Are there any air traffic routes where I have to expect more or more severe turbulences than usual? I once heard that over the Atlantic before the South American coasts there are a lot of turbulences, but is there any statistical reference for that?
Great question, I will try to give at least a partial answer.
Clear Air Turbulence, CAT, is more prominent where there are high mountains. The mountains might direct air up, or suck it down etc. Making the winds normally found at any given altitude mix in such a way that air pockets are born. One example are the Lee waves.
BOAC Flight 911 broke-up in flight in 1966 after experiencing severe lee wave turbulence just downwind of Mount Fuji, Japan.
What might not be so easy to figure out are the Jet Streams. In the jet streams wind has a vastly different speed compared to winds of the surrounding air, transitioning such a barrier in a plane can cause a lot of turbulence. I don't remember exactly how those jet streams work, but I believe there are some areas where they are more or less all the time, and some areas where they are not so frequent. They are formed in areas of high temperature differences.
So I say yes, there are routes with more turbulence than others. However if there are any numbers on that I'm not sure :( As far as I can tell you are simply more likely to encounter CAT in certain areas than others.
The main commercial relevance of the jet streams is in air travel, as flight time can be dramatically affected by either flying with the flow or against the flow of a jet stream. Clear-air turbulence, a potential hazard to aircraft passenger safety, often is found in a jet stream's vicinity.
With this commercial relevance in mind I am not sure if the airlines try to avoid these potential problem areas or if the economic interests are too strong.