Hi Lucas!
Thank you for responding :)
The problem is that the most of the scenes take part in a countryside... There is not much light I could use as an ambient.
Another complication for the shooting on real location is that most of the time the car is going really fast.
Have you ever been trying to use rear projection? Maybe that's a good solution? I could control the speed than and I suppose that when it's in a background, out of focus, it can be convincing... so far I've just done it once, not for a movie, just for "practicing my skills" but it was set in a "city mood" so I could use neon and sodium lamps to imitate.
If you have any good examples of night car scenes from some movies, share them with me...I'll very glad :)
Thank you!
Jakub.