Police said Natnicha Daharn, 21, a second-year student of Udon Thani Vocational School, might have not noticed the lowered barrier because the sun would have been in her eyes.
They said her head was nearly severed in the 7.50am mishap on Dong Rai-Ban Phua Road in Tambon Ban Khao.
Witnesses said Natnicha was approaching the level crossing on her motorcycle just as a train arrived and an official manning the site lowered the barrier with its red-and-white sign telling motorists to stop.
The student seemed not to see the barrier and ran into the sling. She was pulled off the bike, which fell at the roadside.