines, and next year it will gain 2 new northern branches, for a total of 3. Crossrail will have 2 eastern branches and 2 western branches. Crossrail 2 is currently planned to have 3 northern branches and 4 southern branches.

Berlin

Berlin has 2 radial trunk routes: the east-west Stadtbahn, and the North-South Tunnel. The Stadtbahn has three S-Bahn routes: S5, S7, S75. The North-South Tunnel also has three: S1, S2, S25. Each of these individual routes combines one branch on each side, except the S75, which short-turns and doesn’t go all the way to the west.

Berlin also has the Ringbahn. The Ringbahn’s situation is more delicate: S41 and S42 run the entire ring (one clockwise, one counterclockwise), but many routes run on subsegments of the ring, with extensive reverse-branching. At two points, three services in addition to the core S41-42 use the Ringbahn: S45, S46, and S47 on the south, and S8, S85, and S9 on the east.

Munich

There is a two-track central tunnel, combining seven distinct branches (S1-8, omitting S5). S1 and S2 further branch in two on the west.

The excessive ratio of branches to trunks has created a serious capacity problem in the central tunnel, leading to plans to build a second tunnel parallel to the existing one. This project has been delayed for over ten years, with mounting construction costs, but is finally planned to begin construction in 2 days, with expected completion date 2026. At more than €500 million per underground kilometer, the second tunnel is the most expensive rail project built outside the Anglosphere; were costs lower, it would have been built already.

Tokyo

The Tokyo rail network is highly branched, and many lines reverse-branch using the subway. However, most core JR East lines have little branching. The three local lines (Yamanote, Chuo-Sobu, Keihin-Tohoku) don’t branch at all. Of the rapid lines, Chuo has two branches, and Tokaido and Yokosuka don’t branch. Moreover, the Chuo branch point, Tachikawa, is 37 km from Tokyo.

The northern and eastern lines branch more, but the effective branch-to-trunk ratio is reduced via reverse-branching. To the east, the Sobu Line has 5 branches, but they only split at Chiba, 39 km east of Tokyo. The Keiyo Line has 3 branches: the Musashino outer ring, and two eastern branches that also host some Sobu Line trains. The services to the north running through to Tokaido via the Tokyo-Ueno Line have 3 branches – the Utsunomiya, Takasaki, and Joban Lines – but some trains terminate at Ueno because there’s no room on the Tokyo-Ueno trunk for them. The services using the Yamanote Freight Line (Saikyo and Shonan-Shinjuku) have 2 southern branches (Yokosuka and Tokaido) and 3 northern ones (Utsunomiya, Takasaki, and a third Saikyo-only branch).

Conversely, all of these lines mix local and express trains on two tracks, with timed overtakes, except for the three non-branching local lines. The upper limit, beyond which JR East only runs local trains, appears to be 19 or 20 trains per hour, and near this limit local trains are consistently delayed 4 minutes at a time for overtakes.

Implications for Through-Running: Boston

In Boston, there are 7 or 8 useful southern branches: Worcester, Providence, Stoughton, Fairmount, the three Old Colony Lines, and Franklin if it’s separate from Fairmount. The Stoughton Line is planned to be extended to New Bedford and Fall River, making 8 or 9 branches, but the intercity character of the extension and the low commute volumes make it possible to treat this as one branch for scheduling purposes. To the north, there are 5 branches today (Fitchburg, Lowell, Haverhill, Newburyport, Rockport), but there are 2 decent candidates for service restoration (Peabody and Woburn).

The North-South Rail Link proposal has four-tracks, so the effective branch-to-trunk ratio is 3.5. It is not hard to run service every 15 minutes peak and every 30 off-peak with this amount of branching, and there’s even room for additional short-turn service on urban lines like Fairmount or inner Worcester and Fitchburg. But this comes from the fact that ultimately, Boston regional rail modernization would create an RER C and not an RER A, using my typology as explained on City Metric and here.

There are several good corridors for an RER A-type service in Boston, but those have had subway extensions instead: the Red Line to Braintree, the Orange Line to Malden, and now the Green Line Extension to Tufts. The remaining corridors could live with double service on an RER C-type service, that is, service every 7.5 minutes at the peak and every 15 off-peak. For this reason, and only for this reason, as many as 4 branches per trunk are acceptable in Boston.

Implications for Through-Running: New York

Let us go back to the original purpose of this discussion: New York through-running crayon. I have previously criticized plans that use the name Crossrail because it sounds modern but only provide a Thameslink or RER C. Independently of other factors, the ReThinkNYC plan has the same issues. It attempts to craft a sleek, modern regional rail system exclusively out of the existing Penn Station access tunnels plus a future tunnel across the Hudson.

Where Boston has about 7 commuter rail branches on each side, New York has 9 on Long Island (10 counting the Central Branch), 6 in Metro-North territory east of the Hudson, and 9 in New Jersey (11 counting the Northern Branch and West Shore Railroad). Moreover, one branch, the Hudson Line, has a reverse branch; where the Keiyo/Sobu reverse-branching in Tokyo and the Grand Central/Penn Station Access reverse-branching on the New Haven Line offer an opportunity to provide more service to a highly-branched line, the Hudson Line is a single line without branches.

The upshot is that even a four-track trunk, like the one proposed by both the RPA’s Crossrail NY/NJ plan and ReThinkNYC, cannot possibly take over all commuter lines. The frequency on each branch would be laughable. This is especially bad on the LIRR, where the branch point is relatively early (at Jamaica). The schedule would be an awkward mix of trains bound for the through-running system, East Side Access, and perhaps Downtown Brooklyn, if the LIRR doesn’t go through with its plan to cut off the Atlantic Branch from through-service and send all LIRR trains to Midtown Manhattan. Schedules would be too dependent between trains to each destination, and reliability would be low. ReThinkNYC makes this problem even worse by trying to shoehorn all of Metro-North, even the Harlem and Hudson Lines, into the same system, with short tunneled connections to the Northeast Corridor.

On the New Jersey side, the situation is easier. This is because two of the key branch points – Rahway and Summit – are pretty far out, respectively 33 and 37 km from Penn Station. The population density on branches farther out is lower, which means a train every 20 or 30 minutes off-peak is not the end of the world.

The big problem is the attempt to link the Erie lines into the same system. This makes too many branches, not to mention that the Secaucus loop between the Erie lines and the Northeast Corridor is circuitous. The original impetus behind my crayon connecting the South Side LIRR at Flatbush with the Erie lines via Lower Manhattan is that the Erie lines point naturally toward Lower Manhattan, and not toward Midtown. But this is also an attempt to keep the branch-to-trunk ratio reasonable.

The first time I drew New York regional rail crayon, I aimed at a coherent-looking system. The Hudson Line reverse-branched, and I was still thinking in terms of peak trains-per-hour count rather than in terms of a consistent frequency, but the inner lines looked like a coherent RER-style network. But the Hoboken-Flatbush tunnel still had 5 branches on the west, and the Morris and Essex-LIRR line, without a dedicated tunnel, had 4 to the east. My more recent crayon drops the West Shore Line, since it has the most freight traffic, leaving 4 branches, of which 1 (Bergen County) can easily be demoted to a shuttle off-peak, keeping base frequency on all branches acceptable without overserving the trunk; by my most recent crayon, there are still 4 branches, but there’s a note suggesting a way to cut this to 3 branches by building a new trunk. Moreover, several branches are reduced to shuttles (Oyster Bay, Waterbury) or circumferential tram-trains (West Hempstead) to avoid overloading the trunks. There’s a method behind the madness: in normal circumstances, there should not be more than 3 branches per double-track trunk.

I am not demanding that the RPA or ReThinkNYC put forth maps with multiple new trunk lines. The current political discussion is about Gateway, which is just 1 trunk line; it’s possible to also include what I call line 3 (i.e. the Empire Connection), which just requires a short realignment of an access track to Penn Station, but the lines to Lower Manhattan still look fanciful. New York has high construction costs, and the main purpose of my maps is to show what is possible at normal construction costs. But it would be useful for the studios to understand issues of frequency, reliability, and network coherence. This means no Secaucus loop, no attempt to build one trunk line covering all or almost all commuter lines, and not too many branches per trunk.

New York is an enormous city. It has 14 subway trunk lines, and many are full all day and overcrowded at rush hour. That, alone, suggests it should have multiple commuter rail trunk lines supplementing the subway at longer-range scale. It’s fine to build one trunk line at a time, as London is doing – these aren’t small projects, and there isn’t always the money for an entire network. But it’s important to resist the temptation to make the one line look more revolutionary than it is.