A new composite indicator has been developed to measure how well short sea shipping connects Greek islands to each other and to the mainland, offering policymakers a transparent tool for assessing territorial cohesion. The framework, applied to 2018 baseline data covering 72 islands, integrates normalized key performance indicators into two core dimensions, connectivity and accessibility, and reveals substantial disparities across the network. The study, published in European Transport Research Review, was conducted by Vasiliki-Maria Perra and Maria Boile and draws on a detailed database of the Greek domestic ferry system.
The researchers built their Island Territorial Cohesion Index following composite indicator guidelines established by the OECD, the European Commission and the Joint Research Centre. The full conceptual framework spans six dimensions grouped under transport policy and development policy, including environmental, technological, governance and socio-economic performance. However, the empirical application in this study focuses only on connectivity and accessibility, the transport-related core that could be operationalized with harmonized short sea shipping service data available for all islands. The remaining dimensions are included to demonstrate extensibility but were not empirically assessed and are left for future research.
Connectivity is measured through four sub-indicators: direct connections, port calls, unique vessels and passenger capacity per itinerary. Accessibility is captured through estimated travelled distance, estimated direct distance, estimated travel time and ticket prices. Data came from the Integrated Database on Short Sea Shipping Network developed by CERTH for the Hellenic Ministry of Maritime Affairs and Insular Policy, which integrates sources including ISKTHEEA, OpenStreetMap and the national statistics authority. Distances were calculated with GIS tools, while travel time was derived from scheduled itineraries.
The results expose striking heterogeneity in supply-side characteristics. Crete ranks highest in direct connections with 23 port-to-port links, reflecting its role as a major inter-island hub, while Megisti and Samothrace each have only one connection. Port calls peak in Evia, which benefits from proximity to the mainland and its gateway function toward the Cyclades and Sporades, whereas Thirasia records the fewest itineraries at 29. Mykonos has the largest fleet with 36 vessels including replacements, yet only average performance in connections and itineraries, showing that a bigger fleet does not automatically translate into better service. Lesvos shows the highest passenger capacity per itinerary at roughly 1,600 passengers, against a low of 180 in Lefkada.
Accessibility patterns proved more consistent, with sub-indicators showing higher inter-correlation. Pserimos ranks highest in both travelled distance and estimated ticket price, indicative of limited connectivity and reliance on longer or indirect routes, while Megisti consistently ranks lowest across all accessibility measures, confirming its status as one of the most remote and isolated islands in the network. The authors note that geographic constraints remain a dominant factor shaping accessibility outcomes, limiting how far operational improvements alone can offset spatial disadvantages.
To test robustness, the team applied three weighting schemes: equal weighting, analyst-led weighting based on expert judgement, and data-driven entropy weighting. Rank correlation analysis using Spearman’s rho and Kendall’s tau showed all coefficients exceeding 0.78, indicating strong agreement in island rankings across methods. For connectivity, the strongest agreement appeared between equal and analyst-led weights, and for accessibility between equal and entropy weighting. Quadrant analysis plotting connectivity against accessibility identified a small group of islands, most notably Megisti, Karpathos and Lemnos, in the lowest-performing quadrant, below the median in both dimensions.
A systemic imbalance emerged as the dominant pattern: the majority of islands show relatively adequate accessibility but below-average connectivity, with counts varying slightly by weighting method, from 49 islands under equal weights to 56 under entropy weighting. The authors interpret this as evidence that geographic accessibility is not matched by adequate service provision in connections, itineraries and fleet deployment, suggesting policy should prioritize service frequency, direct connections and fleet deployment rather than relying solely on minimum service thresholds.
An illustrative case study of Karpathos demonstrates how the indicators work in practice. The island shows moderate connectivity and low accessibility relative to the 72 islands examined, ranking 69th out of 72 in accessibility. Its connectivity is constrained by limited direct connections and port calls, while passenger capacity per itinerary is comparatively higher, indicating that services rely on adequately sized vessels operating at low frequencies. The authors suggest that for such islands, improving service frequency and network integration through routing, scheduling or revised public service obligation specifications would likely yield more benefit than simply increasing vessel capacity, though they caution that the analysis does not incorporate demand, occupancy or operational cost data and therefore cannot conclude on optimal fleet composition.
The study acknowledges important limitations. Passenger capacity information was initially missing for 89.7 percent of the 242 vessels in the database and was filled using vessel information from public sources and mean-value imputation, while ticket prices were available for only about 4.15 percent of port pairs and were estimated using an average cost per nautical mile derived from official price schedules. These estimation procedures introduce uncertainty, and the authors stress the results should be read as indicative measures of relative performance rather than exact representations. The analyst-led weights also reflect subjective expert judgement rather than empirically validated importance, and the single baseline year of 2018 means the analysis captures no temporal dynamics.
Demand-side context helps explain the weakest performers. Megisti combines very low passenger volumes, fewer than 25,000 passenger movements in 2018, a limited tourism base of 106 hotel beds and pronounced seasonality, while Karpathos and Lemnos show August passenger movements roughly seven and ten times their February figures respectively. By contrast, Mykonos recorded more than 1.6 million passenger movements and 12,786 hotel beds. The authors argue the framework supports a transition from uniform, threshold-based policies toward differentiated, performance-oriented planning, and because it relies on generic operational characteristics, it is designed to be scalable and transferable to other island and coastal regions across Europe and beyond.
Subject of Research: Development of a composite indicator assessing short sea shipping connectivity and accessibility for territorial cohesion in Greek island regions
Article Title: A composite indicator to support short sea shipping and territorial cohesion in Greek Island regions
Article References: Perra, V.-M., & Boile, M. (2026). A composite indicator to support short sea shipping and territorial cohesion in Greek Island regions. European Transport Research Review, 18(1), Article 84. https://doi.org/10.1186/s12544-026-00837-x
Image Credits: AI Generated
DOI: 10.1186/s12544-026-00837-x
Keywords: short sea shipping, territorial cohesion, composite indicator, Greek islands, connectivity, accessibility, ferry transport, key performance indicators, transport policy, public service obligations, insularity, Aegean Sea
News Source: Denise Maddox. (October 29, 2026). New Composite Indicator Benchmarks Ferry Connectivity Across 72 Greek Islands. Scienmag.
