A Method to Determine Supply and Demand indices and Their Equilibrium in Public Transportation Systems

When the demand attains to supply in transportation systems, policy makers are face with a spectrum of solutions with respect to supply and demand management. In such cases, the easiest thing to do may be supply increase, which may be performed by fleet addition. When there are restrictions, such as minimum headway limitation and budget affordability, upgrading the technology, adding supplementary services or applying demand management strategies are the choices. In the absence of sufficient budget, or for a short-term solution alongside technology upgrade, supplementary services may be considered. In such cases, additional optimal capacity should be determined regarding the initial investment costs and rehabilitation costs of both systems. This paper is presented to deal with and improve the public transportation systems, which have a fundamental role in urban transportation. Furthermore, the equilibrium of demand and supply, once supplementary systems and the practical constraints, such as time, costs and technical limitations have been identified, is of great importance. After presenting an overview regarding indices structure and demand and supply index development, Tehran trolley bus is investigated as a case of saturated system. Although the subway system, as the preferred technology, in the mentioned corridor is under construction, the short-term solution is diesel bus addition alongside the trolley bus, because of some limitations in power capacity of the trolley bus lines and available fleet. The present paper presents a method to determine the supplementary fleet regarding the predefined demand and supply indices.