The S-Tog trains that link towns such as Hellerup and Helsingborg north of Copenhagen to the Danish capital look unusual – but it can take a moment to work out why. Each carriage rests on a conventional bogie – the swivelling truck housing most railway rolling stock’s wheels. Scan the eye along the carriages, however, and something is missing. Most carriages rest on one bogie, with the far end supported by a strong swivelling joint that connects it to the next.

The Copenhagen trains, built by a consortium of France’s Alstom and Germany’s Siemens, are among the first of a generation of commuter and regional trains that use articulation – as the sharing of bogies between vehicles is known – to reshape radically the feel of commuter and regional trains. The trains’ interiors resemble one long cylinder, rather than a series of carriages. The individual carriages are shorter but, because there are still two sets of doors on each side, more of the train length is available for passengers to board and alight.