Are high transport costs holding back development in Africa?

Adam Storeygard, from Brown, is on the job market, and he says yes.

Focusing on countries whose largest, or primate, city is also a port, I find that as the price of oil increases from $25 to $97 (as it did between 2002 and 2008), if city A is 465 kilometers (1 standard deviation) farther away from the primate than initially identical city B, its economy is roughly 6 percent smaller than city B’s at the end of the period. At a differential of 2360 kilometers, the largest in the data, this rises to 32 percent. I then determine that this effect falls disproportionately on cities that are connected to the primate by paved roads, most likely because they are initially more engaged in trade. Cities connected to the primate by unpaved roads appear to be more affected by transport costs to secondary cities.

An argument for more roads for Africa?