In Section 2, a simple model is formulated, which captures the main features of applied transport CBA. The model is a simplified version of the current Swedish appraisal practice and guidelines. Section 3 shows, by way of examples, why the social benefits of a railway investment cannot be defined without a principle for choosing timetables before and after the investment, and that this opens the door for both honest confusion and strategic behavior by the analyst. In Section 4, we discuss advantages and disadvantages of different timetable principles, what the (implicit) principles are in current appraisal practice, and what consequences these are likely to have. Section 5 concludes