The Economical Planning Period for Engineering Works

In certain important situations, the observed nature of the growth of demand for service that must be met by engineering capital works is exponential in form. Plant to meet this demand is provided in instalments, each of which is usually kept in service for a much longer period than that which elapses before the next instalment is required. The problem is, what is the optimum length of the first and subsequent planning periods for various types of plant under different rates of interest and growth? Solutions are presented in this paper. Even though in practical cases the requirements of expediency must be met, it is still helpful to know what is best.