8:55 AM PT -- The Norman Police Dept. tells TMZ Sports Ross was driving at 9:33 PM when she was struck from behind by a 2000 Mercury Grand Marquis.
Ross was thrown from her Vespa. Both the car and the scooter caught fire.
The driver of the Mercury was a 17-year-old male. He was not injured in the crash.
Officials say the crash is under investigation. WWE legend Jim Ross says his wife was hit while riding her Vespa and suffered multiple skull fractures ... and now he's praying for a miracle.
We spoke with Jim who tells us he's absolutely devastated. He says Jan was riding her Vespa to the gym near their home in Oklahoma when she was struck by another vehicle.
Jim says Jan was not wearing her helmet and struck her head, causing multiple skull fractures. She was rushed to a nearby hospital in critical condition where she underwent surgery.
Jim says the situation is "touch and go" at the moment. Jim says he's "hanging in there. It could be a tough day."
Ross tweeted about the situation, "My wife Jan, my little angel, was hit while riding her Vespa & has multiple skull fractures. She's in surgery now. We need a miracle."
Story developing ...