Justin Bieber -- I'm a Ruff Rider Now

Fresh off of getting a traffic ticket in his Ferrari, Justin Bieber was seen standing up on his $20,000 Ducati today ... buzzing down L.A.'s famous 405 Freeway.

We broke the story ... Bieber bought the bike back in April off a recommendation from his mentor Usher. At the time, JB didn't have a motorcycle license ... and we still don't know if he ever got around to getting one.