I recently covered the Stadtbahn, a mode of rail transportation running as rapid transit (almost always a subway) in city center and as a tramway farther out. The tram-train is the opposite kind of system: it runs as a tramway within the city, but as rapid transit farther out. There’s a Human Transit blog post about this from 2009, describing how it works in Karlsruhe, which invented this kind of service pattern. Jarrett is bearish on the tram-train in most contexts, giving a list of required patterns that he says is uncommon elsewhere. It’s worth revising this question, because while the tram-train is not very useful in an American context, it is in countries with discontinuous built-up areas, including Germany and the Netherlands but also Israel. Israeli readers may be especially interested in how this technology fits the rail network away from the Tel Aviv region.
What is a tram-train?
Let’s dredge the 2*2 table from the Stadtbahn post:
|Slow in center||Fast in center|
|Slow in outlying areas||Tramway||Stadtbahn|
|Fast in outlying areas||Tram-train||Rapid transit|
The terms fast and slow are again relative to general traffic. The Paris Métro averages 25 km/h, less than some mixed-traffic buses in small cities, but it still counts as fast because the speed in destinations accessed per hour is very high.
Be aware that I am using the terms Stadtbahn and tram-train to denote two different things, but in Karlsruhe the system is locally called Stadtbahn. German cities use the term Stadtbahn to mean “a tramway that doesn’t suck,” much as American cities call a dazzling variety of distinct things light rail, including lines in all four cells of the above table. Nonetheless, in this post I am keeping my terminology distinct, using the advantage of switching between different languages and dialects.
Tram-trains and regional rail
The Karlsruhe model involves trains running on mainline track alongside mainline trains, diverging to dedicated tramway tracks in the city, to connect Karlsruhe Hauptbahnhof with city center around Marktplatz. This also includes lines that do not touch the mainline, like S2, but still run with higher-quality right-of-way separation outside city center; but most lines run on mainline rail part of the way.
North American light rail lines, with the exception of the Boston, Philadelphia, and San Francisco Stadtbahn systems, tend to run as tram-trains, but never have this regional rail tie-in. They run on entirely dedicated tracks, which has two important effects, both negative. First, it increases construction costs. And second, it means that the shape of the network is much more a skeletal tramway map than the more complicated combination of an S-Bahn and a tramway that one sees in Karlsruhe. San Diego has a short segment sharing tracks with freight with time separation, but the shape of the network isn’t any different from that of other American post-1970s light rail systems, and there’s an ongoing extension parallel to a mainline railroad that nonetheless constructs a new right-of-way.
In this sense, the Karlsruhe model can be likened to a cheaper S-Bahn. S-Bahn systems carve new right-of-way under city center to provide through-service whenever the historic city station is a terminus, such as in Frankfurt, Stuttgart, Munich, or German-inspired Philadelphia. They can also build new lines for more expansive service, higher capacity, or a better connection to city center, like the second S-Bahn trunk in Hamburg; Karlsruhe itself is building a combined road and rail tunnel, the Kombilösung, after a generation of at-grade operation. The tram-train is then a way to achieve some of the same desirable attributes but without spending money on a tunnel.
It follows that the tram-train is best when it can run on actual regional rail tracks, with good integration with the mainline system. It is a lower-speed, lower-cost version of a regional rail tunnel, whereas the North American version running on dedicated tracks is a lower-cost version of a subway. Note also that regional rail can be run at different scales, the shorter and higher-frequency end deserving the moniker S-Bahn; the Karlsruhe version is long-range, with S1 and S11 reaching 30 km south of city center and S5 reaching 70 km east.
Where is a tram-train appropriate?
Jarrett’s 2009 post lays down three criteria for when tram-trains work:
- The travel market must be small enough that an S-Bahn tunnel is not justified.
- The destination to be served isn’t right next to the rail mainline.
- The destination to be served away from the mainline is so dominant that it’s worthwhile running at tramway speeds just to get there and there aren’t too many people riding the line beyond it.
The center of Karlsruhe satisfies the second and third criteria. It is borderline for the first – the region has maybe a million people, depending on definitions, and the city proper has 312,000 people; the Kombilösung is only under-construction now and was not built generations ago, unlike S-Bahn tunnels in larger cities like Munich.
Jarrett points out that in the urban world he’s most familiar with, consisting of the United States, Canada, Australia, and New Zealand, it is not common for cities to satisfy these criteria. He does list exceptions, for example Long Beach, where the Blue Line runs in tramway mode before heading into Los Angeles on a mostly grade-separated right-of-way, whereupon it goes back into the surface in Downtown LA before heading into an under-construction tunnel. But overall, this is not common. City centers tend to be near the train station, and in the United States there’s such job sprawl that just serving one downtown destination is not good enough.
That said, the Long Beach example is instructive, because it is not the primary city in its region – Los Angeles is. I went over the issue of outlying S-Bahn tunnels a year ago, specifying some places where they are appropriate in Israel. The tram-train must be a key tool in the planner’s box as a cheaper, lower-capacity, lower-speed version of the same concept, diverging from the mainline in tramway mode in order to serve a secondary center. Karlsruhe itself is a primary urban center – the only time it’s the secondary node is when it connects to Mannheim, and that train doesn’t use the tramway tracks – but a secondary tram-train connection is being built in outlying areas there, namely Heilbronn.
Different models of urban geography
In the American model of urban geography, cities are contiguous blobs. Stare at, for example, Chicago – you’ll see an enormous blob of gray stretching in all directions. Parkland is mostly patches of green in between the gray, or sometimes wedges of green alternating with wedges of gray, the gray following commuter railroads and the green lying in between. Boundaries between municipalities look completely arbitrary on a satellite map.
In the German model of urban geography, it’s different. Look at Cologne, Frankfurt, Mannheim, or Stuttgart – the built-up area is surrounded by green, and then there are various suburban towns with parkland or farmland in between. This goes even beyond the greenbelt around London – there’s real effort at keeping all these municipalities distinct.
I don’t want to give the impression that the United States is the weird one. The contiguous model in the United States is also common in France – Ile-de-France is one contiguous built-up area. That’s how despite being clearly a smaller metropolitan region than London, Paris has the larger contiguous population – see here, WUP 2007, and see also how small the German and Dutch urban areas look on that table. Urban agglomeration in democratic East Asia is contiguous as in the US and France. Canada looks rather American to me too, especially Vancouver, the city both Jarrett and I are the most familiar with, while Toronto has a greenbelt.
This distinction moreover has to be viewed as a spectrum rather than as absolutes. Boston, for example, has some of the German model in it – there’s continuous urbanization with inner suburbs like Cambridge and Newton, but beyond Route 128, there are many small secondary cities with low density between them and the primary center. Conversely, Berlin is mostly American or French; the few suburbs it has outside city limits are mostly contiguous with the city’s built-up area, with the major exception of Potsdam.
The relevance of this distinction is that in the German or Dutch model of urban geography, it’s likely that a railway will pass through a small city rather far from its center, fulfilling the second criterion in Jarrett’s post. Moreover, this model of independent podlike cities means that there is likely to be a significant core, which fulfills the third criterion. The first criterion is fulfilled whenever this is not the center of a large metropolitan area.
It’s not surprising, then, that the Karlsruhe model has spread to the Netherlands. This is not a matter of similarity in transport models: the Netherlands differs from the German-speaking world, for examples it does not have monocentric S-Bahns or S-Bahn tunnels and it builds train stations with bike parking where Germany lets people bring bikes on trains. Nonetheless, the shared model of distinct municipalities makes tram-train technology attractive in South Holland.
Israel and tram-trains
In Israel, there are very few historic railways. A large share of construction is new, and therefore has to either swerve around cities or tunnel to enter them, or in a handful of cases run on elevated alignments. Israel Railways and local NIMBYs have generally preferred swerving.
Moreover, the urban layout in Israel is very podlike. There do exist contiguous areas of adjacent cities; Tel Aviv in particular forms a single blob of gray with Ramat Gan, Givatayim, Bni Brak, Petah Tikva, Bat Yam, and Holon, with a total population of 1.5 million. But for the most part, adjacent cities are buffered with undeveloped areas, and the cities jealously fight to stay this way despite extensive developer pressure.
The final important piece in Israel’s situation is that despite considerable population growth, there is very little rail-adjacent transit-oriented development. The railway was an afterthought until the Ayalon Railway opened in 1993, and even then it took until last decade for mainline rail to be a significant regional mode of transport. The state aggressively builds new pod-towns without any attempt to expand existing towns toward the railway.
The upshot is that all three of Jarrett’s criteria for tram-trains are satisfied in Israel, everywhere except in and around Tel Aviv. Tel Aviv is large enough for a fully grade-separated route, i.e. the already-existing Ayalon Railway. Moreover, because Tel Aviv needs full-size trains, anything that is planned to run through to Tel Aviv, even as far as Netanya and Ashdod, has to be rapid transit, using short tunnels and els to reach city centers where needed. A tram-train through Ashdod may look like a prudent investment, but if the result is that it feeds a 45 meter long light rail vehicle through the Ayalon Railway then it’s a waste of precious capacity.
But Outside Tel Aviv, the case for tram-trains is strong. One of my mutuals on Twitter brings up the Beer Sheva region as an example. The mainline going north has a station called Lehavim-Rahat, vaguely tangent to Lehavim, a ways away from Rahat. It could get two tramway branches, one diverging to the built-up area of Lehavim, a small suburb that is one of Israel’s richest municipalities, and the other to Rahat, one of Israel’s poorest. There are also interesting options of divergence going south and east, but they suffer from being so far from the mainline the network would look scarcely different from an ordinary tramway.
Beer Sheva itself would benefit from tramways with train through-service as well. The commercial center of the city is close to the train station, but the university and the hospital aren’t, and are not even that close to the subsidiary Beer Sheva North station. The station is also awkwardly off-center, lying southeast of the city’s geographic center, which means that feeding buses into it with timed transfers screws internal connections. So tramway tracks on Rager Boulevard, cutting off Beer Sheva North for regional trains, would do a lot to improve regional connectivity in Beer Sheva; intercity trains should naturally keep using the existing line.
In the North, there are similar examples. Haifa is not going to need the capacity of full-size trains anytime soon, which makes the case for various branches diverging into smaller cities to provide closer service in tramway mode strong. Unlike in Beer Sheva, the case for doing so in the primary center is weak. Haifa’s topography is the stuff of nightmares, up a steep hill with switchback streets. The mainline already serves the Lower City well, and climbing the hill is not possible.
This creates an interesting situation, in which the technology of the tram-train in the North can be used to serve secondary cities like Kiryat Ata and Tirat Carmel and maybe enter the Old City of Acre, but the operational pattern is really that of a Stadtbahn – fast through Haifa and up most of the Krayot, slow through smaller suburbs.