What is auto?

Some articles on auto:

Floridian (train) - History - Amtrak
... Floridian was briefly combined with the Louisville—Sanford run of Auto-Train ... in consists of AT U36B locomotives and purple, red, and white auto carriers mingling with Amtrak platinum mist, red, and blue cars ... the success with the original Lorton—Sanford Auto-Train did not replicate itself on the Louisville-Sanford run, in part due to the poor timekeeping of the Floridian and this train ...