appropriate and general principle is to assume a simplified model
of the track allocation process, taking into account capacity
constraints, demand and supply, and assume the calculated actual
outcome timetables in the do-nothing and in the investment
scenario.In some contexts, assuming socially optimal timetables might
be a reasonable approximation of what society tries to achieve
through regulations, policies, public transport provision, capacity
allocation, pricing, subsidies, etc. In other contexts, profit
maximizing timetables may be a more realistic approximation.
Whatever principle is chosen, a process is needed to system
atically explore the social benefits of different timetables. To do
this, current appraisal and modelling methods have to incorporate
railway capacity analysis from the railway operations research
tradition. At a minimum, one should explore how different
timetables (in the do-nothing and the investment scenario) affect
the total benefits of an investment.
Since the cost-benefit analysis is a simplified representation of
reality, omitting or misrepresenting certain effects to some extent,
the CBA-optimal timetable will not necessarily be the reality-
optimal timetable. But when carrying out appraisals, we are
working under the assumption that the CBA is a sufficiently
accurate representation of reality, in the sense that the CBA-
ranking of investments or policy measure corresponds to the true
ranking. A similar assumption must be made for the evaluation of
timetables. If it turns out that the assumed model of the track
allocation process is clearly unrealistic, this would mean that we
are working with an unrealistic CBA framework, which is not a
sufficiently accurate representation of reality to base judgments or
ranking on.