Mérida is a city in Mexico.
North/South/West/East towards Chichen-Itza, Valladolid, Cancun, Tulum
To get out of the city to the Periferico & the highway 180, take a San Pedro bus at calle 54 x 67 x 69 just outside San Benito mercado. The cost is 7 pesos (August 2016) & it'll drop right on the highway somewhere around the gas station. There's also a parallel 180D & according to Google maps it's faster for the coast cities but cannot comment on how busy it is, was taken by 180 myself & somehow I believe foreigners on the road to Chichen-Itza would look more logical.
South towards Campeche
To hitchhike south to Campeche and further you can take the bus 60 to the alborada for 7.5 pesos. The bus stops at the corner of calle 62 and calle 69A. This bus will ride on main Merida ring, and you need ask driver to stop near crossroad to Campeche. Next you need walk 150m to start hitchhicking
Going towards Uxmal ruins
There’s a nice option (and also a life hack) how to successfully get from Merida to Uxmal ruins fast with an option of leaving your backpacks in a safe place.
From «Terminal de Autobuses Oriente» take a bus to Yaxcopoil which will take you there for around 20-25 pesos. Once you’ll reach Yaxcopoil, walk towards the highway and hitch-hike to a town called Muna de Arana (you can get there by bus as well, but the ticket price will be a bit higher). Once you’re in Muna de Arana, go to the city centre, get to the main square and find Palacio Municipal.
Palacio Municipal a governmental building, but the best thing about it is that you can ask permission to camp there. Ask the police chief, and once your stay is approved, you will find yourself in a very safe place under surveillance of guards. It will be a wise idea to camp there, wake up early in the morning, leave your backpacks at the police department of Palacio and get a ride with some workers in direction of Uxmal. There are almost no visitors in the morning, so you can enjoy the whole complex of ruins without being bothered by tourists and souvenir-sellers. The entrance ticket costs 213 pesos (July 2016).