Even in the car, you have to burn away the darkness from the Taken before killing them, so remember to get 'em in the headlights first...
Other than that, it's just a case of keepin' 'em in front of your vehicle and hittin' the accelerator! You shouldn't have too much of a problemwith this, especially on the couple of levels that have quite long night-time driving segments!
You can check your progress in the stats.