It is not easy to travel around Senegal by car. The population of the African country is increasing rapidly, but the roads are not keeping pace. The World Bank would like to know the lines along which new roads would yield the greatest economic returns. Researchers in transport and planning (CEG) have developed a smart way to do this: by analysing a mountain of data from telephone calls. The presence of telephone traffic between certain cities indicates a connection between these locations, and thus the importance of good road connections. With their study, the TU Delft researchers won the D4D Challenge, the Transport Prize in the Data for Development Challenge, conceived by the telecom company Orange.