On July 6 the first RegioCitadis dual-system LRV for the Regionalbahn Kassel network was rolled out by Alstom LHB. Harry Hondius reports from Salzgitter

IN THE BEGINNING, there was the tram. And then came the light rail vehicle. Both knew their place in society - and they never left their proper tracks. But today things are different. Over the past decade, Europe has seen the emergence of a new generation of lightweight passenger vehicle, able to operate flexibly on both tram and heavy rail lines.

Within this broad category, there are several variants. LRVs designed to run primarily on tram tracks and then venture out onto the rail network have come to be categorised as tram-trains. Cities such as Zwickau have adopted the opposite approach, with lightweight trains running into the city centre using a short stretch of tram track. These are logically defined as train-trams. This expression can also be used for LRV derivatives which operate exclusively on railway tracks, such as those ordered by Swiss Federal Railways.

The concept is not new. In the heyday of the US interurbans, between 1926 and 1963, the fabled Chicago, North Shore & Milwaukee ran for 122 km between the two cities in its name. Its cars ran on tram tracks in Milwaukee, over a largely segregated heavy railway on the trunk section, and finished up on the elevated metro tracks in Chicago. The Key System which linked Oakland and San Francisco between 1939 and 1968 displayed similar characteristics.

Europe's introduction to modern tram-train operation came with the opening of the Karlsruhe - Bretten line in 1992. Over the following 12 years, the Karlsruhe network has grown to cover more than 500 km of regional lines. The fleet now totals 121 two-system cars: 35 GT82S vehicles and 86 designated GT8-100D/2SM. In practice, some of these never see tram tracks, operating only on DB routes, such as the two cars shuttling between Hanau and Rüsselsheim. In 1997 Saarbrücken became Germany's second system, and today has 28 cars. Kassel will be the third, with four lines radiating from the city centre to towns around the region.

Further tram-train networks are in prospect in a number of cities, using dual-system operation at 750V DC and 25 kV 50Hz. These include Porto, Mulhouse, Luxembourg and Strasbourg.

A pioneer of train-tram operation is the RER line between Genève and Bellegarde, where six 1·5 kV DC LRVs have operated on SBB and SNCF tracks since 1994. These cars are fitted with a small diesel generator set for empty running to and from their depot under SBB's 15 kV 162/3Hz wires.

In the Netherlands, the Rijn Gouwe railway has been jointly operated since 2003 by conventional NS EMUs and six Bombardier A32 cars using the original 1·5 kV DC supply. And work has started on converting SNCF's Aulny - Bondy line east of Paris from a conventional 25 kV 50Hz railway to LRV operation using 15 Siemens Avantos. In both of these cases, subsequent phases envisage through operation on new sections of tram track.

In Porto plans are taking shape to order 20 Saarbrücken-type cars from Bombardier to run through from a 25 kV electrified suburban railway to the city's part-completed 750V DC light rail network. Luxembourg's ambition is to build a 750V line serving the Kirchberg plateau, which would be linked to Luxembourg Central station via CFL's existing 25 kV electrified North line. A 750V DC only variation is the metre-gauge tram-train connecting the new Alacant light rail network with Altea on the line to Denia (MR04 p19).

Kassel's RegioTram project

Regionalbahn Kassel's Managing Director Reiner Meyfahrt described the plans for the emerging tram-train network in RG 12.02 p779, although at that time the final choice of route through the city centre had not been confirmed. Total investment in the project is put at €100m.

Four lines are envisaged, totalling 138 km, including 6 km of new track, of which 1·6 km will be in the city centre. The 53 km route from Kassel to Obervellmar and Warburg, and the 30 km Kassel - Wilhelmsh