*3.2. Timetable Variables*

In this cost model, we have assumed that the route and timetable are identical in both directions. A simple way of describing the timetable is shown in Figure 2. It shows a generic timetable description as a curve showing the number of departures per hour from the end stops and its variation during the day. In the diagram we can see that the timetable can be described by seven time-dependent variables and three variables for number of departures per hour. By changing these 10 variable values, the timetable can be altered in our TCO analysis. Since the buses often run into the night, beyond midnight, the calculation uses time values beyond 24 h, as this simplifies the calculations. In Figure 2, the last bus departs from the end stop at 01:00 in the night, and this is coded as 25.0 h in our model.

**Figure 2.** The generic way of describing the timetable which is used in the TCO model.

In addition to the variables in Figure 2, there are also variables to define the layover time needed off-peak (*T*LayoverOffPeak), during peak times (*T*LayoverPeak), and in the evening (*T*LayoverEvening). The layover time is the time between when the bus arrives at the end stop from one trip, and the time it departs for the return trip. The layover time is mainly used as a buffer time so that a delayed incoming bus shall still mostly be able to depart on time on its next trip. The layover time can also provide some breaks for the driver between trips.

Instead of defining different timetables for the different types of days (weekdays, weekends, holidays etc.) the total traffic during a whole year is instead calculated as the defined typical day, multiplied with the number of effective traffic days which give an estimate of the total yearly traffic. In this paper we use *N*TrafficDays = 313.
