500 mile trip - no overnights. Easy. Keep the car in sight when you go into a place to eat/pay for fuel. 99% of the time, no issues if you've cable-locked the bike to the rack in my experience.
If you're worried about the bike bouncing off while driving, then you have issues with securing the bike to the rack itself. Seriously, the bike can bounce off going around the corner if you don't secure it properly.
My method involves velcro strips/straps AND bungees. I use 6 - some people claim it's overkill. They could be right but I've never lost a bike while driving, only a bungee cord or two when I used those instead of the Velcro straps.