Cost – benefit analysis and large-scale infrastructure projects: state of the art and challenges

In this paper I review the problems surrounding the use of cost – benefit analysis (CBA) in the appraisal of large-scale infrastructure projects. I define the requirements of a best-practice transport CBA and show the difficulties in achieving these for large-scale projects. The main difficulties discussed are those of forecasting over long time periods, dealing with imperfect competition in transport-using sectors to obtain estimations of wider transport benefits, introducing private finance and appraising network effects. I conclude that CBA can remain a valuable tool as part of the appraisal process but that the inputs to a CBA have to be carefully assessed, and complementary approaches, such as computable general equilibrium modelling, have a useful role to play for very large or network projects.