Previous work on transportation investments has focused on average impacts in high- and middle-income countries. We estimate average and heterogeneous effects in a poor continent, Africa, using roads and cities data spanning 50 years in 39 countries. Using changes in market access due to distant road construction as a source of exogenous variation, we estimate a 30-year elasticity of city population with respect to market access of about 0.08–0.13. Our results suggest that this elasticity is stronger for small and remote cities, and weaker in politically favored and agriculturally suitable areas. Access to foreign cities besides international ports matters little. Additional evidence points suggestively to rural-to-urban migration as the primary source of this population increase, though we cannot fully rule out natural increase or reallocation across cities.

中文翻译：

---

交通投资的平均和异质效应：来自撒哈拉以南非洲 1960-2010 年的证据

以前关于交通投资的工作主要集中在高收入和中等收入国家的平均影响上。我们使用跨越 50 年的 39 个国家的道路和城市数据估计了非洲贫穷大陆的平均和异质效应。使用由于遥远的道路建设导致的市场准入变化作为外生变化的来源，我们估计城市人口在市场准入方面的 30 年弹性约为 0.08-0.13。我们的研究结果表明，这种弹性对于偏远的小城市更强，而在政治有利和农业适宜的地区则较弱。除国际港口外，进入外国城市无关紧要。其他证据表明，农村到城市的迁移是人口增长的主要来源，