The Interamericana (Panamerican highway) runs through Costa Rica and is the main entry point into Costa Rica by car.
The border post in the north (to Nicaragua) is called Peñas Blancas and in the south (to Panamá) Paso Canoas.
Costa Rica has lots of unpaved roads and even the paved roads have lots of unpaved sections, potholes and washed out bridges. Do not expect to get anywhere quickly, what looks like a 3 hour journey on the map can turn into 5 or more hours easily.
Be careful, Costa Rica has one of the worst car accident death rates per capita on earth and the locals are appalling drivers!
The government does not seem to place fixing the roads as a high priority. 50km/hr is good over unpaved roads, you hit a resonance frequency where the damping factor of the suspension matches the undulations of the road and you have a smooth ride. Gas stations are full service and they usually take US dollars or Colón(es).Check your change!
There are bus services from the neighboring countries of Panamá and Nicaragua.
Tica Buses run a good service to these countries as well Honduras, El Salvador and Guatemala. There is an extensive network of public bus routes within the country with reasonable fares and usually comfortable seating. If using the bus routes within the country, some ability to speak and understand Spanish is useful. Keep bags on your lap or directly overhead where you can see them.
Interbus and Grayline operate a shuttle bus service between all the major tourist towns in Costa Rica, door to door!
Book shuttle bus or private transfers HERE