Transport time and cost are decisive factors for shippers when they choose a mode for their transport. For inland waterway transport in particular, these aspects are more uncertain and less easy to generalize than for road and rail. This is due to the highly variable waterway conditions on free-flowing rivers and due to the large variety of inland ships. Today´s transport models, however, do not take these factors into account. This paper shows that dynamic fairway conditions, the ship’s amount of propulsion power, and the captain’s behaviour have a substantial impact on the attainable speed and fuel consumption of inland ships. This in turn has a significant impact on attainable sailing schedules and transportation cost, as we demonstrate through a case study for ships sailing on the Rhine-Danube corridor. We, therefore, conclude that there is a clear potential to improve the representation of inland waterway transport in freight models by modelling the effects of actual ship characteristics and waterway conditions at the micro-level.