Complex sentence: The chord was planned to be the second order after the Stroginsko-Biryulyovskaya one was to be opened in the mid 1990s, however the Soviet Union collapsed before any of those projects could be realised.
Split into simpler sentences: The chord was planned to be the second order after the Stroginsko-Biryulyovskaya one was to be opened in the mid 1990s. However the Soviet Union collapsed before any of those projects could be realised.