The influence of passenger weight on rail and metro running times: Theoretical formulation and applications to the case of Line 1 of the Naples metro system (Italy)

Analyses of transport systems require knowledge of the interactions between travel demand and transport system performance. In general, the travel demand depends on transport system performance, and in turn the transport system performance depends on how many users use the same element at the same time. In the literature, rail and metro systems are generally considered uncongested (i.e. performance does not depend on the travel demand) at least as regards train running times. This contribution examines the dependence of train running times on the number of transported users. Indeed, in rail and metro contexts, the weight of carried passengers in the case of a full load has the same order of magnitude as the unloaded train weight. Hence, variation in the maximum traction effort and the motion resistance between a fully loaded and a completely empty condition implies variations in train running times. Moreover, in frequency services, even in the case of constant demand (i.e. rigid demand assumption), the number of users boarding each train depends on the service frequency. Hence, since service frequency depends on the running times through the cycle time, it is possible to identify a fixed-point problem between the number of boarding passengers and train running times. The application to the case of Line 1 of the Naples metro system has shown the extent of these variations and the extension times conditions that allow defining a cycle time independent of demand variability.