his vehicle struck mailbox as it was approaching a curve near cartersville .
burns helped found the southern hard rock band in jacksonville , florida .
played on hit songs like sweet home alabama , simple man and free bird .
cartersville is about 125 miles away from macon , where duane allman died .
after 1971 death of allman brothers guitarist , skynrd dedicated free bird .
three other band members were previously killed in a plane crash in 1977 .