The roads on Ambergris Caye are pretty good. They are mostly cobblestone, but they are starting to pave them more and more. They are very decent.
On the back of the island, you will see potholes on the roads that are filled with rainwater etc., but it’s not a problem. They are roads and not paved paths. On the mainland, all the roads are paved, so you don't need a 4-wheel drive.