Complex sentence: After five years of construction, the tunnel was opened in October 1991by Queen Elizabeth ll, the tunnel initially had an advisory speed limit, but this was dropped in 2007 as accidents were rare in the tunnels.
Split into simpler sentences: After five years of construction, the tunnel was opened in October 1991. It initially had an advisory speed limit, but this was dropped in 2007 as accidents were rare in the tunnels.