Woow Thats lot of oil to burn in 500 Miles. With that amount of oil consumption, you should consistently see Blue Smoke out the Exhaust, and not just the occasional puff of smoke.
What grade of Oil are you using? Try switching to a higher Weight. If for example you have been using 5W-30 then switch to 10W-40 and see what happens. You should also be aware that if most of your driving is in town, then there is the possibility that your oil was contaminated with Moisture and gas. As such, although your car may have already been burning oil even in town, you may not have noticed it as the amount of oil lost was replaced with other contaminants such as the 2 that I mentioned. Therefore your Oil level may have appeared to remain normal.
When you then take the car on the highway, the contaminants are burned off, and it then appears that your oil consumption goes up up dramatically when driving at Highway speeds.
Juts my 2c Worth.
Phil