I have certainly always known the words in "Old 97" as "Going down grade making 90 miles an hour". Could there be some conflation with the lines in that other wellknown train wreck song, the Carter Family's "The FFV, or The Wreck On The C&O Road": ~~

'Around the bend she darted and against the rocks she smashed
Upside down the engine turned and Georgie's breast was crushed'?

~Michael~