Even if there seems to be an understanding that the timetables determine investment benefits among many practitioner sand in the gray literature, the practice in most railway appraisals is to treat the time table as an exogenous variable outside the analyst's control or responsibility. This is both strange and problematic, since comparability of appraisals of different investments is essential. Forth is reason appraisal guidelines devote substantial efforts to forecast and harmonize assumptions regarding virtually all other variables entering the CBA, from future oil prices and population growth to transit fare sand vehicle operating costs.