Burkina seems to be more efficient about actually building their roads than Ghana. A year ago when I visited Ouagadougou, the road there was completely under construction. This time, from the border to Ouaga was all beautiful, new road. It's been two years and counting, and Ghana has no progress to show for the work they have been doing between Accra and Kumasi, the two largest cities in the country.
To be honest, though, I think the real reason that Burkina's roads are better than Ghana's is that no matter how much you overload a donkey cart, it won't do much to the road.