Line frequency - Gregory365/TPF2-Timetables GitHub Wiki
Line frequency is the average time between each vehicle on a line.
The frequency can be viewed in the timetable window by selecting: Lines -> [Line name]. It can also be viewed with lower precision in the games line manager, by double clicking on the line.
A line which takes 20 minutes to complete with 4 vehicles on it will have a frequency of 5 minutes. (20 divided by 4 equals 5)