Abstract

Transport infrastructure is deemed to be central to development and consumes a large fraction of the development assistance envelope. Yet there is debate about the economic impact of road projects. This paper proposes an approach to assess the differential development impacts of alternative road construction and prioritize various proposals, using Nigeria as a case study. Recognizing that there is no perfect measure of economic well-being, a variety of outcome metrics are used, including crop revenue, livestock revenue, non-agricultural income, the probability of being multi-dimensionally poor, and local gross domestic product for Nigeria. Although the measure of transport is the most accurate possible, it is still endogenous because of the nonrandom placement of road infrastructure. This endogeneity is addressed using a seemingly novel instrumental variable termed the natural path: the time it would take to walk along the most logical route connecting two points without taking into account other, bias-causing economic benefits. Further, the analysis considers the potential endogeneity from nonrandom placement of households and markets through carefully chosen control variables. It finds that reducing transportation costs in Nigeria will increase crop revenue, non-agricultural income, the wealth index, and local gross domestic product. Livestock sales increase as well, although this finding is less robust. The probability of being multi-dimensionally poor will decrease. The results also cast light on income diversification and structural changes that may arise. These findings are robust to relaxing the exclusion restriction. The paper also demonstrates how to prioritize alternative road programs by comparing the expected development impacts of alternative New Partnership for Africas Development projects. Document type: Book

Abstract

International audience; Aircraft are able to connect any pair of points on earth by using direct routing thanks to the flight management system (FMS) which is the on-board system in charge of the navigation. From an air traffic control point of view, such direct routing is only possible in low density areas. When demand is high, aircraft have to stay on a route network for which crossing points are well located and do not change with time. This location stability, helps controllers to manage efficiently the traffic and ensure a higher capacity compared with management of the same traffic with direct routes for which crossing points always change in space and in time dimensions. This instability reduces the overall capacity of sectors. During the night, when traffic demand decreases, air traffic controllers often deliver direct routes to aircraft because they know that such aircraft will not interfere with other traffic. During the day, such direct route assignments are not proposed anymore and the controller keeps the aircraft on the route network in order to structure the traffic and to reduce the associated complexity. In this research we propose an intermediate milestone for which direct routes could be proposed to aircraft during the day when it is possible and this in order to reduce also the congestion at some points in the airspace. We then consider a real crossing in the French airspace where aircraft have to merge at the same point and exit toward different directions. An optimization algorithm has been developed for this crossing in order to minimize the workload of the controller in charge of this airspace. Three decision variables are then assigned to each aircraft: speed regulation, flight level setting and direct route setting. The associated objectives of this problem are the minimization of the conflict between aircraft (has to reach zero), the maximization of the number of aircraft having a direct route (avoiding the crossing) and the minimization of the flight deviation (speed and FL). When a direct is given to an aircraft, we must ensure that such aircraft is separated from other aircraft by one when they share the same spatial location; this ensure that the controller in charge of such aircraft has few monitoring workload for this aircraft (because it has no interaction with other traffic). This optimization must satisfy some constraints: speed and FL have to stay in a given range. This algorithm has been applied successfully to a test case quite similar to one located in the west of France ACC (Brest) for which the capacity of the crossing point has been strongly increased thanks to many direct routes that have been given.