The selection of the appropriate transportation technology to satisfy travel demand has far reaching implications in terms of its ability to either effectively support economic growth and prosperity, or be a drain on public resources. In this regard, ensuring a high level of infrastructure productivity is of great importance. While the applicability of various transit technologies ranging from standard bus services to bus rapid transit and rapid rail transit is widely understood, the scalability of individual modes is an aspect that requires greater definition to ensure that a particular mode can have its capacity enhanced over a period of time in suitable increments that can conveniently and efficiently accommodate growth and fluctuations in demand. Rapid implementation of scalable infrastructure solutions is of particular importance in developing countries. This paper investigates: how scalable road-based transit systems are; how demand estimation accuracy effects the provision of transit capacity; and how much spare capacity should be provided. It is concluded that road-based modes are scalable within families of system configurations, and that in low growth scenarios the infrastructure productivity of high capacity modes is poor. It is argued that, while an accurate demand estimate is important from a revenue estimation perspective, demand accuracy from an infrastructure sizing perspective is less important, as the capacity of one component can be influenced by the capacity of others. It is contended that the amount of spare capacity provided at the outset, or at key upgrade points, depends upon the mode capacity configuration, its capacity increase increment size and the forecast rate of growth, not necessarily the ultimate demand.
Paper presented at the 34th Annual Southern African Transport Conference 6-9 July 2015 "Working Together to Deliver - Sakha Sonke", CSIR International Convention Centre, Pretoria, South Africa.