The second one here are a couple of pages from my new mini-sketchbook. What I do is just move the pen across the page gently and the bumps in the road make the random spikes and shapes. I've just coloured them in back home to make them look more interesting.
I used to do this when I was little travelling in the back of the car. I'd run my finger along the condensation on the window and the bumps and turns in the journey would make my hand fling about allover and make patterns on the windows.