The public buses used to get from town to town here in central America are called "chicken buses" by the tourists and expats. They look very much like school buses in the USA and Canada (which is what they did before they made their way to Guatemala i believe!) but are often more brightly coloured (not so much here in Guatemala but more so as you go South). I´m not quite sure why they are called that but here are a few possibilities that spring to mind:
1) The actual presence of chickens.
These buses are usually quite crowded with local folk and their possessions. Their possessions often include food and other produce, and in a country where electricity is far from reliable and refrigerators are expensive luxury items, the meat for food tends to travel around mostly in the "breathing" form. That is to say that it is more or less a default condition that there will be assorted chickens and other live food in the bus and on the roof (either in a sack or just held under someones arm).
2) A game of chicken between you and them.
When you meet one on the road, you are probably about to play the age old game of "chicken" with them. In the case of meeting one coming the other way, this is usually because the bus is larger than you and that more or less means he has right of way. This in turn usually means that the bus will appear around a blind corner hurtling towards you and fully in your lane. You need to make split second decisions about where on the road there will be room for you (if any) and then get immediately into that space or alternately off the road entirely (with all the associated consequences of that!). In the case of catching up to one of these careening amalgamations of machine, humanity and just about everything else, it means you again have a choice:- to either stay behind the monster for many miles of winding road while trying to breath in the impenetrable wake of smog belching from its exhaust, OR, to again play the game of chicken by trying to get past the brute on the tortuously windy mountain roads without getting killed by something coming the other way! Bear in mind that you are trying to see past both the bulk of the bus and the dense cloud of black smoke as well as the fact that the bus is often not in its lane and may well just squeeze you off the road as you are mid way through a passing maneuver in the middle of a blind corner :)
3) The bus driver is playing chicken with his life (as well as everyone elses on the bus). The maintenance programs on public transport here are somewhat "less than one would hope for" and certainly less than the usual Canadian and US standards. Tires, brakes, exhaust pipes, fuel caps, engine tuning etc, are all really just "optional extras" here. When you combine this with the extremely steep countryside, often heavy rain and a "will" to get as many people and their stuff onto the bus to maximize the number of fares collected, you get quite a "disaster cocktail". In very real terms, anyone who gets onto one of these contraptions is again playing chicken with fate. There is no shortage of mountain corners here with a forlorn little set of half a dozen or more little white crosses alongside the road!
For my part, I am taking plenty of chances riding my motorbike on the roads with these and the other hazards, so I felt no real difficulty when I rode the chicken bus to the market in the next town and later took another back home. It was actually sort of relaxing and I was able to look at the scenery rather than having my eyes glued to the road ahead - although I do admit that the view was somewhat obscured by the number of heads between me and the windows ... both people and livestock :)
