West Germany built the Emsland test facility to prove a technology that felt, for three decades, permanently just about to arrive. Maglev trains float on magnetic fields and touch nothing; the Transrapid was Germany's entry, developed jointly by Siemens and ThyssenKrupp. The track ran 31.8 kilometres from Lathen north to Dörpen, with a turning loop at each end and a depot siding near the southern one, and it was designed for speeds up to 450 km/h.

Because it was a test line rather than a railway, it kept test-line habits. The Transrapid 08 was still on trial runs, but it regularly carried people: engineers, officials, and invited guests who wanted to feel what four hundred kilometres an hour feels like when nothing is touching the ground. It was, quite literally, a ride on the future, and Germany was proud to hand out the tickets.

The maintenance vehicle weighed sixty tonnes and ran on rubber tyres along the top of the concrete beam. The Transrapid left the station at 09:43. At 09:52 the line dispatchers energised the track. At 09:53 the train began to move. At 09:53:57 emergency braking was applied - and roughly half a second and twenty-five metres later, the train reached the maintenance vehicle at 162 km/h.

A maglev has no wheels to lock and no friction brakes to stand on. The Transrapid's low, aerodynamic nose went under the maintenance vehicle, and the vehicle tore the roof off the passenger section as the train drove beneath it. The wreckage carried on for another three hundred metres along the beam before it stopped. Twenty-three people were killed. Eleven survived, ten of them severely hurt.

The guideway runs about four metres above the surrounding farmland, which made the rescue a problem of height before it was anything else. Firefighters arrived with turntable ladders and aerial platforms and worked from the tops of them.

Three people were found only because someone below heard knocking from inside the wreck; crews removed a floor panel and brought them out. Two engineers had been sitting in the rear section, which held its shape better than the front, and lived. Three more were cut free later from what was left of the carriage. The two men from the maintenance vehicle survived because they had been at the far end of it from the impact. Nobody who was on that stretch of guideway escaped unhurt.

The people who died were not commuters on a journey. They were there because somebody had thought they should see this. Among them were staff from the Transrapid programme itself, workers from a local nursing care company, employees of the utility RWE, and visitors from firms associated with the project - the kind of group a proud engineering organisation invites out on a Friday morning. The nursing home staff and the RWE workers were local Emsland people, on an outing to the thing their region was famous for.

Some of the dead had spent their working lives on magnetic levitation. Wu Xiangming, who ran the Shanghai maglev - the only Transrapid system anywhere in commercial service - travelled to the site. So did the German transport minister, Wolfgang Tiefensee, who called the failings major and asked publicly whether the safety measures on the test track had been adequate, and whether they had actually been applied.

Nothing was wrong with the magnets. The maintenance vehicle should have been confirmed clear of the line before the run was released, and it was not. "This accident would not have been possible if all regulations were adhered to," said Rudolf Schwarz of IABG, the company operating the track. Prosecutors pulled the radio transcripts. Two line dispatchers were tried and convicted, one receiving a year and six months and the other a year; both sentences were suspended, the court citing the men's exceptional remorse, their own lasting mental injury, and their retirement. They accepted the verdicts immediately.

A year after the crash a memorial stone was set up at the site, with a steel panel stamped with twenty-three small crosses. The Transrapid never entered passenger service in Germany. The Emsland facility's operating licence expired at the end of 2011 and the line was shut, but demolition has barely begun - the empty concrete guideway still runs north across the fields, four metres up, carrying nothing at all.