I can sense a lot of concern when planning to drive a car in Mexico. My advice is to act humble, smile and try speaking Spanish and don't drive flashy big SUV's. I will be driving soon from Montreal across United States and all Mexico from its USA border in Brownsville along the Bay of Mexico to almost the tip of Yucatan Peninsula to Merida where I have a house in city Historic Center. I will let you know my impressions and give you advice if you want to do the same.
bienvenidos a Merida