If you are a tourist, you are legal to drive in Costa Rica under your home country's driver's license during the length of your tourist visa, which usually ranges from 30 to 90 days. Once your visa expires, however, you must apply for a new visa or a Costa Rican driver's license.
Potholes, aggressive driving and windy mountain passes makes driving in Costa Rica challenging. Add in the fact that until very recently, police rarely cracked down on drunken driving unless an intoxicated driver caused an accident.
(Reference 4)
Lawmakers in Costa Rica, hoping to address their country's relatively relaxed stance on drunken driving, began working on new laws in 2008. There have been many revisions, but as of March 2010, it is still legal to consume alcohol in a car, but a blood-alcohol level of 0.75 or higher can get you arrested for driving under the influence of alcohol. By comparison, an adult driving in the US must have a blood-alcohol level of 0.08 to be charged with driving under the influence of alcohol.
A blood-alcohol level of 0.75 or higher -- measured usually be a blood test -- earns you time in jail. The amount of time in jail depends also on other traffic infractions you may be charged with, such as causing an accident, speeding or disobeying a traffic sign. You'll also be fined at least 255,000 colones (almost $455). If you are caught speeding more than 120 kilometers per hour (about 74 miles per hour) and have a blood-alcohol level between.0.5 and 0.75, expect to pay about the same fine. You won't be sent to jail, however.