I drove parts of that route - in and around Merida and then to Celestun and back. My experience was that the general "rules" of driving in the Yucatan applied - watch for topes (and expect that you won't see them all in advance!), try to avoid night driving, make sure you know the norms for signaling turns, etc. - all stuff that was well covered by my guidebooks. I remember driving along a long straight stretch heading west toward Celestun at sunset - hard on the eyes, but gorgeous to see the sun kissing a type of grass with pinkish heads that lined the road - beautiful!

Hope that helps!

We rented a car in Merida and drove to Celestun for the day (and back by dark). No big deal.