A National Holidays coach carrying up to 15 passengers left the A19 near Sunderland and ended up in a field.
The driver was the only person to suffer slight injuries in the crash which happened just before the Ryhope turnoff.
Police say they do not know what caused the bus to leave the road at about 1930 GMT on Thursday.
The bus was later recovered from the field. Durham Police have appealed for witnesses to come forward.