I love Salcombe in Devon, UK just such a stunning place, as you drive down the hill approaching Salcome you glimpse the sparkling sea through the trees, it looks like the south of France, do go if you can
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?
There are a few things to point out in this picture, first thing, depth of field, this picture makes the mushroom the main focus, whilst the background is blurred. Also, we can see the texture inside of the mushroom. I like this picture the most it is zoomed in, and the texture is smooth.