Complex sentence: During its testing it covered approximately, ending a career that is considered a success, but the train could not be said to have been extensively tested; in three years it covered less distance than the average family car would in that period.
Split into simpler sentences: During its testing it covered approximately, ending a career that is considered a success. But the train could not be said to have been extensively tested; in three years it covered less distance than the average family car would in that period.