CONGESTION THEORY AND TRANSPORT INVESTMENT

Investment in transit facilities necessarily begins by being largely investment in the provision of new routes or new services under conditions of substantial indivisibilities and increasing returns to scale. Under these conditions the usual profitability tests for determining the desirability of specific investments lead generally to under- rather than to over-investment in transit facilities. As investment proceeds, however, larger and larger proportions of transportation investment are made primarily to relieve congestion on existing routes and to expand overall capacity. This paper discusses the investment designed to relieve congestion. For purposes of economic analysis it is useful to distinguish at least six types of congested situations, which are: simple interaction, multiple interaction, bottleneck, triggerneck, network and control, and general density.