I shot this in a basement parking lot with my canon g11, (if it was shot in broad daylight it would be a little over exposed,) plus the lighting in the parking lot added a nice effect as you can see
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So while in a passenger's seat, Set your camera to Tv mode ( Or S) and set the shutter speed to 1 second (you could go further but it depends on how still you can remain, but one second seems like the best setting).. and set the lowest ISO setting ( for me it was 80), and the focal length was 6 mm.
Extra Tip: try shooting this image as the car is making a u turn or anything instead of driving in a straight line, it will add more motion in less time, and you will get a nicer effect than straight line.. it all depends on your taste..
Hope you get good results! If i wasnt clear in anything tell me this is my first how i took it post
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PP: levels, and i removed the reflection of my self in the mirror for privacy.