While St. Frances of Rome never lived to see the invention of the automobile, she is popularly invoked as the patron saint of automobile drivers.
This patronage is connected to a close relationship with an angel, who would constantly envelop her with light.
In The Life of St. Frances of Rome, Georgiana Fullerton explains how she would frequently be illumined by her angel at nighttime.
When she left the oratory, the archangel followed her, and, enveloped in a halo of light, remained always visible to her, though imperceptible to others. The radiance that surrounded him was so dazzling, that she could seldom look upon him with a fixed gaze. At night, and in the most profound darkness, she could always write and read by the light of that supernatural brightness.
With the invention of the automobile, many Catholics would turn to St. Frances and ask for her intercession while they traveled at night, praying that they would receive the same kind of angelic protection.