The accident just went down in Alpharetta, Georgia -- law enforcement tells us a passer-by noticed Bobbi's car all smashed up in an embankment and called 911.

When emergency personnel arrived at the scene, Bobbi Kristina was standing next to her vehicle and appeared to be uninjured.

Cops conducted an official accident investigation -- and believe Bobbi Kristina simply lost control of her car while making a left turn out of her apartment complex ... and drove over a curb and down an embankment, striking several small trees along the way.

Eventually, the car came to a stop on a local park trail.

After the investigation, cops issued BK a traffic citation for "failure to maintain lane."