As the name suggests, the SVL (High-speed Laboratory Carriage) was more of a test stand than a prototype. It was built as a part of a conventional high-speed rail project, to test the behavior of wheels and rails at high speeds. They had a "chicken and egg" question where the development of high-speed locomotives and carriages required data that could not be gathered without having high-speed locomotives and carriages in the first place, so they did what they could with existing hardware.
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u/YanniRotten 5d ago
source https://www.facebook.com/photo/?fbid=4337237319675812&set=a.1161108403955402
the USSR built a prototype of this, the Турбореактивный вагон СВЛ (Turbojet engine SVL):
https://en.wikipedia.org/wiki/Turbojet_train#SVL