A Chicken bus is an old American school bus now being used for public transportation in countries like Guatemala and Nicaragua. They are called a Chicken Bus, because it's not uncommon to find locals transporting a live chicken while riding the bus.
In Nicaragua taking the Chicken Bus is the best way to get from city to city. It's super cheap and during the day it's always safe. Generally the same can be said about Guatemala as well. However in Guatemala City there's a lot of gang activity and it's not a city to mess around in especially once the sun goes down. I recommend taking the tourist van from the Airport to Antigua or where-ever your destination is. That is what most people do.
I would avoid traveling after dark in a Chicken Bus unless you're comfortable with your situation. Avoid the chicken bus when it's a 20 minute three dollar cab ride vs an hour bus ride hitting stop after stop.
Overall get on the Chicken Bus. It's a great experience and you might even feel like you're eight years old again on your way to school!
Here are some recent informative travel posts:
World Travel Report: Costa Rica
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