Complex sentence: Track 2 no longer exists, however, remnants of Track 2 can be seen inside the tunnel from passing trains on Tracks 1 and 3; the former northbound express track is Track 3; and the former northbound local track is Track 4.
Split into simpler sentences: Track 2 no longer exists, however, remnants of Track 2 can be seen inside the tunnel from passing trains on Tracks 1 and 3. The former northbound express track is Track 3, and the former northbound local track is Track 4.