A better option might using a service like UStream. Download their app, set your channel to private, and when you drive places, start your broadcast. I believe they automatically archive anything you livestream, so if something happens and the phone is destroyed, there's still a record of what happened. And it wouldn't fill up local storage.
With an Android phone, this might even be scriptable using something like Tasker. Set it up to automatically start the streaming application as soon as the GPS records you travelling a speed over a certain limit, say 10 mph/20 kph.
I did use an app called iOnRoad they even sent me a free windshield mount for my phone. It doesn't record video but will take a picture when it's senses some danger such as a sudden stop i.e. trying to avoid the car in front of you stopping.
I thought about UStream but I am lucky to get a signal even here in the capital city; GPS or cell.
Maybe a RaspberryPi, a small webcam and solar panel.
With an Android phone, this might even be scriptable using something like Tasker. Set it up to automatically start the streaming application as soon as the GPS records you travelling a speed over a certain limit, say 10 mph/20 kph.