Renting a car is highly recommended. Main roads are in good condition and state maps are easily available at any "tourist information kiosk." There are lots of bus routes though the area but most will be slow and crowded. No train service is offered to this State. There is limited air service to outlying communities from Merida.
The fastest route across the region Cancun--Valladolid--Chichen Itza--Merida is the divided four-lane toll road, the cuota Highway 180. The toll between Cancun and Chichen Itza is approximately US$ 30 each way. The road is well-maintained but does not have nighttime lighting; occasional bicyclists and pedestrians create some road hazards, but fewer than on most other Mexican roads. There are few services available along the road--very few gas stations, few vendors or services, etc.--so plan accordingly. Restrooms are available at some toll booth areas.
"Yucatan Today" (http://www.yucatantoday.com) has lot of info and tips online. Pick up a copy of their monthly periodical when in Yucatan for maps, information, and lots of articles.
