The crash happened at about 8:40 a.m. Monday on I-95 southbound in the area of Churchman's Marsh.
Police say 65-year-old Billy McLaurin was driving a school bus when it was hit from behind by a tractor trailer, driven by 55-year-old Daniel Hogan of Ephrata, Pa.
Then, police say, a car driven by 33-year-old Nakia Brown of New Castle hit the back of the tractor trailer while another school bus, driven by 69-year-old Linda Frazer of Elkton, Md., sideswiped the front of the tractor trailer.
Brown and McLaurin were transported to Christiana Hospital with minor injuries.
Police say they are still working to determine the cause of the crash.
There were no students on the buses.
Police closed the right two lanes of I-95 southbound to clear the scene.
All lanes are now open.