The declared objective of investing in transportation is to enhance social welfare by generating benefits for the economy. In this chapter we inquire into the nature and magnitude of these benefits by focusing on two major questions: First, what effects should be regarded as actual benefits rather than merely income transfers between parties? Second, how are we to convert these benefits into monetary values for the purpose of the investment’s comparative assessment? The latter question, regarding incorporation of the estimated benefits into the project appraisal process, is dealt with in Chapter 6. Here we deal with the prior question.