Navigation marking is an essential element of inland waterways. The visibility, location, and quality of navigation signs determine navigation conditions. Therefore, this study aimed to identify opportunities to improve navigation safety on inland waterways in Poland. Particular attention was paid to Polish legislation and international regulations in order to identify discrepancies and propose amendments to individual legal acts. These recommendations were preceded by field studies of selected navigation signs, including assessments of their legibility at night and in conditions of limited visibility. On this basis, and drawing on many years of practical experience on navigable waterways in Poland and Western European countries, the authors developed original proposals for the use of navigation signs, including designs for floating navigation signs and bridge clearance signs, as well as concepts for navigation marking plans for selected infrastructure components related to inland waterways. The proposed measures are expected to improve the recognisability and consistency of navigation markings, which may contribute to better operating conditions for inland waterway users, including both professional inland navigation operators (freight and passenger) and individual recreational users.

This study develops a transparent and reproducible multi-criteria decision analysis (MCDA) framework for selecting the material and structural variant of floating navigation buoys on inland waterways. The decision problem was defined at the buoy-platform level and separated from external descriptive evidence on visual and radar performance. Three alternatives—galvanized steel, rotationally moulded polyethylene (PE), and mixed steel–PE—were assessed using the Weighted Sum Model (WSM) across eight non-overlapping technical, economic, and operational criteria. An eight-member purposive technical calibration panel screened the criteria, agreed their ordinal priority ranking, and validated the performance-class definitions—this panel was separate from a survey of 52 employees responsible for waterway maintenance. Technical performance classes were assigned from post-season condition assessments of 20 buoys per variant, whereas 36 repeated visual and radar observation series were treated as external descriptive evidence. In the baseline rank-sum model, steel buoys achieved 66.11 points, compared with 59.44 for PE and 54.44 for mixed buoys. Alternative rank-reciprocal and rank-order-centroid weight transformations retained steel as the highest-scoring alternative, while equal weights produced a tie between steel and PE (65.00 points each). One-factor sensitivity analysis showed that PE was preferred when the durability weight decreased from 22.22% to approximately 6.7% or when the corrosion-resistance weight increased from 19.44% to approximately 31%. Simultaneous perturbation of all weights retained steel as the highest-scoring alternative in 99.94% of simulations for ±30% perturbations and 95.17% for ±50%. The survey nevertheless showed greater practitioner preference for plastic or mixed solutions. The framework therefore provides an auditable, context-dependent decision process rather than a universal material recommendation and should be recalibrated and validated for other environmental and operational conditions.