These studies are based on household data for Ethiopia (Chamberlin et al., They observe that the distance to a passable road and the cost of transporting rice significantly decrease the use of fertilizer in rice production. Controlling for soil fertility, they demonstrate that crop yields for the three major staples in Madagascar — rice, maize and cassava — are lower in isolated areas. In other words, reducing travel time to major cities has significant effects on agricultural productivity in sub-Saharan Africa. It has been found that investments in corridors have a limited effect on smallholders and agricultural production. A study of corridors in Mozambique and United Republic of Tanzania suggests that these routes are likely to be “corridors of power” that benefit relatively few, rather than “corridors of plenty", with 90 per cent of smallholders likely to be left out of value chains.