Complex sentence: In 1910, some passenger trains once again began to run beyond Avonmouth Dock, continuing towards on the newly-opened Henbury Loop Line, which allowed goods trains to the docks to avoid the steep Clifton Down Tunnel.
Split into simpler sentences: In 1910, some passenger trains once again began to run beyond Avonmouth Dock, continuing towards on the newly-opened Henbury Loop Line. The loop allowed goods trains to the docks to avoid the steep Clifton Down Tunnel.