Rail Line Length in an Urban Transportation Corridor

Abstract

The length of a rail line that will minimize total transportation (user and operator) costs, and the threshold demand necessary to ensure that the resulting length of the rail line is nonzero are investigated for an urban transportation corridor. A density of demand for travel to the central business district (CBD) represented by a general function P(x) passengers per unit length of the corridor where x is the distance from the CBD is considered. The line-cost as a function of x, the costs of the rail fleet, rail and bus operating costs and passenger time costs are also considered in the formulation. The fleet size is formulated considering the peaking of demand relative to time. When the line cost is nonuniform there could be several line lengths at which the total transportation cost is minimized or even maximized locally. When the line cost per unit length is uniform, a minimum transport cost rail line of nonzero length exists only if the net gain in travel time and operating cost of transporting the total ridership a unit distance by rail, when compared to bus, exceeds the marginal line and fleet costs per unit length. In either case, the minimum transport cost rail line length can be determined easily. The effects on the line length of shifts in demand are investigated. Closed-form solutions for the line length are obtained for the cases of sectorial and rectangular corridor-sheds with uniformly distributed demand per unit area.