Very little known engineering project from early Soviet era -- https://en.wikipedia.org/wiki/Sharopoyezd. Lead by Nikolai Yarmolchuk.

Theoretically,train speeds could achieve 300km/h. Built prototype has been tested only at 70 km/h.

Project was canceled due to high construction and operating costs. There were attempts by Yarmolchuk to revive the project in 50-60s. Although, as well unsuccessful.