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Many cities face the following problem. They have railway lines that go where people live. But these railway lines end at the edge of the city center, and don’t go out the other side.
For cities with this problem, the solution is through running. Terminating a train and turning it around takes a lot of space, space that is usually unavailable in a city center. This means running a railway line through the city often doubles or triples the number of trains it can handle. As a bonus, passengers who are going from one side of the city to the other can do that much more quickly, with no change.
Many cities, such as London, Paris, Munich and Milan, have used through running to turn some of their existing Victorian railway lines into metro-style services, by building tunnels under the city center. A few other cities, like Berlin, built viaducts (bridges that carry roads and railways over obstacles), while others, such as Cologne, have simply added platforms at their main stations to enable suburban trains to run through. But all of these are big cities, with over a million people, where the property value uplift or extra revenues from fares can cover the enormous costs of tunneling. But there is another option, affordable for smaller cities or large towns: the tram-train.
A Karlsruhe tram, running on railway tracks. Image credit: Baden-Wuerttemberg .
Karlsruhe is a small city of only 300,000 people in southwestern Germany, near the French border. The city’s main station is nearly two kilometers from the city center, following a project in the early twentieth century to build a larger station on a less cramped site. This caused great inconvenience to passengers, who had to change to the city’s tram network in order to get to the old center.
In 1957, the city took the first steps towards creating a new type of transit, the tram-train, when it took over a bankrupt suburban railway, the Albtalbahn, and extended it into the city center over the tram network.
Over the next four years the line’s gauge (the space between the rails) was converted from 1,000 millimeters to 1,435 millimeters, the standard gauge used by the tram network, and it was re-electrified at the same voltage as the tramway. The modernization of the line enabled quicker journey times – the 70 minute journey to Bad Herrenalb, the line’s terminus, was reduced to 46 minutes – but more importantly passengers who wanted to get to the city center did not need to change to a tram.
The idea of a tram that runs outside of a city’s urban area was not new: Vienna, for instance, had been operating a similar line to the neighboring spa town of Baden since 1907. Karlsruhe’s inventive step, which came later, was to extend the tram-train onto railway lines that did not just carry tram traffic. In 1979, the line was extended onto a freight railway north of the city, and in 1992 the first tram-train took over pre-existing passenger services, to the town of Bretten.
Joining the tram and train networks together was tricky. German railways are electrified at 15 kilovolts alternating current, while Karlsruhe’s trams use 750 volt direct current, which meant that the city needed to procure trams capable of using both voltages, which were (and still are) rare. The railway and the tram network used two different signaling systems, the ‘traffic lights’ that are used to control the movement of rail traffic. The trams have to use retractable steps to overcome the big gap between the 2.65 meter-wide trams and platforms which can handle 3 meter-wide trains. These steps also enable later models of the trams, whose floors are 570 millimeters above the ground, to work with both 380 and 760 millimeter-high platforms.
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