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.