Complex sentence: The companies reused the Thames Tunnel, built by Marc and Isambard Kingdom Brunel between 1825 and 1843 for horse-drawn carriages with generous headroom and two carriageways separated by arches, though it was only used by pedestrians.
Split into simpler sentences: The companies reused the Thames Tunnel, built by Marc and Isambard Kingdom Brunel between 1825 and 1843 for horse-drawn carriages. The tunnel hadh generous headroom and two carriageways separated by arches, depite being only used by pedestrians.