We measure road improvement and road construction on production and inequality in Colombia from 1993 to 2012, taking into account network effects using a market access approach. We found that roads, by changing market access, have an important effect on GDP growth and all the sectors. We also find that GDP increases with distance to the intervention. We address endogeneity in multiple ways. We use exogenous variation based on the likelihood of receiving a road improvement based on pre-colonial (indigenous) roads least-cost cost path counterfactual road networks that use estimated construction costs; we also build alternative market access measures that focus on quasi-random market access changes stemming from exposure to markets of smaller cities. We find that roads concentrate the land close to that infrastructure in fewer hands. Also, roads have an important effect on municipal development indicators. Roads also seem to have important spillover effects on municipalities located at 35km or closer to the intervention.