The real Straight's last trip ended badly
From the Laurens, Iowa civic website:
The Final Chapter
In July of 1996 Alvin started a mower trip to Idaho. Near the Pine Ridge Indian Reservation in South Dakota, about 400 miles from Laurens, he was found in his pull trailer suffering from dehydration and severe sunburn. He never fully recovered from this, later suffering a stroke. He passed away November 9, 1996 at a Sioux City hospital. He is survived by a brother, five sons and two daughters.
I wonder what influence, if any, this knowledge had on the screenwriters or on Lynch as they shaped "The Straight Story".