Complex sentence: The park built above the tunnel was named for Hance in January 1991, several months after her death; during her time as Mayor of Phoenix, Hance was a strong proponent of the tunnel and the park.
Split into simpler sentences: The park built above the tunnel was named for Hance in January 1991, several months after her death. During her time as Mayor of Phoenix, Hance was a strong proponent of the tunnel and the park.