Complex sentence: Usage continued to decline during the 1990s, reaching its lowest level of around 33 million passengers during 2000/01, since the beginning of the 21st Century, usage has risen and stabilised, fluctuating in a range between 35 and 40 million passengers annually.
Split into simpler sentences: Usage continued to decline during the 1990s, reaching its lowest level of around 33 million passengers during 2000/01. Since the beginning of the 21st Century, usage has risen and stabilised, fluctuating in a range between 35 and 40 million passengers annually.