Resting the camera on the dashboard of the car to keep it relatively stable would be a good approach. Then it's just the car's movement and the cars outside that will create the blur and not camera shake. This will have to be experimental as far as shutter speeds and exposure are concerned. Obviously night time would work best if I am going to record light streaks. The camera pointing at back seat and kids with blur outside?
Oh, I LOVE how the photographer captured these colors! Almost looks like an oil painting from far away. Rain on the window pane, looking out of the hospital or a car. It doesn't matter the rain was one thing that calmed all the patients.