Uncertainty is usually perceived as having negative effects on transportation systems, such as increasing operation cost, decreasing resource utility, and reducing customer satisfaction. However, it is unclear whether this perception is universally true or is true only under certain conditions. This research compares the performance of transportation systems with uncertain parameters with the performance of the same systems in which the uncertain parameters are replaced by their expectations. The analyses prove that uncertainty can have negative, negligible, and positive impact on the performance of transportation systems under different conditions.