A technology selection and design model of a semi-rapid transit line

We present a new optimization model for technology selection and design of a semi-rapid transit line. With respect to previous studies, we improve the synthetic representation of the temporal and spatial variability of demand, and of several operational and design aspects. We apply the model to two scenarios offering comparable performance by commercially available technologies in terms of service, rather than assuming that service quality is strongly associated with technology. The model is validated by comparing some computed performance indices with best practices. We show that planning for a faster technology can be more important than the choice between bus and rail per se, except at very low demand density, and that differences of total cost, sum of passengers' time value and operator's cost, between the technologies are smaller than commonly held across a wide range of higher demands. At high demand density multiple-unit rail offers the most cost-effective way to achieve high capacities under many conditions. A scenario variation analysis shows the relevance of differences between value of time components, the bias of averaging vehicle load ratios when assessing the crowding disutility, the usefulness of a demand index abstracting from some specific parameter choices, and the high impact of the project discount rate.