You're likely referring to the popular rap song "8 Mile" also known as "Couchtuner" or more officially as "Lose Yourself" but I will provide information on both.

I believe you are referring to a scene in the movie 8 Mile. Near the end of the movie, there is a memorable scene where Eminem (playing a character named B-Rabbit) raps on a parked car near a freeway and after defeating the main competitor he raps standing in a road.

The song's success can be attributed to its intense, motivational lyrics and powerful delivery. "Lose Yourself" is widely regarded as one of Eminem's best songs and a highlight of his career.

If there is any more information you'd like on either of these two topics I will try to provide.