Set your tripod at the centre of the rear seat and get an angle that can cover the whole wind screen, use ISO100 and set to f/11 or16 subjective to where your are heading, shutter preferable set to B or T, operate by remote.
Do it on the later part of the nite, and plan your route. Avoid busy roads with lots of traffic junction. ( stopping will cause over exposure ). Those with lots of neon signage will be best, but these had got to be drive thro and leaving colourful light trails. Plan some winding roads too and you will get curvy light streaks. Good Luck !
Currently, these light streaks are too bright and lacking in colour.