The social benefit of a railway investment cannot be defined
without specifying timetables with and without the investment.
Without an explicit principle for designing these timetables, there
is a risk for arbitrariness, conscious or unconscious strategic
behavior when conducting the appraisal, counter intuitive appraisal outcomes, and a lack of comparability between suggested investments. This applies to all types of railway investments, but
it is especially conspicuous and potentially insidious for capacity
improvements, since the added capacity can be used in several
ways – improved travel times, frequencies or reliability.
The conclusion that the timetables are important is in one
sense almost trivial, but the awareness about the extent of the
issue seems to be limited. Going through research literature and
guidelines for railway appraisal, we have found no more than
mentioning en pass ant of this issue or what principles should
govern the design of timetables. Sometimes it is mentioned that it
is important to have a “good” timetable for the planned investment to make the analysis reveal the highest possible benefit , butnot that the timetable in the do-nothing scenario is equally
important for the analysis, nor any discussion about whether this
“good” timetable is likely to be realized.