Complex sentence: Between September and December 1996, about of roadway in Ohio was closed so the ODOT could stabilize and repave the roadway; the rocks forming the top of an abandoned mine underneath the freeway had become overstressed.
Split into simpler sentences: Between September and December 1996, about of roadway in Ohio was closed so that ODOT could stabilize and repave the roadway. The rocks, which formed the top of an abandoned mine underneath the freeway, had become overstressed.