I'm considering taking the day train, number 75 diesel railcar, from Don Muang station to Udon Thani. I notice on the timetable that this is the only train going north that does not end in Nong Khai. However, trains going south seem to all leave from Nong Khai. Puzzling. Anyway, it indicates in the timetable that the railway provides a bus to continue on to Nong Khai. Is this in fact correct and does the bus depart from Udon Thani station? Is this bus gratis or does one have to pay additional?