For clarity,the model only includes the essentials of a CBA :a
demand function,operator production costs,and a capacity
relationship describing how train running times depend on the
scheduled number of trains and the infrastructure.The nonlinear
demand and linear supply functions,and their parameters,are
taken from Swedish rail guide lines,so they are perfectly realistic
albeit simplified to only one class of travelers. The functional
forms do,however,not matter for the insights of the analysis.
Capacity relationships can be modeled in different ways,depending on the context and the need for details .In one extreme,real,
detailed timetables are constructed,which are then analyzed
graphically or through simulation.In the other extreme,aggregate,
analytically relationships based on the capacity relationships are
used.2 The aggregate approach is usually used for strategic planning and appraisal.We apply the capacity relationshipused by the
Swedish Transport Administration for strategic planning and
appraisal,3 which is similar in structure to the corresponding
capacity relationships used in other countries.This relationship
is defined in Section 2.1. The timetables in the model are
simplified down to the essentials :frequencies and travel times
in a homogeneous time period. Assuming schedule-based time-
tables, rather than frequency-based,would just add complexity to
the exposition without adding further insights.