Yes indeed. There is reentry
At the first hint of rain they shut down that option to keep the lanes from becoming muddy rivers.
You are allowed to come and go, but if you plan to do that regularly, they prefer you park in the "car corral" just outside the festival entrance. You're not going to want to leave though--there is so much fun to be had!
If you park in the corral (off-site) it is less frowned upon. There are plenty of vendors so no need to leave, plus nothing around to leave for... Middle of country.
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