The ADO buses (pronounced: Ah-Deh-O; said quickly) run the most extensive service throughout the whole of Mexico; serving every major city, town and several of the archaeological sites. Tickets can either be booked in advance on their website (which unfortunately doesn’t have an English translation option), or at the booths inside their terminals in Playa Del Carmen and Tulum.
These buses are comfy, air conditioned and will often play a film, which is great for keeping children entertained on the ride. They also run a “Grand Luxury” service along some their major routes outside of the region. Timetables can sometimes be minimal but the arrival and departure times at the destinations ensure that you have an adequate amount of time to fully experience what is on offer there.
They are also relatively cheap, with tickets between Playa Del Carmen and Chichen Itza ranging at around $282 Pesos (18 USD) each way. The buses leave Playa Del Carmen at 8:00 and return from Chichen Itza at 16:00. If you are thinking of using this option for traveling around make sure you leave yourself an adequate amount of time to get to the stop before the departure time as it is more than likely going to be the last bus of the day.
ADO has its own website online . Unfortunately, it is only available in Spanish, but it is not to hard to use as a tool to research times and prices.