What are all these roadblocks for anyway?

From FP Passport:

Checkpoints aplenty
Checkpoint and roadblock plagued roads along Mali/Ghana/Burkina Faso/Togo trucking routes

Ever wonder why Africa is so poor? Here’s one reason: In many parts of the continent, it’s hard to ship goods anywhere without paying serious bribes and incurring infuriating delays. Via Felix Salmon comes this very interesting study (pdf) of West African roadblocks (read: places where armed men demand money).